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+<HTML> |
+<HEAD> |
+<!-- Created by texi2html 1.56k from gperf.texi on 12 June 2003 --> |
+ |
+<TITLE>Perfect Hash Function Generator</TITLE> |
+</HEAD> |
+<BODY> |
+<H1>User's Guide to <CODE>gperf</CODE> 3.0.1</H1> |
+<H2>The GNU Perfect Hash Function Generator</H2> |
+<H2>Edition 3.0.1, 12 June 2003</H2> |
+<ADDRESS>Douglas C. Schmidt</ADDRESS> |
+<ADDRESS>Bruno Haible</ADDRESS> |
+<P> |
+<P><HR><P> |
+<H1>Table of Contents</H1> |
+<UL> |
+<LI><A NAME="TOC1" HREF="gperf.html#SEC1">GNU GENERAL PUBLIC LICENSE</A> |
+<UL> |
+<LI><A NAME="TOC2" HREF="gperf.html#SEC2">Preamble</A> |
+<LI><A NAME="TOC3" HREF="gperf.html#SEC3">How to Apply These Terms to Your New Programs</A> |
+</UL> |
+<LI><A NAME="TOC4" HREF="gperf.html#SEC4">Contributors to GNU <CODE>gperf</CODE> Utility</A> |
+<LI><A NAME="TOC5" HREF="gperf.html#SEC5">1. Introduction</A> |
+<LI><A NAME="TOC6" HREF="gperf.html#SEC6">2. Static search structures and GNU <CODE>gperf</CODE></A> |
+<LI><A NAME="TOC7" HREF="gperf.html#SEC7">3. High-Level Description of GNU <CODE>gperf</CODE></A> |
+<UL> |
+<LI><A NAME="TOC8" HREF="gperf.html#SEC8">3.1 Input Format to <CODE>gperf</CODE></A> |
+<UL> |
+<LI><A NAME="TOC9" HREF="gperf.html#SEC9">3.1.1 Declarations</A> |
+<UL> |
+<LI><A NAME="TOC10" HREF="gperf.html#SEC10">3.1.1.1 User-supplied <CODE>struct</CODE></A> |
+<LI><A NAME="TOC11" HREF="gperf.html#SEC11">3.1.1.2 Gperf Declarations</A> |
+<LI><A NAME="TOC12" HREF="gperf.html#SEC12">3.1.1.3 C Code Inclusion</A> |
+</UL> |
+<LI><A NAME="TOC13" HREF="gperf.html#SEC13">3.1.2 Format for Keyword Entries</A> |
+<LI><A NAME="TOC14" HREF="gperf.html#SEC14">3.1.3 Including Additional C Functions</A> |
+<LI><A NAME="TOC15" HREF="gperf.html#SEC15">3.1.4 Where to place directives for GNU <CODE>indent</CODE>.</A> |
+</UL> |
+<LI><A NAME="TOC16" HREF="gperf.html#SEC16">3.2 Output Format for Generated C Code with <CODE>gperf</CODE></A> |
+<LI><A NAME="TOC17" HREF="gperf.html#SEC17">3.3 Use of NUL bytes</A> |
+</UL> |
+<LI><A NAME="TOC18" HREF="gperf.html#SEC18">4. Invoking <CODE>gperf</CODE></A> |
+<UL> |
+<LI><A NAME="TOC19" HREF="gperf.html#SEC19">4.1 Specifying the Location of the Output File</A> |
+<LI><A NAME="TOC20" HREF="gperf.html#SEC20">4.2 Options that affect Interpretation of the Input File</A> |
+<LI><A NAME="TOC21" HREF="gperf.html#SEC21">4.3 Options to specify the Language for the Output Code</A> |
+<LI><A NAME="TOC22" HREF="gperf.html#SEC22">4.4 Options for fine tuning Details in the Output Code</A> |
+<LI><A NAME="TOC23" HREF="gperf.html#SEC23">4.5 Options for changing the Algorithms employed by <CODE>gperf</CODE></A> |
+<LI><A NAME="TOC24" HREF="gperf.html#SEC24">4.6 Informative Output</A> |
+</UL> |
+<LI><A NAME="TOC25" HREF="gperf.html#SEC25">5. Known Bugs and Limitations with <CODE>gperf</CODE></A> |
+<LI><A NAME="TOC26" HREF="gperf.html#SEC26">6. Things Still Left to Do</A> |
+<LI><A NAME="TOC27" HREF="gperf.html#SEC27">7. Bibliography</A> |
+<LI><A NAME="TOC28" HREF="gperf.html#SEC28">Concept Index</A> |
+</UL> |
+<P><HR><P> |
+ |
+ |
+<H1><A NAME="SEC1" HREF="gperf.html#TOC1">GNU GENERAL PUBLIC LICENSE</A></H1> |
+ |
+<P> |
+Version 2, June 1991 |
+ |
+ |
+ |
+<PRE> |
+Copyright (C) 1989, 1991 Free Software Foundation, Inc., |
+59 Temple Place, Suite 330, Boston, MA 02111-1307, USA. |
+ |
+Everyone is permitted to copy and distribute verbatim copies |
+of this license document, but changing it is not allowed. |
+</PRE> |
+ |
+ |
+ |
+<H2><A NAME="SEC2" HREF="gperf.html#TOC2">Preamble</A></H2> |
+ |
+<P> |
+ The licenses for most software are designed to take away your |
+freedom to share and change it. By contrast, the GNU General Public |
+License is intended to guarantee your freedom to share and change free |
+software--to make sure the software is free for all its users. This |
+General Public License applies to most of the Free Software |
+Foundation's software and to any other program whose authors commit to |
+using it. (Some other Free Software Foundation software is covered by |
+the GNU Library General Public License instead.) You can apply it to |
+your programs, too. |
+ |
+ |
+<P> |
+ When we speak of free software, we are referring to freedom, not |
+price. Our General Public Licenses are designed to make sure that you |
+have the freedom to distribute copies of free software (and charge for |
+this service if you wish), that you receive source code or can get it |
+if you want it, that you can change the software or use pieces of it |
+in new free programs; and that you know you can do these things. |
+ |
+ |
+<P> |
+ To protect your rights, we need to make restrictions that forbid |
+anyone to deny you these rights or to ask you to surrender the rights. |
+These restrictions translate to certain responsibilities for you if you |
+distribute copies of the software, or if you modify it. |
+ |
+ |
+<P> |
+ For example, if you distribute copies of such a program, whether |
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+ We protect your rights with two steps: (1) copyright the software, and |
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+ Finally, any free program is threatened constantly by software |
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+ The precise terms and conditions for copying, distribution and |
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+ |
+ |
+<P> |
+TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION |
+ |
+ |
+ |
+<OL> |
+<LI> |
+ |
+This License applies to any program or other work which contains |
+a notice placed by the copyright holder saying it may be distributed |
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+is covered only if its contents constitute a work based on the |
+Program (independent of having been made by running the Program). |
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+ |
+<LI> |
+ |
+You may copy and distribute verbatim copies of the Program's |
+source code as you receive it, in any medium, provided that you |
+conspicuously and appropriately publish on each copy an appropriate |
+copyright notice and disclaimer of warranty; keep intact all the |
+notices that refer to this License and to the absence of any warranty; |
+and give any other recipients of the Program a copy of this License |
+along with the Program. |
+ |
+You may charge a fee for the physical act of transferring a copy, and |
+you may at your option offer warranty protection in exchange for a fee. |
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+<LI> |
+ |
+You may modify your copy or copies of the Program or any portion |
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+<OL> |
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+ |
+You must cause the modified files to carry prominent notices |
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+You must cause any work that you distribute or publish, that in |
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+ |
+If the modified program normally reads commands interactively |
+when run, you must cause it, when started running for such |
+interactive use in the most ordinary way, to print or display an |
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+ |
+These requirements apply to the modified work as a whole. If |
+identifiable sections of that work are not derived from the Program, |
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+Thus, it is not the intent of this section to claim rights or contest |
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+ |
+In addition, mere aggregation of another work not based on the Program |
+with the Program (or with a work based on the Program) on a volume of |
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+ |
+<LI> |
+ |
+You may copy and distribute the Program (or a work based on it, |
+under Section 2) in object code or executable form under the terms of |
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+ |
+ |
+<OL> |
+<LI> |
+ |
+Accompany it with the complete corresponding machine-readable |
+source code, which must be distributed under the terms of Sections |
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+ |
+<LI> |
+ |
+Accompany it with a written offer, valid for at least three |
+years, to give any third party, for a charge no more than your |
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+customarily used for software interchange; or, |
+ |
+<LI> |
+ |
+Accompany it with the information you received as to the offer |
+to distribute corresponding source code. (This alternative is |
+allowed only for noncommercial distribution and only if you |
+received the program in object code or executable form with such |
+an offer, in accord with Subsection b above.) |
+</OL> |
+ |
+The source code for a work means the preferred form of the work for |
+making modifications to it. For an executable work, complete source |
+code means all the source code for all modules it contains, plus any |
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+operating system on which the executable runs, unless that component |
+itself accompanies the executable. |
+ |
+If distribution of executable or object code is made by offering |
+access to copy from a designated place, then offering equivalent |
+access to copy the source code from the same place counts as |
+distribution of the source code, even though third parties are not |
+compelled to copy the source along with the object code. |
+ |
+<LI> |
+ |
+You may not copy, modify, sublicense, or distribute the Program |
+except as expressly provided under this License. Any attempt |
+otherwise to copy, modify, sublicense or distribute the Program is |
+void, and will automatically terminate your rights under this License. |
+However, parties who have received copies, or rights, from you under |
+this License will not have their licenses terminated so long as such |
+parties remain in full compliance. |
+ |
+<LI> |
+ |
+You are not required to accept this License, since you have not |
