Fast algorithm for double->string conversion.

src/conversions.cc

Index: src/conversions.cc
===================================================================
--- src/conversions.cc	(revision 3886)
+++ src/conversions.cc	(working copy)
@@ -25,12 +25,14 @@
 // (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 {
@@ -382,8 +384,17 @@
       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('-');
 
@@ -418,7 +429,7 @@
         builder.AddFormatted("%d", exponent);
       }
 
-      freedtoa(decimal_rep);
+      if (used_dtoa) freedtoa(decimal_rep);
     }
   }
   return builder.Finalize();
@@ -552,9 +563,18 @@
   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);
   }
@@ -567,7 +587,7 @@
   char* result =
       CreateExponentialRepresentation(decimal_rep, exponent, negative, f+1);
 
-  freedtoa(decimal_rep);
+  if (used_dtoa) freedtoa(decimal_rep);
 
   return result;
 }