Fast algorithm for double->string conversion.

src/grisu3.h

+// Copyright 2010 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.
+
+#ifndef V8_GRISU3_H_
+#define V8_GRISU3_H_
+
+namespace v8 {
+namespace internal {
+
+// Grisu3 will produce at most kGrisu3MaximalLength digits. This does not
+// include the terminating '\0' character.
+static const int kGrisu3MaximalLength = 17;
+
+// Provides a decimal representation of v.
+//   v must satisfy v != 0 and it must not be Infinity or NaN.
+// Returns true if it succeeds, otherwise the result can not be trusted.
+// There will be *length digits inside the buffer followed by a null terminator.
+// If the function returns true then
+//   v == (double) (buffer * 10^(decimal-point - length)).
+// The digits in the buffer are the shortest representation possible: no
+// 0.099999999999 instead of 0.1.
+// The last digit will be closest to the actual v. That is, even if several
+// digits might correctly yield 'v' when read again, the buffer will contain the
+// one closest to v.
+// The variable 'sign' will be '0' if the given number is positive, and '1'
+//   otherwise.
+bool grisu3(double d, char* buffer, int* sign, int* length, int* decimal_point);
+
+} }  // namespace v8::internal
+
+#endif  // V8_GRISU3_H_