+signed it. However, nothing else grants you permission to modify or |
+distribute the Program or its derivative works. These actions are |
+prohibited by law if you do not accept this License. Therefore, by |
+modifying or distributing the Program (or any work based on the |
+Program), you indicate your acceptance of this License to do so, and |
+all its terms and conditions for copying, distributing or modifying |
+the Program or works based on it. |
+ |
+<LI> |
+ |
+Each time you redistribute the Program (or any work based on the |
+Program), the recipient automatically receives a license from the |
+original licensor to copy, distribute or modify the Program subject to |
+these terms and conditions. You may not impose any further |
+restrictions on the recipients' exercise of the rights granted herein. |
+You are not responsible for enforcing compliance by third parties to |
+this License. |
+ |
+<LI> |
+ |
+If, as a consequence of a court judgment or allegation of patent |
+infringement or for any other reason (not limited to patent issues), |
+conditions are imposed on you (whether by court order, agreement or |
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+refrain entirely from distribution of the Program. |
+ |
+If any portion of this section is held invalid or unenforceable under |
+any particular circumstance, the balance of the section is intended to |
+apply and the section as a whole is intended to apply in other |
+circumstances. |
+ |
+It is not the purpose of this section to induce you to infringe any |
+patents or other property right claims or to contest validity of any |
+such claims; this section has the sole purpose of protecting the |
+integrity of the free software distribution system, which is |
+implemented by public license practices. Many people have made |
+generous contributions to the wide range of software distributed |
+through that system in reliance on consistent application of that |
+system; it is up to the author/donor to decide if he or she is willing |
+to distribute software through any other system and a licensee cannot |
+impose that choice. |
+ |
+This section is intended to make thoroughly clear what is believed to |
+be a consequence of the rest of this License. |
+ |
+<LI> |
+ |
+If the distribution and/or use of the Program is restricted in |
+certain countries either by patents or by copyrighted interfaces, the |
+original copyright holder who places the Program under this License |
+may add an explicit geographical distribution limitation excluding |
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+countries not thus excluded. In such case, this License incorporates |
+the limitation as if written in the body of this License. |
+ |
+<LI> |
+ |
+The Free Software Foundation may publish revised and/or new versions |
+of the General Public License from time to time. Such new versions will |
+be similar in spirit to the present version, but may differ in detail to |
+address new problems or concerns. |
+ |
+Each version is given a distinguishing version number. If the Program |
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+later version", you have the option of following the terms and conditions |
+either of that version or of any later version published by the Free |
+Software Foundation. If the Program does not specify a version number of |
+this License, you may choose any version ever published by the Free Software |
+Foundation. |
+ |
+<LI> |
+ |
+If you wish to incorporate parts of the Program into other free |
+programs whose distribution conditions are different, write to the author |
+to ask for permission. For software which is copyrighted by the Free |
+Software Foundation, write to the Free Software Foundation; we sometimes |
+make exceptions for this. Our decision will be guided by the two goals |
+of preserving the free status of all derivatives of our free software and |
+of promoting the sharing and reuse of software generally. |
+ |
+NO WARRANTY |
+ |
+<LI> |
+ |
+BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY |
+FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN |
+OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES |
+PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED |
+OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF |
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS |
+TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE |
+PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, |
+REPAIR OR CORRECTION. |
+ |
+<LI> |
+ |
+IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING |
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR |
+REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, |
+INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING |
+OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED |
+TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY |
+YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER |
+PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE |
+POSSIBILITY OF SUCH DAMAGES. |
+</OL> |
+ |
+<P> |
+END OF TERMS AND CONDITIONS |
+ |
+ |
+ |
+ |
+<H2><A NAME="SEC3" HREF="gperf.html#TOC3">How to Apply These Terms to Your New Programs</A></H2> |
+ |
+<P> |
+ If you develop a new program, and you want it to be of the greatest |
+possible use to the public, the best way to achieve this is to make it |
+free software which everyone can redistribute and change under these terms. |
+ |
+ |
+<P> |
+ To do so, attach the following notices to the program. It is safest |
+to attach them to the start of each source file to most effectively |
+convey the exclusion of warranty; and each file should have at least |
+the "copyright" line and a pointer to where the full notice is found. |
+ |
+ |
+ |
+<PRE> |
+<VAR>one line to give the program's name and an idea of what it does.</VAR> |
+Copyright (C) <VAR>year</VAR> <VAR>name of author</VAR> |
+ |
+This program is free software; you can redistribute it and/or |
+modify it under the terms of the GNU General Public License |
+as published by the Free Software Foundation; either version 2 |
+of the License, or (at your option) any later version. |
+ |
+This program is distributed in the hope that it will be useful, |
+but WITHOUT ANY WARRANTY; without even the implied warranty of |
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
+GNU General Public License for more details. |
+ |
+You should have received a copy of the GNU General Public License |
+along with this program; if not, write to the Free Software |
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA. |
+</PRE> |
+ |
+<P> |
+Also add information on how to contact you by electronic and paper mail. |
+ |
+ |
+<P> |
+If the program is interactive, make it output a short notice like this |
+when it starts in an interactive mode: |
+ |
+ |
+ |
+<PRE> |
+Gnomovision version 69, Copyright (C) <VAR>year</VAR> <VAR>name of author</VAR> |
+Gnomovision comes with ABSOLUTELY NO WARRANTY; for details |
+type `show w'. This is free software, and you are welcome |
+to redistribute it under certain conditions; type `show c' |
+for details. |
+</PRE> |
+ |
+<P> |
+The hypothetical commands <SAMP>`show w'</SAMP> and <SAMP>`show c'</SAMP> should show |
+the appropriate parts of the General Public License. Of course, the |
+commands you use may be called something other than <SAMP>`show w'</SAMP> and |
+<SAMP>`show c'</SAMP>; they could even be mouse-clicks or menu items--whatever |
+suits your program. |
+ |
+ |
+<P> |
+You should also get your employer (if you work as a programmer) or your |
+school, if any, to sign a "copyright disclaimer" for the program, if |
+necessary. Here is a sample; alter the names: |
+ |
+ |
+ |
+<PRE> |
+Yoyodyne, Inc., hereby disclaims all copyright |
+interest in the program `Gnomovision' |
+(which makes passes at compilers) written |
+by James Hacker. |
+ |
+<VAR>signature of Ty Coon</VAR>, 1 April 1989 |
+Ty Coon, President of Vice |
+</PRE> |
+ |
+<P> |
+This General Public License does not permit incorporating your program into |
+proprietary programs. If your program is a subroutine library, you may |
+consider it more useful to permit linking proprietary applications with the |
+library. If this is what you want to do, use the GNU Library General |
+Public License instead of this License. |
+ |
+ |
+ |
+ |
+<H1><A NAME="SEC4" HREF="gperf.html#TOC4">Contributors to GNU <CODE>gperf</CODE> Utility</A></H1> |
+ |
+ |
+<UL> |
+<LI> |
+ |
+<A NAME="IDX1"></A> |
+The GNU <CODE>gperf</CODE> perfect hash function generator utility was |
+written in GNU C++ by Douglas C. Schmidt. The general |
+idea for the perfect hash function generator was inspired by Keith |
+Bostic's algorithm written in C, and distributed to net.sources around |
+1984. The current program is a heavily modified, enhanced, and extended |
+implementation of Keith's basic idea, created at the University of |
+California, Irvine. Bugs, patches, and suggestions should be reported |
+to <CODE><bug-gnu-gperf@gnu.org></CODE>. |
+ |
+<LI> |
+ |
+Special thanks is extended to Michael Tiemann and Doug Lea, for |
+providing a useful compiler, and for giving me a forum to exhibit my |
+creation. |
+ |
+In addition, Adam de Boor and Nels Olson provided many tips and insights |
+that greatly helped improve the quality and functionality of <CODE>gperf</CODE>. |
+ |
+<LI> |
+ |
+Bruno Haible enhanced and optimized the search algorithm. He also rewrote |
+the input routines and the output routines for better reliability, and |
+added a testsuite. |
+</UL> |
+ |
+ |
+ |
+<H1><A NAME="SEC5" HREF="gperf.html#TOC5">1. Introduction</A></H1> |
+ |
+<P> |
+<CODE>gperf</CODE> is a perfect hash function generator written in C++. It |
+transforms an <VAR>n</VAR> element user-specified keyword set <VAR>W</VAR> into a |
+perfect hash function <VAR>F</VAR>. <VAR>F</VAR> uniquely maps keywords in |
+<VAR>W</VAR> onto the range 0..<VAR>k</VAR>, where <VAR>k</VAR> >= <VAR>n-1</VAR>. If <VAR>k</VAR> |
