mfbt/double-conversion/fast-dtoa.h

   1 // Copyright 2010 the V8 project authors. All rights reserved.
   2 // Redistribution and use in source and binary forms, with or without
   3 // modification, are permitted provided that the following conditions are
   4 // met:
   5 //
   6 //     * Redistributions of source code must retain the above copyright
   7 //       notice, this list of conditions and the following disclaimer.
   8 //     * Redistributions in binary form must reproduce the above
   9 //       copyright notice, this list of conditions and the following
  10 //       disclaimer in the documentation and/or other materials provided
  11 //       with the distribution.
  12 //     * Neither the name of Google Inc. nor the names of its
  13 //       contributors may be used to endorse or promote products derived
  14 //       from this software without specific prior written permission.
  15 //
  16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  18 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  19 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  20 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  21 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  22 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27
  28 #ifndef DOUBLE_CONVERSION_FAST_DTOA_H_
  29 #define DOUBLE_CONVERSION_FAST_DTOA_H_
  30
  31 #include "utils.h"
  32
  33 namespace double_conversion {
  34
  35 enum FastDtoaMode {
  36   // Computes the shortest representation of the given input. The returned
  37   // result will be the most accurate number of this length. Longer
  38   // representations might be more accurate.
  39   FAST_DTOA_SHORTEST,
  40   // Same as FAST_DTOA_SHORTEST but for single-precision floats.
  41   FAST_DTOA_SHORTEST_SINGLE,
  42   // Computes a representation where the precision (number of digits) is
  43   // given as input. The precision is independent of the decimal point.
  44   FAST_DTOA_PRECISION
  45 };
  46
  47 // FastDtoa will produce at most kFastDtoaMaximalLength digits. This does not
  48 // include the terminating '\0' character.
  49 static const int kFastDtoaMaximalLength = 17;
  50 // Same for single-precision numbers.
  51 static const int kFastDtoaMaximalSingleLength = 9;
  52
  53 // Provides a decimal representation of v.
  54 // The result should be interpreted as buffer * 10^(point - length).
  55 //
  56 // Precondition:
  57 //   * v must be a strictly positive finite double.
  58 //
  59 // Returns true if it succeeds, otherwise the result can not be trusted.
  60 // There will be *length digits inside the buffer followed by a null terminator.
  61 // If the function returns true and mode equals
  62 //   - FAST_DTOA_SHORTEST, then
  63 //     the parameter requested_digits is ignored.
  64 //     The result satisfies
  65 //         v == (double) (buffer * 10^(point - length)).
  66 //     The digits in the buffer are the shortest representation possible. E.g.
  67 //     if 0.099999999999 and 0.1 represent the same double then "1" is returned
  68 //     with point = 0.
  69 //     The last digit will be closest to the actual v. That is, even if several
  70 //     digits might correctly yield 'v' when read again, the buffer will contain
  71 //     the one closest to v.
  72 //   - FAST_DTOA_PRECISION, then
  73 //     the buffer contains requested_digits digits.
  74 //     the difference v - (buffer * 10^(point-length)) is closest to zero for
  75 //     all possible representations of requested_digits digits.
  76 //     If there are two values that are equally close, then FastDtoa returns
  77 //     false.
  78 // For both modes the buffer must be large enough to hold the result.
  79 bool FastDtoa(double d,
  80               FastDtoaMode mode,
  81               int requested_digits,
  82               Vector<char> buffer,
  83               int* length,
  84               int* decimal_point);
  85
  86 }  // namespace double_conversion
  87
  88 #endif  // DOUBLE_CONVERSION_FAST_DTOA_H_