Fast algorithm for double->string conversion.

src/conversions.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
 //       with the distribution.
 //     * Neither the name of Google Inc. nor the names of its
 //       contributors may be used to endorse or promote products derived
 //       from this software without specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+#include <math.h>
 #include <stdarg.h>
 
 #include "v8.h"
 
 #include "conversions-inl.h"
 #include "factory.h"
+#include "grisu3.h"
 #include "scanner.h"
 
 namespace v8 {
 namespace internal {
 
 int HexValue(uc32 c) {
   if ('0' <= c && c <= '9')
     return c - '0';
   if ('a' <= c && c <= 'f')
     return c - 'a' + 10;
@@ skipping 331 matching lines @@
       break;
 
     case FP_ZERO:
       builder.AddCharacter('0');
       break;
 
     default: {
       int decimal_point;
       int sign;
 
-      char* decimal_rep = dtoa(v, 0, 0, &decimal_point, &sign, NULL);
-      int length = StrLength(decimal_rep);
+      char* decimal_rep;
+      bool used_dtoa = false;
+      char grisu_buffer[kGrisu3MaximalLength + 1];
+      int length;
+      if (grisu3(v, grisu_buffer, &sign, &length, &decimal_point)) {
+        decimal_rep = &grisu_buffer[0];
+      } else {
+        decimal_rep = dtoa(v, 0, 0, &decimal_point, &sign, NULL);
+        used_dtoa = true;
+        length = StrLength(decimal_rep);
+      }
 
       if (sign) builder.AddCharacter('-');
 
       if (length <= decimal_point && decimal_point <= 21) {
         // ECMA-262 section 9.8.1 step 6.
         builder.AddString(decimal_rep);
         builder.AddPadding('0', decimal_point - length);
 
       } else if (0 < decimal_point && decimal_point <= 21) {
         // ECMA-262 section 9.8.1 step 7.
@@ skipping 14 matching lines @@
           builder.AddCharacter('.');
           builder.AddString(decimal_rep + 1);
         }
         builder.AddCharacter('e');
         builder.AddCharacter((decimal_point >= 0) ? '+' : '-');
         int exponent = decimal_point - 1;
         if (exponent < 0) exponent = -exponent;
         builder.AddFormatted("%d", exponent);
       }
 
-      freedtoa(decimal_rep);
+      if (used_dtoa) freedtoa(decimal_rep);
     }
   }
   return builder.Finalize();
 }
 
 
 const char* IntToCString(int n, Vector<char> buffer) {
   bool negative = false;
   if (n < 0) {
     // We must not negate the most negative int.
@@ skipping 113 matching lines @@
   bool negative = false;
   if (value < 0) {
     value = -value;
     negative = true;
   }
 
   // Find a sufficiently precise decimal representation of n.
   int decimal_point;
   int sign;
   char* decimal_rep = NULL;
+  bool used_dtoa = true;
+  char grisu_buffer[kGrisu3MaximalLength + 1];
   if (f == -1) {
-    decimal_rep = dtoa(value, 0, 0, &decimal_point, &sign, NULL);
-    f = StrLength(decimal_rep) - 1;
+    int length;
+    if (grisu3(value, grisu_buffer, &sign, &length, &decimal_point)) {
+      used_dtoa = false;
+      decimal_rep = &grisu_buffer[0];
+      f = length - 1;
+    } else {
+      decimal_rep = dtoa(value, 0, 0, &decimal_point, &sign, NULL);
+      f = StrLength(decimal_rep) - 1;
+    }
   } else {
     decimal_rep = dtoa(value, 2, f + 1, &decimal_point, &sign, NULL);
   }
   int decimal_rep_length = StrLength(decimal_rep);
   ASSERT(decimal_rep_length > 0);
   ASSERT(decimal_rep_length <= f + 1);
   USE(decimal_rep_length);
 
   int exponent = decimal_point - 1;
   char* result =
       CreateExponentialRepresentation(decimal_rep, exponent, negative, f+1);
 
-  freedtoa(decimal_rep);
+  if (used_dtoa) freedtoa(decimal_rep);
 
   return result;
 }
 
 
 char* DoubleToPrecisionCString(double value, int p) {
   ASSERT(p >= 1 && p <= 21);
 
   bool negative = false;
   if (value < 0) {
@@ skipping 119 matching lines @@
   // Allocate result and fill in the parts.
   StringBuilder builder(result_size + 1);
   builder.AddSubstring(integer_buffer + integer_pos + 1, integer_part_size);
   if (decimal_pos > 0) builder.AddCharacter('.');
   builder.AddSubstring(decimal_buffer, decimal_pos);
   return builder.Finalize();
 }
 
 
 } }  // namespace v8::internal