+= <VAR>n-1</VAR> then <VAR>F</VAR> is a <EM>minimal</EM> perfect hash function. |
+<CODE>gperf</CODE> generates a 0..<VAR>k</VAR> element static lookup table and a |
+pair of C functions. These functions determine whether a given |
+character string <VAR>s</VAR> occurs in <VAR>W</VAR>, using at most one probe into |
+the lookup table. |
+ |
+ |
+<P> |
+<CODE>gperf</CODE> currently generates the reserved keyword recognizer for |
+lexical analyzers in several production and research compilers and |
+language processing tools, including GNU C, GNU C++, GNU Java, GNU Pascal, |
+GNU Modula 3, and GNU indent. Complete C++ source code for <CODE>gperf</CODE> is |
+available from <CODE>http://ftp.gnu.org/pub/gnu/gperf/</CODE>. |
+A paper describing <CODE>gperf</CODE>'s design and implementation in greater |
+detail is available in the Second USENIX C++ Conference proceedings |
+or from <CODE>http://www.cs.wustl.edu/~schmidt/resume.html</CODE>. |
+ |
+ |
+ |
+ |
+<H1><A NAME="SEC6" HREF="gperf.html#TOC6">2. Static search structures and GNU <CODE>gperf</CODE></A></H1> |
+<P> |
+<A NAME="IDX2"></A> |
+ |
+ |
+<P> |
+A <EM>static search structure</EM> is an Abstract Data Type with certain |
+fundamental operations, e.g., <EM>initialize</EM>, <EM>insert</EM>, |
+and <EM>retrieve</EM>. Conceptually, all insertions occur before any |
+retrievals. In practice, <CODE>gperf</CODE> generates a <EM>static</EM> array |
+containing search set keywords and any associated attributes specified |
+by the user. Thus, there is essentially no execution-time cost for the |
+insertions. It is a useful data structure for representing <EM>static |
+search sets</EM>. Static search sets occur frequently in software system |
+applications. Typical static search sets include compiler reserved |
+words, assembler instruction opcodes, and built-in shell interpreter |
+commands. Search set members, called <EM>keywords</EM>, are inserted into |
+the structure only once, usually during program initialization, and are |
+not generally modified at run-time. |
+ |
+ |
+<P> |
+Numerous static search structure implementations exist, e.g., |
+arrays, linked lists, binary search trees, digital search tries, and |
+hash tables. Different approaches offer trade-offs between space |
+utilization and search time efficiency. For example, an <VAR>n</VAR> element |
+sorted array is space efficient, though the average-case time |
+complexity for retrieval operations using binary search is |
+proportional to log <VAR>n</VAR>. Conversely, hash table implementations |
+often locate a table entry in constant time, but typically impose |
+additional memory overhead and exhibit poor worst case performance. |
+ |
+ |
+<P> |
+<A NAME="IDX3"></A> |
+<EM>Minimal perfect hash functions</EM> provide an optimal solution for a |
+particular class of static search sets. A minimal perfect hash |
+function is defined by two properties: |
+ |
+ |
+ |
+<UL> |
+<LI> |
+ |
+It allows keyword recognition in a static search set using at most |
+<EM>one</EM> probe into the hash table. This represents the "perfect" |
+property. |
+<LI> |
+ |
+The actual memory allocated to store the keywords is precisely large |
+enough for the keyword set, and <EM>no larger</EM>. This is the |
+"minimal" property. |
+</UL> |
+ |
+<P> |
+For most applications it is far easier to generate <EM>perfect</EM> hash |
+functions than <EM>minimal perfect</EM> hash functions. Moreover, |
+non-minimal perfect hash functions frequently execute faster than |
+minimal ones in practice. This phenomena occurs since searching a |
+sparse keyword table increases the probability of locating a "null" |
+entry, thereby reducing string comparisons. <CODE>gperf</CODE>'s default |
+behavior generates <EM>near-minimal</EM> perfect hash functions for |
+keyword sets. However, <CODE>gperf</CODE> provides many options that permit |
+user control over the degree of minimality and perfection. |
+ |
+ |
+<P> |
+Static search sets often exhibit relative stability over time. For |
+example, Ada's 63 reserved words have remained constant for nearly a |
+decade. It is therefore frequently worthwhile to expend concerted |
+effort building an optimal search structure <EM>once</EM>, if it |
+subsequently receives heavy use multiple times. <CODE>gperf</CODE> removes |
+the drudgery associated with constructing time- and space-efficient |
+search structures by hand. It has proven a useful and practical tool |
+for serious programming projects. Output from <CODE>gperf</CODE> is currently |
+used in several production and research compilers, including GNU C, GNU |
+C++, GNU Java, GNU Pascal, and GNU Modula 3. The latter two compilers are |
+not yet part of the official GNU distribution. Each compiler utilizes |
+<CODE>gperf</CODE> to automatically generate static search structures that |
+efficiently identify their respective reserved keywords. |
+ |
+ |
+ |
+ |
+<H1><A NAME="SEC7" HREF="gperf.html#TOC7">3. High-Level Description of GNU <CODE>gperf</CODE></A></H1> |
+ |
+<P> |
+The perfect hash function generator <CODE>gperf</CODE> reads a set of |
+"keywords" from an input file (or from the standard input by |
+default). It attempts to derive a perfect hashing function that |
+recognizes a member of the <EM>static keyword set</EM> with at most a |
+single probe into the lookup table. If <CODE>gperf</CODE> succeeds in |
+generating such a function it produces a pair of C source code routines |
+that perform hashing and table lookup recognition. All generated C code |
+is directed to the standard output. Command-line options described |
+below allow you to modify the input and output format to <CODE>gperf</CODE>. |
+ |
+ |
+<P> |
+By default, <CODE>gperf</CODE> attempts to produce time-efficient code, with |
+less emphasis on efficient space utilization. However, several options |
+exist that permit trading-off execution time for storage space and vice |
+versa. In particular, expanding the generated table size produces a |
+sparse search structure, generally yielding faster searches. |
+Conversely, you can direct <CODE>gperf</CODE> to utilize a C <CODE>switch</CODE> |
+statement scheme that minimizes data space storage size. Furthermore, |
+using a C <CODE>switch</CODE> may actually speed up the keyword retrieval time |
+somewhat. Actual results depend on your C compiler, of course. |
+ |
+ |
+<P> |
+In general, <CODE>gperf</CODE> assigns values to the bytes it is using |
+for hashing until some set of values gives each keyword a unique value. |
+A helpful heuristic is that the larger the hash value range, the easier |
+it is for <CODE>gperf</CODE> to find and generate a perfect hash function. |
+Experimentation is the key to getting the most from <CODE>gperf</CODE>. |
+ |
+ |
+ |
+ |
+<H2><A NAME="SEC8" HREF="gperf.html#TOC8">3.1 Input Format to <CODE>gperf</CODE></A></H2> |
+<P> |
+<A NAME="IDX4"></A> |
+<A NAME="IDX5"></A> |
+<A NAME="IDX6"></A> |
+<A NAME="IDX7"></A> |
+You can control the input file format by varying certain command-line |
+arguments, in particular the <SAMP>`-t'</SAMP> option. The input's appearance |
+is similar to GNU utilities <CODE>flex</CODE> and <CODE>bison</CODE> (or UNIX |
+utilities <CODE>lex</CODE> and <CODE>yacc</CODE>). Here's an outline of the general |
+format: |
+ |
+ |
+ |
+<PRE> |
+declarations |
+%% |
+keywords |
+%% |
+functions |
+</PRE> |
+ |
+<P> |
+<EM>Unlike</EM> <CODE>flex</CODE> or <CODE>bison</CODE>, the declarations section and |
+the functions section are optional. The following sections describe the |
+input format for each section. |
+ |
+ |
+<P> |
+It is possible to omit the declaration section entirely, if the <SAMP>`-t'</SAMP> |
+option is not given. In this case the input file begins directly with the |
+first keyword line, e.g.: |
+ |
+ |
+ |
+<PRE> |
+january |
+february |
+march |
+april |
+... |
+</PRE> |
+ |
+ |
+ |
+<H3><A NAME="SEC9" HREF="gperf.html#TOC9">3.1.1 Declarations</A></H3> |
+ |
+<P> |
+The keyword input file optionally contains a section for including |
+arbitrary C declarations and definitions, <CODE>gperf</CODE> declarations that |
+act like command-line options, as well as for providing a user-supplied |
+<CODE>struct</CODE>. |
+ |
+ |
+ |
+ |
+<H4><A NAME="SEC10" HREF="gperf.html#TOC10">3.1.1.1 User-supplied <CODE>struct</CODE></A></H4> |
+ |
+<P> |
+If the <SAMP>`-t'</SAMP> option (or, equivalently, the <SAMP>`%struct-type'</SAMP> declaration) |
+<EM>is</EM> enabled, you <EM>must</EM> provide a C <CODE>struct</CODE> as the last |
+component in the declaration section from the input file. The first |
+field in this struct must be of type <CODE>char *</CODE> or <CODE>const char *</CODE> |
+if the <SAMP>`-P'</SAMP> option is not given, or of type <CODE>int</CODE> if the option |
+<SAMP>`-P'</SAMP> (or, equivalently, the <SAMP>`%pic'</SAMP> declaration) is enabled. |
+This first field must be called <SAMP>`name'</SAMP>, although it is possible to modify |
+its name with the <SAMP>`-K'</SAMP> option (or, equivalently, the |
+<SAMP>`%define slot-name'</SAMP> declaration) described below. |
+ |
+ |
+<P> |
+Here is a simple example, using months of the year and their attributes as |
+input: |
+ |
+ |
+ |
+<PRE> |
+struct month { char *name; int number; int days; int leap_days; }; |
+%% |
+january, 1, 31, 31 |
+february, 2, 28, 29 |
+march, 3, 31, 31 |
+april, 4, 30, 30 |
+may, 5, 31, 31 |
+june, 6, 30, 30 |
+july, 7, 31, 31 |
+august, 8, 31, 31 |
+september, 9, 30, 30 |
+october, 10, 31, 31 |
+november, 11, 30, 30 |
+december, 12, 31, 31 |
+</PRE> |
+ |
+<P> |
+<A NAME="IDX8"></A> |
+Separating the <CODE>struct</CODE> declaration from the list of keywords and |
+other fields are a pair of consecutive percent signs, <SAMP>`%%'</SAMP>, |
+appearing left justified in the first column, as in the UNIX utility |
+<CODE>lex</CODE>. |
+ |
+ |
+<P> |
+If the <CODE>struct</CODE> has already been declared in an include file, it can |
+be mentioned in an abbreviated form, like this: |
+ |
+ |
+ |
+<PRE> |
+struct month; |
+%% |
+january, 1, 31, 31 |
+... |
+</PRE> |
+ |
+ |
+ |
+<H4><A NAME="SEC11" HREF="gperf.html#TOC11">3.1.1.2 Gperf Declarations</A></H4> |
+ |
+<P> |
+The declaration section can contain <CODE>gperf</CODE> declarations. They |
+influence the way <CODE>gperf</CODE> works, like command line options do. |
+In fact, every such declaration is equivalent to a command line option. |
+There are three forms of declarations: |
+ |
+ |
+ |
+<OL> |
+<LI> |
+ |
+Declarations without argument, like <SAMP>`%compare-lengths'</SAMP>. |
+ |
+<LI> |
+ |
+Declarations with an argument, like <SAMP>`%switch=<VAR>count</VAR>'</SAMP>. |
+ |
+<LI> |
+ |
+Declarations of names of entities in the output file, like |
+<SAMP>`%define lookup-function-name <VAR>name</VAR>'</SAMP>. |
+</OL> |
+ |
+<P> |
+When a declaration is given both in the input file and as a command line |
+option, the command-line option's value prevails. |
+ |
+ |
+<P> |
+The following <CODE>gperf</CODE> declarations are available. |
+ |
+ |
+<DL COMPACT> |
+ |
+<DT><SAMP>`%delimiters=<VAR>delimiter-list</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX9"></A> |
+Allows you to provide a string containing delimiters used to |
+separate keywords from their attributes. The default is ",". This |
+option is essential if you want to use keywords that have embedded |
+commas or newlines. |
+ |
+<DT><SAMP>`%struct-type'</SAMP> |
+<DD> |
+<A NAME="IDX10"></A> |
+Allows you to include a <CODE>struct</CODE> type declaration for generated |
+code; see above for an example. |
+ |
+<DT><SAMP>`%ignore-case'</SAMP> |
+<DD> |
+<A NAME="IDX11"></A> |
+Consider upper and lower case ASCII characters as equivalent. The string |
+comparison will use a case insignificant character comparison. Note that |
+locale dependent case mappings are ignored. |
+ |
+<DT><SAMP>`%language=<VAR>language-name</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX12"></A> |
+Instructs <CODE>gperf</CODE> to generate code in the language specified by the |
+option's argument. Languages handled are currently: |
+ |
+<DL COMPACT> |
+ |
+<DT><SAMP>`KR-C'</SAMP> |
+<DD> |
+Old-style K&R C. This language is understood by old-style C compilers and |
+ANSI C compilers, but ANSI C compilers may flag warnings (or even errors) |
+because of lacking <SAMP>`const'</SAMP>. |
+ |
+<DT><SAMP>`C'</SAMP> |
+<DD> |
+Common C. This language is understood by ANSI C compilers, and also by |
+old-style C compilers, provided that you <CODE>#define const</CODE> to empty |
+for compilers which don't know about this keyword. |
+ |
+<DT><SAMP>`ANSI-C'</SAMP> |
+<DD> |
+ANSI C. This language is understood by ANSI C compilers and C++ compilers. |
+ |
+<DT><SAMP>`C++'</SAMP> |
+<DD> |
+C++. This language is understood by C++ compilers. |
+</DL> |
+ |
+The default is C. |
+ |
+<DT><SAMP>`%define slot-name <VAR>name</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX13"></A> |
+This declaration is only useful when option <SAMP>`-t'</SAMP> (or, equivalently, the |
+<SAMP>`%struct-type'</SAMP> declaration) has been given. |
+By default, the program assumes the structure component identifier for |
+the keyword is <SAMP>`name'</SAMP>. This option allows an arbitrary choice of |
+identifier for this component, although it still must occur as the first |
+field in your supplied <CODE>struct</CODE>. |
+ |
+<DT><SAMP>`%define initializer-suffix <VAR>initializers</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX14"></A> |
+This declaration is only useful when option <SAMP>`-t'</SAMP> (or, equivalently, the |
+<SAMP>`%struct-type'</SAMP> declaration) has been given. |
+It permits to specify initializers for the structure members following |
+<VAR>slot-name</VAR> in empty hash table entries. The list of initializers |
+should start with a comma. By default, the emitted code will |
+zero-initialize structure members following <VAR>slot-name</VAR>. |
+ |
+<DT><SAMP>`%define hash-function-name <VAR>name</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX15"></A> |
+Allows you to specify the name for the generated hash function. Default |
+name is <SAMP>`hash'</SAMP>. This option permits the use of two hash tables in |
+the same file. |
+ |
+<DT><SAMP>`%define lookup-function-name <VAR>name</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX16"></A> |
+Allows you to specify the name for the generated lookup function. |
+Default name is <SAMP>`in_word_set'</SAMP>. This option permits multiple |
+generated hash functions to be used in the same application. |
+ |
+<DT><SAMP>`%define class-name <VAR>name</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX17"></A> |
+This option is only useful when option <SAMP>`-L C++'</SAMP> (or, equivalently, |
+the <SAMP>`%language=C++'</SAMP> declaration) has been given. It |
+allows you to specify the name of generated C++ class. Default name is |
+<CODE>Perfect_Hash</CODE>. |
+ |
+<DT><SAMP>`%7bit'</SAMP> |
+<DD> |
+<A NAME="IDX18"></A> |
+This option specifies that all strings that will be passed as arguments |
+to the generated hash function and the generated lookup function will |
+solely consist of 7-bit ASCII characters (bytes in the range 0..127). |
+(Note that the ANSI C functions <CODE>isalnum</CODE> and <CODE>isgraph</CODE> do |
+<EM>not</EM> guarantee that a byte is in this range. Only an explicit |
+test like <SAMP>`c >= 'A' && c <= 'Z''</SAMP> guarantees this.) |
+ |
+<DT><SAMP>`%compare-lengths'</SAMP> |
+<DD> |
+<A NAME="IDX19"></A> |
+Compare keyword lengths before trying a string comparison. This option |
+is mandatory for binary comparisons (see section <A HREF="gperf.html#SEC17">3.3 Use of NUL bytes</A>). It also might |
+cut down on the number of string comparisons made during the lookup, since |
+keywords with different lengths are never compared via <CODE>strcmp</CODE>. |
+However, using <SAMP>`%compare-lengths'</SAMP> might greatly increase the size of the |
+generated C code if the lookup table range is large (which implies that |
+the switch option <SAMP>`-S'</SAMP> or <SAMP>`%switch'</SAMP> is not enabled), since the length |
+table contains as many elements as there are entries in the lookup table. |
+ |
+<DT><SAMP>`%compare-strncmp'</SAMP> |
+<DD> |
+<A NAME="IDX20"></A> |
+Generates C code that uses the <CODE>strncmp</CODE> function to perform |
+string comparisons. The default action is to use <CODE>strcmp</CODE>. |
+ |
+<DT><SAMP>`%readonly-tables'</SAMP> |
+<DD> |
+<A NAME="IDX21"></A> |
+Makes the contents of all generated lookup tables constant, i.e., |
+"readonly". Many compilers can generate more efficient code for this |
+by putting the tables in readonly memory. |
+ |
+<DT><SAMP>`%enum'</SAMP> |
+<DD> |
+<A NAME="IDX22"></A> |
+Define constant values using an enum local to the lookup function rather |
+than with #defines. This also means that different lookup functions can |
+reside in the same file. Thanks to James Clark <CODE><jjc@ai.mit.edu></CODE>. |
+ |
+<DT><SAMP>`%includes'</SAMP> |
+<DD> |
+<A NAME="IDX23"></A> |
+Include the necessary system include file, <CODE><string.h></CODE>, at the |
+beginning of the code. By default, this is not done; the user must |
+include this header file himself to allow compilation of the code. |
+ |
+<DT><SAMP>`%global-table'</SAMP> |
+<DD> |
+<A NAME="IDX24"></A> |
+Generate the static table of keywords as a static global variable, |
+rather than hiding it inside of the lookup function (which is the |
+default behavior). |
+ |
+<DT><SAMP>`%pic'</SAMP> |
+<DD> |
+<A NAME="IDX25"></A> |
+Optimize the generated table for inclusion in shared libraries. This |
+reduces the startup time of programs using a shared library containing |
+the generated code. If the <SAMP>`%struct-type'</SAMP> declaration (or, |
+equivalently, the option <SAMP>`-t'</SAMP>) is also given, the first field of the |
+user-defined struct must be of type <SAMP>`int'</SAMP>, not <SAMP>`char *'</SAMP>, because |
+it will contain offsets into the string pool instead of actual strings. |
+To convert such an offset to a string, you can use the expression |
+<SAMP>`stringpool + <VAR>o</VAR>'</SAMP>, where <VAR>o</VAR> is the offset. The string pool |
+name can be changed through the <SAMP>`%define string-pool-name'</SAMP> declaration. |
+ |
+<DT><SAMP>`%define string-pool-name <VAR>name</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX26"></A> |
+Allows you to specify the name of the generated string pool created by |
+the declaration <SAMP>`%pic'</SAMP> (or, equivalently, the option <SAMP>`-P'</SAMP>). |
+The default name is <SAMP>`stringpool'</SAMP>. This declaration permits the use of |
+two hash tables in the same file, with <SAMP>`%pic'</SAMP> and even when the |
+<SAMP>`%global-table'</SAMP> declaration (or, equivalently, the option <SAMP>`-G'</SAMP>) |
+is given. |
+ |
+<DT><SAMP>`%null-strings'</SAMP> |
+<DD> |
+<A NAME="IDX27"></A> |
+Use NULL strings instead of empty strings for empty keyword table entries. |
+This reduces the startup time of programs using a shared library containing |
+the generated code (but not as much as the declaration <SAMP>`%pic'</SAMP>), at the |
+expense of one more test-and-branch instruction at run time. |
+ |
+<DT><SAMP>`%define word-array-name <VAR>name</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX28"></A> |
+Allows you to specify the name for the generated array containing the |
+hash table. Default name is <SAMP>`wordlist'</SAMP>. This option permits the |
+use of two hash tables in the same file, even when the option <SAMP>`-G'</SAMP> |
+(or, equivalently, the <SAMP>`%global-table'</SAMP> declaration) is given. |
+ |
+<DT><SAMP>`%switch=<VAR>count</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX29"></A> |
+Causes the generated C code to use a <CODE>switch</CODE> statement scheme, |
+rather than an array lookup table. This can lead to a reduction in both |
+time and space requirements for some input files. The argument to this |
+option determines how many <CODE>switch</CODE> statements are generated. A |
+value of 1 generates 1 <CODE>switch</CODE> containing all the elements, a |
+value of 2 generates 2 tables with 1/2 the elements in each |
+<CODE>switch</CODE>, etc. This is useful since many C compilers cannot |
+correctly generate code for large <CODE>switch</CODE> statements. This option |
+was inspired in part by Keith Bostic's original C program. |
+ |
+<DT><SAMP>`%omit-struct-type'</SAMP> |
+<DD> |
+<A NAME="IDX30"></A> |
+Prevents the transfer of the type declaration to the output file. Use |
+this option if the type is already defined elsewhere. |
+</DL> |
+ |
+ |
+ |
+<H4><A NAME="SEC12" HREF="gperf.html#TOC12">3.1.1.3 C Code Inclusion</A></H4> |
+ |
+<P> |
+<A NAME="IDX31"></A> |
+<A NAME="IDX32"></A> |
+Using a syntax similar to GNU utilities <CODE>flex</CODE> and <CODE>bison</CODE>, it |
+is possible to directly include C source text and comments verbatim into |
+the generated output file. This is accomplished by enclosing the region |
+inside left-justified surrounding <SAMP>`%{'</SAMP>, <SAMP>`%}'</SAMP> pairs. Here is |
+an input fragment based on the previous example that illustrates this |
+feature: |
+ |
+ |
+ |
+<PRE> |
+%{ |
+#include <assert.h> |
+/* This section of code is inserted directly into the output. */ |
+int return_month_days (struct month *months, int is_leap_year); |
+%} |
+struct month { char *name; int number; int days; int leap_days; }; |
+%% |
+january, 1, 31, 31 |
+february, 2, 28, 29 |
+march, 3, 31, 31 |
+... |
+</PRE> |
+ |
+ |
+ |
+<H3><A NAME="SEC13" HREF="gperf.html#TOC13">3.1.2 Format for Keyword Entries</A></H3> |
+ |
+<P> |
+The second input file format section contains lines of keywords and any |
+associated attributes you might supply. A line beginning with <SAMP>`#'</SAMP> |
+in the first column is considered a comment. Everything following the |
+<SAMP>`#'</SAMP> is ignored, up to and including the following newline. A line |
+beginning with <SAMP>`%'</SAMP> in the first column is an option declaration and |
+must not occur within the keywords section. |
+ |
+ |
+<P> |
+The first field of each non-comment line is always the keyword itself. It |
+can be given in two ways: as a simple name, i.e., without surrounding |
+string quotation marks, or as a string enclosed in double-quotes, in |
+C syntax, possibly with backslash escapes like <CODE>\"</CODE> or <CODE>\234</CODE> |
+or <CODE>\xa8</CODE>. In either case, it must start right at the beginning |
+of the line, without leading whitespace. |
+In this context, a "field" is considered to extend up to, but |
+not include, the first blank, comma, or newline. Here is a simple |
+example taken from a partial list of C reserved words: |
+ |
+ |
+ |
+<PRE> |
+# These are a few C reserved words, see the c.gperf file |
+# for a complete list of ANSI C reserved words. |
+unsigned |
+sizeof |
+switch |
+signed |
+if |
+default |
+for |
+while |
+return |
+</PRE> |
+ |
+<P> |
+Note that unlike <CODE>flex</CODE> or <CODE>bison</CODE> the first <SAMP>`%%'</SAMP> marker |
+may be elided if the declaration section is empty. |
+ |
+ |
+<P> |
+Additional fields may optionally follow the leading keyword. Fields |
+should be separated by commas, and terminate at the end of line. What |
+these fields mean is entirely up to you; they are used to initialize the |
+elements of the user-defined <CODE>struct</CODE> provided by you in the |
+declaration section. If the <SAMP>`-t'</SAMP> option (or, equivalently, the |
+<SAMP>`%struct-type'</SAMP> declaration) is <EM>not</EM> enabled |
+these fields are simply ignored. All previous examples except the last |
+one contain keyword attributes. |
+ |
+ |
+ |
+ |
+<H3><A NAME="SEC14" HREF="gperf.html#TOC14">3.1.3 Including Additional C Functions</A></H3> |
+ |
+<P> |
+The optional third section also corresponds closely with conventions |
+found in <CODE>flex</CODE> and <CODE>bison</CODE>. All text in this section, |
+starting at the final <SAMP>`%%'</SAMP> and extending to the end of the input |
+file, is included verbatim into the generated output file. Naturally, |
+it is your responsibility to ensure that the code contained in this |
+section is valid C. |
+ |
+ |
+ |
+ |
+<H3><A NAME="SEC15" HREF="gperf.html#TOC15">3.1.4 Where to place directives for GNU <CODE>indent</CODE>.</A></H3> |
+ |
+<P> |
+If you want to invoke GNU <CODE>indent</CODE> on a <CODE>gperf</CODE> input file, |
+you will see that GNU <CODE>indent</CODE> doesn't understand the <SAMP>`%%'</SAMP>, |
+<SAMP>`%{'</SAMP> and <SAMP>`%}'</SAMP> directives that control <CODE>gperf</CODE>'s |
+interpretation of the input file. Therefore you have to insert some |
+directives for GNU <CODE>indent</CODE>. More precisely, assuming the most |
+general input file structure |
+ |
+ |
+ |
+<PRE> |
+declarations part 1 |
+%{ |
+verbatim code |
+%} |
+declarations part 2 |
+%% |
+keywords |
+%% |
+functions |
+</PRE> |
+ |
+<P> |
+you would insert <SAMP>`*INDENT-OFF*'</SAMP> and <SAMP>`*INDENT-ON*'</SAMP> comments |
+as follows: |
+ |
+ |
+ |
+<PRE> |
+/* *INDENT-OFF* */ |
+declarations part 1 |
+%{ |
+/* *INDENT-ON* */ |
+verbatim code |
+/* *INDENT-OFF* */ |
+%} |
+declarations part 2 |
+%% |
+keywords |
+%% |
+/* *INDENT-ON* */ |
+functions |
+</PRE> |
+ |
+ |
+ |
+<H2><A NAME="SEC16" HREF="gperf.html#TOC16">3.2 Output Format for Generated C Code with <CODE>gperf</CODE></A></H2> |
+<P> |
+<A NAME="IDX33"></A> |
+ |
+ |
+<P> |
+Several options control how the generated C code appears on the standard |
+output. Two C function are generated. They are called <CODE>hash</CODE> and |
+<CODE>in_word_set</CODE>, although you may modify their names with a command-line |
+option. Both functions require two arguments, a string, <CODE>char *</CODE> |
+<VAR>str</VAR>, and a length parameter, <CODE>int</CODE> <VAR>len</VAR>. Their default |
+function prototypes are as follows: |
+ |
+ |
+<P> |
+<DL> |
+<DT><U>Function:</U> unsigned int <B>hash</B> <I>(const char * <VAR>str</VAR>, unsigned int <VAR>len</VAR>)</I> |
+<DD><A NAME="IDX34"></A> |
+By default, the generated <CODE>hash</CODE> function returns an integer value |
+created by adding <VAR>len</VAR> to several user-specified <VAR>str</VAR> byte |
+positions indexed into an <EM>associated values</EM> table stored in a |
+local static array. The associated values table is constructed |
+internally by <CODE>gperf</CODE> and later output as a static local C array |
+called <SAMP>`hash_table'</SAMP>. The relevant selected positions (i.e. indices |
+into <VAR>str</VAR>) are specified via the <SAMP>`-k'</SAMP> option when running |
+<CODE>gperf</CODE>, as detailed in the <EM>Options</EM> section below (see section <A HREF="gperf.html#SEC18">4. Invoking <CODE>gperf</CODE></A>). |
+</DL> |
+ |
+ |
+<P> |
+<DL> |
+<DT><U>Function:</U> <B>in_word_set</B> <I>(const char * <VAR>str</VAR>, unsigned int <VAR>len</VAR>)</I> |
+<DD><A NAME="IDX35"></A> |
+If <VAR>str</VAR> is in the keyword set, returns a pointer to that |
+keyword. More exactly, if the option <SAMP>`-t'</SAMP> (or, equivalently, the |
+<SAMP>`%struct-type'</SAMP> declaration) was given, it returns |
+a pointer to the matching keyword's structure. Otherwise it returns |
+<CODE>NULL</CODE>. |
+</DL> |
+ |
+ |
+<P> |
+If the option <SAMP>`-c'</SAMP> (or, equivalently, the <SAMP>`%compare-strncmp'</SAMP> |
+declaration) is not used, <VAR>str</VAR> must be a NUL terminated |
+string of exactly length <VAR>len</VAR>. If <SAMP>`-c'</SAMP> (or, equivalently, the |
+<SAMP>`%compare-strncmp'</SAMP> declaration) is used, <VAR>str</VAR> must |
+simply be an array of <VAR>len</VAR> bytes and does not need to be NUL |
+terminated. |
+ |
+ |
+<P> |
+The code generated for these two functions is affected by the following |
+options: |
+ |
+ |
+<DL COMPACT> |
+ |
+<DT><SAMP>`-t'</SAMP> |
+<DD> |
+<DT><SAMP>`--struct-type'</SAMP> |
+<DD> |
+Make use of the user-defined <CODE>struct</CODE>. |
+ |
+<DT><SAMP>`-S <VAR>total-switch-statements</VAR>'</SAMP> |
+<DD> |
+<DT><SAMP>`--switch=<VAR>total-switch-statements</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX36"></A> |
+Generate 1 or more C <CODE>switch</CODE> statement rather than use a large, |
+(and potentially sparse) static array. Although the exact time and |
+space savings of this approach vary according to your C compiler's |
+degree of optimization, this method often results in smaller and faster |
+code. |
+</DL> |
+ |
+<P> |
+If the <SAMP>`-t'</SAMP> and <SAMP>`-S'</SAMP> options (or, equivalently, the |
+<SAMP>`%struct-type'</SAMP> and <SAMP>`%switch'</SAMP> declarations) are omitted, the default |
+action |
+is to generate a <CODE>char *</CODE> array containing the keywords, together with |
+additional empty strings used for padding the array. By experimenting |
+with the various input and output options, and timing the resulting C |
+code, you can determine the best option choices for different keyword |
+set characteristics. |
+ |
+ |
+ |
+ |
+<H2><A NAME="SEC17" HREF="gperf.html#TOC17">3.3 Use of NUL bytes</A></H2> |
+<P> |
+<A NAME="IDX37"></A> |
+ |
+ |
+<P> |
+By default, the code generated by <CODE>gperf</CODE> operates on zero |
+terminated strings, the usual representation of strings in C. This means |
+that the keywords in the input file must not contain NUL bytes, |
+and the <VAR>str</VAR> argument passed to <CODE>hash</CODE> or <CODE>in_word_set</CODE> |
+must be NUL terminated and have exactly length <VAR>len</VAR>. |
+ |
+ |
+<P> |
+If option <SAMP>`-c'</SAMP> (or, equivalently, the <SAMP>`%compare-strncmp'</SAMP> |
+declaration) is used, then the <VAR>str</VAR> argument does not need |
+to be NUL terminated. The code generated by <CODE>gperf</CODE> will only |
+access the first <VAR>len</VAR>, not <VAR>len+1</VAR>, bytes starting at <VAR>str</VAR>. |
+However, the keywords in the input file still must not contain NUL |
+bytes. |
+ |
+ |
+<P> |
+If option <SAMP>`-l'</SAMP> (or, equivalently, the <SAMP>`%compare-lengths'</SAMP> |
+declaration) is used, then the hash table performs binary |
+comparison. The keywords in the input file may contain NUL bytes, |
+written in string syntax as <CODE>\000</CODE> or <CODE>\x00</CODE>, and the code |
+generated by <CODE>gperf</CODE> will treat NUL like any other byte. |
+Also, in this case the <SAMP>`-c'</SAMP> option (or, equivalently, the |
+<SAMP>`%compare-strncmp'</SAMP> declaration) is ignored. |
+ |
+ |
+ |
+ |
+<H1><A NAME="SEC18" HREF="gperf.html#TOC18">4. Invoking <CODE>gperf</CODE></A></H1> |
+ |
+<P> |
+There are <EM>many</EM> options to <CODE>gperf</CODE>. They were added to make |
+the program more convenient for use with real applications. "On-line" |
+help is readily available via the <SAMP>`--help'</SAMP> option. Here is the |
+complete list of options. |
+ |
+ |
+ |
+ |
+<H2><A NAME="SEC19" HREF="gperf.html#TOC19">4.1 Specifying the Location of the Output File</A></H2> |
+ |
+<DL COMPACT> |
+ |
+<DT><SAMP>`--output-file=<VAR>file</VAR>'</SAMP> |
+<DD> |
+Allows you to specify the name of the file to which the output is written to. |
+</DL> |
+ |
+<P> |
+The results are written to standard output if no output file is specified |
+or if it is <SAMP>`-'</SAMP>. |
+ |
+ |
+ |
+ |
+<H2><A NAME="SEC20" HREF="gperf.html#TOC20">4.2 Options that affect Interpretation of the Input File</A></H2> |
+ |
+<P> |
+These options are also available as declarations in the input file |
+(see section <A HREF="gperf.html#SEC11">3.1.1.2 Gperf Declarations</A>). |
+ |
+ |
+<DL COMPACT> |
+ |
+<DT><SAMP>`-e <VAR>keyword-delimiter-list</VAR>'</SAMP> |
+<DD> |
+<DT><SAMP>`--delimiters=<VAR>keyword-delimiter-list</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX38"></A> |
+Allows you to provide a string containing delimiters used to |
+separate keywords from their attributes. The default is ",". This |
+option is essential if you want to use keywords that have embedded |
+commas or newlines. One useful trick is to use -e'TAB', where TAB is |
+the literal tab character. |
+ |
+<DT><SAMP>`-t'</SAMP> |
+<DD> |
+<DT><SAMP>`--struct-type'</SAMP> |
+<DD> |
+Allows you to include a <CODE>struct</CODE> type declaration for generated |
+code. Any text before a pair of consecutive <SAMP>`%%'</SAMP> is considered |
+part of the type declaration. Keywords and additional fields may follow |
+this, one group of fields per line. A set of examples for generating |
+perfect hash tables and functions for Ada, C, C++, Pascal, Modula 2, |
+Modula 3 and JavaScript reserved words are distributed with this release. |
+ |
+<DT><SAMP>`--ignore-case'</SAMP> |
+<DD> |
+Consider upper and lower case ASCII characters as equivalent. The string |
+comparison will use a case insignificant character comparison. Note that |
+locale dependent case mappings are ignored. This option is therefore not |
+suitable if a properly internationalized or locale aware case mapping |
+should be used. (For example, in a Turkish locale, the upper case equivalent |
+of the lowercase ASCII letter <SAMP>`i'</SAMP> is the non-ASCII character |
+<SAMP>`capital i with dot above'</SAMP>.) For this case, it is better to apply |
+an uppercase or lowercase conversion on the string before passing it to |
+the <CODE>gperf</CODE> generated function. |
+</DL> |
+ |
+ |
+ |
+<H2><A NAME="SEC21" HREF="gperf.html#TOC21">4.3 Options to specify the Language for the Output Code</A></H2> |
+ |
+<P> |
+These options are also available as declarations in the input file |
+(see section <A HREF="gperf.html#SEC11">3.1.1.2 Gperf Declarations</A>). |
+ |
+ |
+<DL COMPACT> |
+ |
+<DT><SAMP>`-L <VAR>generated-language-name</VAR>'</SAMP> |
+<DD> |
+<DT><SAMP>`--language=<VAR>generated-language-name</VAR>'</SAMP> |
+<DD> |
+Instructs <CODE>gperf</CODE> to generate code in the language specified by the |
+option's argument. Languages handled are currently: |
+ |
+<DL COMPACT> |
+ |
+<DT><SAMP>`KR-C'</SAMP> |
+<DD> |
+Old-style K&R C. This language is understood by old-style C compilers and |
+ANSI C compilers, but ANSI C compilers may flag warnings (or even errors) |
+because of lacking <SAMP>`const'</SAMP>. |
+ |
+<DT><SAMP>`C'</SAMP> |
+<DD> |
+Common C. This language is understood by ANSI C compilers, and also by |
+old-style C compilers, provided that you <CODE>#define const</CODE> to empty |
+for compilers which don't know about this keyword. |
+ |
+<DT><SAMP>`ANSI-C'</SAMP> |
+<DD> |
+ANSI C. This language is understood by ANSI C compilers and C++ compilers. |
+ |
+<DT><SAMP>`C++'</SAMP> |
+<DD> |
+C++. This language is understood by C++ compilers. |
+</DL> |
+ |
+The default is C. |
+ |
+<DT><SAMP>`-a'</SAMP> |
+<DD> |
+This option is supported for compatibility with previous releases of |
+<CODE>gperf</CODE>. It does not do anything. |
+ |
+<DT><SAMP>`-g'</SAMP> |
+<DD> |
+This option is supported for compatibility with previous releases of |
+<CODE>gperf</CODE>. It does not do anything. |
+</DL> |
+ |
+ |
+ |
+<H2><A NAME="SEC22" HREF="gperf.html#TOC22">4.4 Options for fine tuning Details in the Output Code</A></H2> |
+ |
+<P> |
+Most of these options are also available as declarations in the input file |
+(see section <A HREF="gperf.html#SEC11">3.1.1.2 Gperf Declarations</A>). |
+ |
+ |
+<DL COMPACT> |
+ |
+<DT><SAMP>`-K <VAR>slot-name</VAR>'</SAMP> |
+<DD> |
+<DT><SAMP>`--slot-name=<VAR>slot-name</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX39"></A> |
+This option is only useful when option <SAMP>`-t'</SAMP> (or, equivalently, the |
+<SAMP>`%struct-type'</SAMP> declaration) has been given. |
+By default, the program assumes the structure component identifier for |
+the keyword is <SAMP>`name'</SAMP>. This option allows an arbitrary choice of |
+identifier for this component, although it still must occur as the first |
+field in your supplied <CODE>struct</CODE>. |
+ |
+<DT><SAMP>`-F <VAR>initializers</VAR>'</SAMP> |
+<DD> |
+<DT><SAMP>`--initializer-suffix=<VAR>initializers</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX40"></A> |
+This option is only useful when option <SAMP>`-t'</SAMP> (or, equivalently, the |
+<SAMP>`%struct-type'</SAMP> declaration) has been given. |
+It permits to specify initializers for the structure members following |
+<VAR>slot-name</VAR> in empty hash table entries. The list of initializers |
+should start with a comma. By default, the emitted code will |
+zero-initialize structure members following <VAR>slot-name</VAR>. |
+ |
+<DT><SAMP>`-H <VAR>hash-function-name</VAR>'</SAMP> |
+<DD> |
+<DT><SAMP>`--hash-function-name=<VAR>hash-function-name</VAR>'</SAMP> |
+<DD> |
+Allows you to specify the name for the generated hash function. Default |
+name is <SAMP>`hash'</SAMP>. This option permits the use of two hash tables in |
+the same file. |
+ |
+<DT><SAMP>`-N <VAR>lookup-function-name</VAR>'</SAMP> |
+<DD> |
+<DT><SAMP>`--lookup-function-name=<VAR>lookup-function-name</VAR>'</SAMP> |
+<DD> |
+Allows you to specify the name for the generated lookup function. |
+Default name is <SAMP>`in_word_set'</SAMP>. This option permits multiple |
+generated hash functions to be used in the same application. |
+ |
+<DT><SAMP>`-Z <VAR>class-name</VAR>'</SAMP> |
+<DD> |
+<DT><SAMP>`--class-name=<VAR>class-name</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX41"></A> |
+This option is only useful when option <SAMP>`-L C++'</SAMP> (or, equivalently, |
+the <SAMP>`%language=C++'</SAMP> declaration) has been given. It |
+allows you to specify the name of generated C++ class. Default name is |
+<CODE>Perfect_Hash</CODE>. |
+ |
+<DT><SAMP>`-7'</SAMP> |
+<DD> |
+<DT><SAMP>`--seven-bit'</SAMP> |
+<DD> |
+This option specifies that all strings that will be passed as arguments |
+to the generated hash function and the generated lookup function will |
+solely consist of 7-bit ASCII characters (bytes in the range 0..127). |
+(Note that the ANSI C functions <CODE>isalnum</CODE> and <CODE>isgraph</CODE> do |
+<EM>not</EM> guarantee that a byte is in this range. Only an explicit |
+test like <SAMP>`c >= 'A' && c <= 'Z''</SAMP> guarantees this.) This was the |
+default in versions of <CODE>gperf</CODE> earlier than 2.7; now the default is |
+to support 8-bit and multibyte characters. |
+ |
+<DT><SAMP>`-l'</SAMP> |
+<DD> |
+<DT><SAMP>`--compare-lengths'</SAMP> |
+<DD> |
+Compare keyword lengths before trying a string comparison. This option |
+is mandatory for binary comparisons (see section <A HREF="gperf.html#SEC17">3.3 Use of NUL bytes</A>). It also might |
+cut down on the number of string comparisons made during the lookup, since |
+keywords with different lengths are never compared via <CODE>strcmp</CODE>. |
+However, using <SAMP>`-l'</SAMP> might greatly increase the size of the |
+generated C code if the lookup table range is large (which implies that |
+the switch option <SAMP>`-S'</SAMP> or <SAMP>`%switch'</SAMP> is not enabled), since the length |
+table contains as many elements as there are entries in the lookup table. |
+ |
+<DT><SAMP>`-c'</SAMP> |
+<DD> |
+<DT><SAMP>`--compare-strncmp'</SAMP> |
+<DD> |
+Generates C code that uses the <CODE>strncmp</CODE> function to perform |
+string comparisons. The default action is to use <CODE>strcmp</CODE>. |
+ |
+<DT><SAMP>`-C'</SAMP> |
+<DD> |
+<DT><SAMP>`--readonly-tables'</SAMP> |
+<DD> |
+Makes the contents of all generated lookup tables constant, i.e., |
+"readonly". Many compilers can generate more efficient code for this |
+by putting the tables in readonly memory. |
+ |
+<DT><SAMP>`-E'</SAMP> |
+<DD> |
+<DT><SAMP>`--enum'</SAMP> |
+<DD> |
+Define constant values using an enum local to the lookup function rather |
+than with #defines. This also means that different lookup functions can |
+reside in the same file. Thanks to James Clark <CODE><jjc@ai.mit.edu></CODE>. |
+ |
+<DT><SAMP>`-I'</SAMP> |
+<DD> |
+<DT><SAMP>`--includes'</SAMP> |
+<DD> |
+Include the necessary system include file, <CODE><string.h></CODE>, at the |
+beginning of the code. By default, this is not done; the user must |
+include this header file himself to allow compilation of the code. |
+ |
+<DT><SAMP>`-G'</SAMP> |
+<DD> |
+<DT><SAMP>`--global-table'</SAMP> |
+<DD> |
+Generate the static table of keywords as a static global variable, |
+rather than hiding it inside of the lookup function (which is the |
+default behavior). |
+ |
+<DT><SAMP>`-P'</SAMP> |
+<DD> |
+<DT><SAMP>`--pic'</SAMP> |
+<DD> |
+Optimize the generated table for inclusion in shared libraries. This |
+reduces the startup time of programs using a shared library containing |
+the generated code. If the option <SAMP>`-t'</SAMP> (or, equivalently, the |
+<SAMP>`%struct-type'</SAMP> declaration) is also given, the first field of the |
+user-defined struct must be of type <SAMP>`int'</SAMP>, not <SAMP>`char *'</SAMP>, because |
+it will contain offsets into the string pool instead of actual strings. |
+To convert such an offset to a string, you can use the expression |
+<SAMP>`stringpool + <VAR>o</VAR>'</SAMP>, where <VAR>o</VAR> is the offset. The string pool |
+name can be changed through the option <SAMP>`--string-pool-name'</SAMP>. |
+ |
+<DT><SAMP>`-Q <VAR>string-pool-name</VAR>'</SAMP> |
+<DD> |
+<DT><SAMP>`--string-pool-name=<VAR>string-pool-name</VAR>'</SAMP> |
+<DD> |
+Allows you to specify the name of the generated string pool created by |
+option <SAMP>`-P'</SAMP>. The default name is <SAMP>`stringpool'</SAMP>. This option |
+permits the use of two hash tables in the same file, with <SAMP>`-P'</SAMP> and |
+even when the option <SAMP>`-G'</SAMP> (or, equivalently, the <SAMP>`%global-table'</SAMP> |
+declaration) is given. |
+ |
+<DT><SAMP>`--null-strings'</SAMP> |
+<DD> |
+Use NULL strings instead of empty strings for empty keyword table entries. |
+This reduces the startup time of programs using a shared library containing |
+the generated code (but not as much as option <SAMP>`-P'</SAMP>), at the expense |
+of one more test-and-branch instruction at run time. |
+ |
+<DT><SAMP>`-W <VAR>hash-table-array-name</VAR>'</SAMP> |
+<DD> |
+<DT><SAMP>`--word-array-name=<VAR>hash-table-array-name</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX42"></A> |
+Allows you to specify the name for the generated array containing the |
+hash table. Default name is <SAMP>`wordlist'</SAMP>. This option permits the |
+use of two hash tables in the same file, even when the option <SAMP>`-G'</SAMP> |
+(or, equivalently, the <SAMP>`%global-table'</SAMP> declaration) is given. |
+ |
+<DT><SAMP>`-S <VAR>total-switch-statements</VAR>'</SAMP> |
+<DD> |
+<DT><SAMP>`--switch=<VAR>total-switch-statements</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX43"></A> |
+Causes the generated C code to use a <CODE>switch</CODE> statement scheme, |
+rather than an array lookup table. This can lead to a reduction in both |
+time and space requirements for some input files. The argument to this |
+option determines how many <CODE>switch</CODE> statements are generated. A |
+value of 1 generates 1 <CODE>switch</CODE> containing all the elements, a |
+value of 2 generates 2 tables with 1/2 the elements in each |
+<CODE>switch</CODE>, etc. This is useful since many C compilers cannot |
+correctly generate code for large <CODE>switch</CODE> statements. This option |
+was inspired in part by Keith Bostic's original C program. |
+ |
+<DT><SAMP>`-T'</SAMP> |
+<DD> |
+<DT><SAMP>`--omit-struct-type'</SAMP> |
+<DD> |
+Prevents the transfer of the type declaration to the output file. Use |
+this option if the type is already defined elsewhere. |
+ |
+<DT><SAMP>`-p'</SAMP> |
+<DD> |
+This option is supported for compatibility with previous releases of |
+<CODE>gperf</CODE>. It does not do anything. |
+</DL> |
+ |
+ |
+ |
+<H2><A NAME="SEC23" HREF="gperf.html#TOC23">4.5 Options for changing the Algorithms employed by <CODE>gperf</CODE></A></H2> |
+ |
+<DL COMPACT> |
+ |
+<DT><SAMP>`-k <VAR>selected-byte-positions</VAR>'</SAMP> |
+<DD> |
+<DT><SAMP>`--key-positions=<VAR>selected-byte-positions</VAR>'</SAMP> |
+<DD> |
+Allows selection of the byte positions used in the keywords' |
+hash function. The allowable choices range between 1-255, inclusive. |
+The positions are separated by commas, e.g., <SAMP>`-k 9,4,13,14'</SAMP>; |
+ranges may be used, e.g., <SAMP>`-k 2-7'</SAMP>; and positions may occur |
+in any order. Furthermore, the wildcard '*' causes the generated |
+hash function to consider <STRONG>all</STRONG> byte positions in each keyword, |
+whereas '$' instructs the hash function to use the "final byte" |
+of a keyword (this is the only way to use a byte position greater than |
+255, incidentally). |
+ |
+For instance, the option <SAMP>`-k 1,2,4,6-10,'$''</SAMP> generates a hash |
+function that considers positions 1,2,4,6,7,8,9,10, plus the last |
+byte in each keyword (which may be at a different position for each |
+keyword, obviously). Keywords |
+with length less than the indicated byte positions work properly, since |
+selected byte positions exceeding the keyword length are simply not |
+referenced in the hash function. |
+ |
+This option is not normally needed since version 2.8 of <CODE>gperf</CODE>; |
+the default byte positions are computed depending on the keyword set, |
+through a search that minimizes the number of byte positions. |
+ |
+<DT><SAMP>`-D'</SAMP> |
+<DD> |
+<DT><SAMP>`--duplicates'</SAMP> |
+<DD> |
+<A NAME="IDX44"></A> |
+Handle keywords whose selected byte sets hash to duplicate values. |
+Duplicate hash values can occur if a set of keywords has the same names, but |
+possesses different attributes, or if the selected byte positions are not well |
+chosen. With the -D option <CODE>gperf</CODE> treats all these keywords as |
+part of an equivalence class and generates a perfect hash function with |
+multiple comparisons for duplicate keywords. It is up to you to completely |
+disambiguate the keywords by modifying the generated C code. However, |
+<CODE>gperf</CODE> helps you out by organizing the output. |
+ |
+Using this option usually means that the generated hash function is no |
+longer perfect. On the other hand, it permits <CODE>gperf</CODE> to work on |
+keyword sets that it otherwise could not handle. |
+ |
+<DT><SAMP>`-m <VAR>iterations</VAR>'</SAMP> |
+<DD> |
+<DT><SAMP>`--multiple-iterations=<VAR>iterations</VAR>'</SAMP> |
+<DD> |
+Perform multiple choices of the <SAMP>`-i'</SAMP> and <SAMP>`-j'</SAMP> values, and |
+choose the best results. This increases the running time by a factor of |
+<VAR>iterations</VAR> but does a good job minimizing the generated table size. |
+ |
+<DT><SAMP>`-i <VAR>initial-value</VAR>'</SAMP> |
+<DD> |
+<DT><SAMP>`--initial-asso=<VAR>initial-value</VAR>'</SAMP> |
+<DD> |
+Provides an initial <VAR>value</VAR> for the associate values array. Default |
+is 0. Increasing the initial value helps inflate the final table size, |
+possibly leading to more time efficient keyword lookups. Note that this |
+option is not particularly useful when <SAMP>`-S'</SAMP> (or, equivalently, |
+<SAMP>`%switch'</SAMP>) is used. Also, |
+<SAMP>`-i'</SAMP> is overridden when the <SAMP>`-r'</SAMP> option is used. |
+ |
+<DT><SAMP>`-j <VAR>jump-value</VAR>'</SAMP> |
+<DD> |
+<DT><SAMP>`--jump=<VAR>jump-value</VAR>'</SAMP> |
+<DD> |
+<A NAME="IDX45"></A> |
+Affects the "jump value", i.e., how far to advance the associated |
+byte value upon collisions. <VAR>Jump-value</VAR> is rounded up to an |
+odd number, the default is 5. If the <VAR>jump-value</VAR> is 0 <CODE>gperf</CODE> |
+jumps by random amounts. |
+ |
+<DT><SAMP>`-n'</SAMP> |
+<DD> |
+<DT><SAMP>`--no-strlen'</SAMP> |
+<DD> |
+Instructs the generator not to include the length of a keyword when |
+computing its hash value. This may save a few assembly instructions in |
+the generated lookup table. |
+ |
+<DT><SAMP>`-r'</SAMP> |
+<DD> |
+<DT><SAMP>`--random'</SAMP> |
+<DD> |
+Utilizes randomness to initialize the associated values table. This |
+frequently generates solutions faster than using deterministic |
+initialization (which starts all associated values at 0). Furthermore, |
+using the randomization option generally increases the size of the |
+table. |
+ |
+<DT><SAMP>`-s <VAR>size-multiple</VAR>'</SAMP> |
+<DD> |
+<DT><SAMP>`--size-multiple=<VAR>size-multiple</VAR>'</SAMP> |
+<DD> |
+Affects the size of the generated hash table. The numeric argument for |
+this option indicates "how many times larger or smaller" the maximum |
+associated value range should be, in relationship to the number of keywords. |
+It can be written as an integer, a floating-point number or a fraction. |
+For example, a value of 3 means "allow the maximum associated value to be |
+about 3 times larger than the number of input keywords". |
+Conversely, a value of 1/3 means "allow the maximum associated value to |
+be about 3 times smaller than the number of input keywords". Values |
+smaller than 1 are useful for limiting the overall size of the generated hash |
+table, though the option <SAMP>`-m'</SAMP> is better at this purpose. |
+ |
+If `generate switch' option <SAMP>`-S'</SAMP> (or, equivalently, <SAMP>`%switch'</SAMP>) is |
+<EM>not</EM> enabled, the maximum |
+associated value influences the static array table size, and a larger |
+table should decrease the time required for an unsuccessful search, at |
+the expense of extra table space. |
+ |
+The default value is 1, thus the default maximum associated value about |
+the same size as the number of keywords (for efficiency, the maximum |
+associated value is always rounded up to a power of 2). The actual |
+table size may vary somewhat, since this technique is essentially a |
+heuristic. |
+</DL> |
+ |
+ |
+ |
+<H2><A NAME="SEC24" HREF="gperf.html#TOC24">4.6 Informative Output</A></H2> |
+ |
+<DL COMPACT> |
+ |
+<DT><SAMP>`-h'</SAMP> |
+<DD> |
+<DT><SAMP>`--help'</SAMP> |
+<DD> |
+Prints a short summary on the meaning of each program option. Aborts |
+further program execution. |
+ |
+<DT><SAMP>`-v'</SAMP> |
+<DD> |
+<DT><SAMP>`--version'</SAMP> |
+<DD> |
+Prints out the current version number. |
+ |
+<DT><SAMP>`-d'</SAMP> |
+<DD> |
+<DT><SAMP>`--debug'</SAMP> |
+<DD> |
+Enables the debugging option. This produces verbose diagnostics to |
+"standard error" when <CODE>gperf</CODE> is executing. It is useful both for |
+maintaining the program and for determining whether a given set of |
+options is actually speeding up the search for a solution. Some useful |
+information is dumped at the end of the program when the <SAMP>`-d'</SAMP> |
+option is enabled. |
+</DL> |
+ |
+ |
+ |
+<H1><A NAME="SEC25" HREF="gperf.html#TOC25">5. Known Bugs and Limitations with <CODE>gperf</CODE></A></H1> |
+ |
+<P> |
+The following are some limitations with the current release of |
+<CODE>gperf</CODE>: |
+ |
+ |
+ |
+<UL> |
+<LI> |
+ |
+The <CODE>gperf</CODE> utility is tuned to execute quickly, and works quickly |
+for small to medium size data sets (around 1000 keywords). It is |
+extremely useful for maintaining perfect hash functions for compiler |
+keyword sets. Several recent enhancements now enable <CODE>gperf</CODE> to |
+work efficiently on much larger keyword sets (over 15,000 keywords). |
+When processing large keyword sets it helps greatly to have over 8 megs |
+of RAM. |
+ |
+<LI> |
+ |
+The size of the generate static keyword array can get <EM>extremely</EM> |
+large if the input keyword file is large or if the keywords are quite |
+similar. This tends to slow down the compilation of the generated C |
+code, and <EM>greatly</EM> inflates the object code size. If this |
+situation occurs, consider using the <SAMP>`-S'</SAMP> option to reduce data |
+size, potentially increasing keyword recognition time a negligible |
+amount. Since many C compilers cannot correctly generate code for |
+large switch statements it is important to qualify the <VAR>-S</VAR> option |
+with an appropriate numerical argument that controls the number of |
+switch statements generated. |
+ |
+<LI> |
+ |
+The maximum number of selected byte positions has an |
+arbitrary limit of 255. This restriction should be removed, and if |
+anyone considers this a problem write me and let me know so I can remove |
+the constraint. |
+</UL> |
+ |
+ |
+ |
+<H1><A NAME="SEC26" HREF="gperf.html#TOC26">6. Things Still Left to Do</A></H1> |
+ |
+<P> |
+It should be "relatively" easy to replace the current perfect hash |
+function algorithm with a more exhaustive approach; the perfect hash |
+module is essential independent from other program modules. Additional |
+worthwhile improvements include: |
+ |
+ |
+ |
+<UL> |
+<LI> |
+ |
+Another useful extension involves modifying the program to generate |
+"minimal" perfect hash functions (under certain circumstances, the |
+current version can be rather extravagant in the generated table size). |
+This is mostly of theoretical interest, since a sparse table |
+often produces faster lookups, and use of the <SAMP>`-S'</SAMP> <CODE>switch</CODE> |
+option can minimize the data size, at the expense of slightly longer |
+lookups (note that the gcc compiler generally produces good code for |
+<CODE>switch</CODE> statements, reducing the need for more complex schemes). |
+ |
+<LI> |
+ |
+In addition to improving the algorithm, it would also be useful to |
+generate an Ada package as the code output, in addition to the current |
+C and C++ routines. |
+</UL> |
+ |
+ |
+ |
+<H1><A NAME="SEC27" HREF="gperf.html#TOC27">7. Bibliography</A></H1> |
+ |
+<P> |
+[1] Chang, C.C.: <I>A Scheme for Constructing Ordered Minimal Perfect |
+Hashing Functions</I> Information Sciences 39(1986), 187-195. |
+ |
+ |
+<P> |
+[2] Cichelli, Richard J. <I>Author's Response to "On Cichelli's Minimal Perfect Hash |
+Functions Method"</I> Communications of the ACM, 23, 12(December 1980), 729. |
+ |
+ |
+<P> |
+[3] Cichelli, Richard J. <I>Minimal Perfect Hash Functions Made Simple</I> |
+Communications of the ACM, 23, 1(January 1980), 17-19. |
+ |
+ |
+<P> |
+[4] Cook, C. R. and Oldehoeft, R.R. <I>A Letter Oriented Minimal |
+Perfect Hashing Function</I> SIGPLAN Notices, 17, 9(September 1982), 18-27. |
+ |
+ |
+<P> |
+[5] Cormack, G. V. and Horspool, R. N. S. and Kaiserwerth, M. |
+<I>Practical Perfect Hashing</I> Computer Journal, 28, 1(January 1985), 54-58. |
+ |
+ |
+<P> |
+[6] Jaeschke, G. <I>Reciprocal Hashing: A Method for Generating Minimal |
+Perfect Hashing Functions</I> Communications of the ACM, 24, 12(December |
+1981), 829-833. |
+ |
+ |
+<P> |
+[7] Jaeschke, G. and Osterburg, G. <I>On Cichelli's Minimal Perfect |
+Hash Functions Method</I> Communications of the ACM, 23, 12(December 1980), |
+728-729. |
+ |
+ |
+<P> |
+[8] Sager, Thomas J. <I>A Polynomial Time Generator for Minimal Perfect |
+Hash Functions</I> Communications of the ACM, 28, 5(December 1985), 523-532 |
+ |
+ |
+<P> |
+[9] Schmidt, Douglas C. <I>GPERF: A Perfect Hash Function Generator</I> |
+Second USENIX C++ Conference Proceedings, April 1990. |
+ |
+ |
+<P> |
+[10] Schmidt, Douglas C. <I>GPERF: A Perfect Hash Function Generator</I> |
+C++ Report, SIGS 10 10 (November/December 1998). |
+ |
+ |
+<P> |
+[11] Sebesta, R.W. and Taylor, M.A. <I>Minimal Perfect Hash Functions |
+for Reserved Word Lists</I> SIGPLAN Notices, 20, 12(September 1985), 47-53. |
+ |
+ |
+<P> |
+[12] Sprugnoli, R. <I>Perfect Hashing Functions: A Single Probe |
+Retrieving Method for Static Sets</I> Communications of the ACM, 20 |
+11(November 1977), 841-850. |
+ |
+ |
+<P> |
+[13] Stallman, Richard M. <I>Using and Porting GNU CC</I> Free Software Foundation, |
+1988. |
+ |
+ |
+<P> |
+[14] Stroustrup, Bjarne <I>The C++ Programming Language.</I> Addison-Wesley, 1986. |
+ |
+ |
+<P> |
+[15] Tiemann, Michael D. <I>User's Guide to GNU C++</I> Free Software |
+Foundation, 1989. |
+ |
+ |
+ |
+ |
+<H1><A NAME="SEC28" HREF="gperf.html#TOC28">Concept Index</A></H1> |
+ |
+<P> |
+Jump to: |
+<A HREF="#cindex_%">%</A> |
+- |
+<A HREF="#cindex_a">a</A> |
+- |
+<A HREF="#cindex_b">b</A> |
+- |
+<A HREF="#cindex_c">c</A> |
+- |
+<A HREF="#cindex_d">d</A> |
+- |
+<A HREF="#cindex_f">f</A> |
+- |
+<A HREF="#cindex_h">h</A> |
+- |
+<A HREF="#cindex_i">i</A> |
+- |
+<A HREF="#cindex_j">j</A> |
+- |
+<A HREF="#cindex_k">k</A> |
+- |
+<A HREF="#cindex_m">m</A> |
+- |
+<A HREF="#cindex_n">n</A> |
+- |
+<A HREF="#cindex_s">s</A> |
+<P> |
+<H2><A NAME="cindex_%">%</A></H2> |
+<DIR> |
+<LI><A HREF="gperf.html#IDX8"><SAMP>`%%'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX18"><SAMP>`%7bit'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX19"><SAMP>`%compare-lengths'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX20"><SAMP>`%compare-strncmp'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX17"><SAMP>`%define class-name'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX15"><SAMP>`%define hash-function-name'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX14"><SAMP>`%define initializer-suffix'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX16"><SAMP>`%define lookup-function-name'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX13"><SAMP>`%define slot-name'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX26"><SAMP>`%define string-pool-name'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX28"><SAMP>`%define word-array-name'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX9"><SAMP>`%delimiters'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX22"><SAMP>`%enum'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX24"><SAMP>`%global-table'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX11"><SAMP>`%ignore-case'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX23"><SAMP>`%includes'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX12"><SAMP>`%language'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX27"><SAMP>`%null-strings'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX30"><SAMP>`%omit-struct-type'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX25"><SAMP>`%pic'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX21"><SAMP>`%readonly-tables'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX10"><SAMP>`%struct-type'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX29"><SAMP>`%switch'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX31"><SAMP>`%{'</SAMP></A> |
+<LI><A HREF="gperf.html#IDX32"><SAMP>`%}'</SAMP></A> |
+</DIR> |
+<H2><A NAME="cindex_a">a</A></H2> |
+<DIR> |
+<LI><A HREF="gperf.html#IDX42">Array name</A> |
+</DIR> |
+<H2><A NAME="cindex_b">b</A></H2> |
+<DIR> |
+<LI><A HREF="gperf.html#IDX1">Bugs</A> |
+</DIR> |
+<H2><A NAME="cindex_c">c</A></H2> |
+<DIR> |
+<LI><A HREF="gperf.html#IDX41">Class name</A> |
+</DIR> |
+<H2><A NAME="cindex_d">d</A></H2> |
+<DIR> |
+<LI><A HREF="gperf.html#IDX5">Declaration section</A> |
+<LI><A HREF="gperf.html#IDX38">Delimiters</A> |
+<LI><A HREF="gperf.html#IDX44">Duplicates</A> |
+</DIR> |
+<H2><A NAME="cindex_f">f</A></H2> |
+<DIR> |
+<LI><A HREF="gperf.html#IDX4">Format</A> |
+<LI><A HREF="gperf.html#IDX7">Functions section</A> |
+</DIR> |
+<H2><A NAME="cindex_h">h</A></H2> |
+<DIR> |
+<LI><A HREF="gperf.html#IDX34">hash</A> |
+<LI><A HREF="gperf.html#IDX33">hash table</A> |
+</DIR> |
+<H2><A NAME="cindex_i">i</A></H2> |
+<DIR> |
+<LI><A HREF="gperf.html#IDX35">in_word_set</A> |
+<LI><A HREF="gperf.html#IDX40">Initializers</A> |
+</DIR> |
+<H2><A NAME="cindex_j">j</A></H2> |
+<DIR> |
+<LI><A HREF="gperf.html#IDX45">Jump value</A> |
+</DIR> |
+<H2><A NAME="cindex_k">k</A></H2> |
+<DIR> |
+<LI><A HREF="gperf.html#IDX6">Keywords section</A> |
+</DIR> |
+<H2><A NAME="cindex_m">m</A></H2> |
+<DIR> |
+<LI><A HREF="gperf.html#IDX3">Minimal perfect hash functions</A> |
+</DIR> |
+<H2><A NAME="cindex_n">n</A></H2> |
+<DIR> |
+<LI><A HREF="gperf.html#IDX37">NUL</A> |
+</DIR> |
+<H2><A NAME="cindex_s">s</A></H2> |
+<DIR> |
+<LI><A HREF="gperf.html#IDX39">Slot name</A> |
+<LI><A HREF="gperf.html#IDX2">Static search structure</A> |
+<LI><A HREF="gperf.html#IDX36"><CODE>switch</CODE></A>, <A HREF="gperf.html#IDX43"><CODE>switch</CODE></A> |
+</DIR> |
+ |
+ |
+<P><HR><P> |
+This document was generated on 12 June 2003 using |
+<A HREF="http://wwwinfo.cern.ch/dis/texi2html/">texi2html</A> 1.56k. |
+</BODY> |
+</HTML> |
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