1// Copyright 2011 the V8 project authors. All rights reserved.
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27
28#ifndef V8_FAST_DTOA_H_
29#define V8_FAST_DTOA_H_
30
31namespace v8 {
32namespace internal {
33
34enum FastDtoaMode {
35  // Computes the shortest representation of the given input. The returned
36  // result will be the most accurate number of this length. Longer
37  // representations might be more accurate.
38  FAST_DTOA_SHORTEST,
39  // Computes a representation where the precision (number of digits) is
40  // given as input. The precision is independent of the decimal point.
41  FAST_DTOA_PRECISION
42};
43
44// FastDtoa will produce at most kFastDtoaMaximalLength digits. This does not
45// include the terminating '\0' character.
46const int kFastDtoaMaximalLength = 17;
47
48// Provides a decimal representation of v.
49// The result should be interpreted as buffer * 10^(point - length).
50//
51// Precondition:
52//   * v must be a strictly positive finite double.
53//
54// Returns true if it succeeds, otherwise the result can not be trusted.
55// There will be *length digits inside the buffer followed by a null terminator.
56// If the function returns true and mode equals
57//   - FAST_DTOA_SHORTEST, then
58//     the parameter requested_digits is ignored.
59//     The result satisfies
60//         v == (double) (buffer * 10^(point - length)).
61//     The digits in the buffer are the shortest representation possible. E.g.
62//     if 0.099999999999 and 0.1 represent the same double then "1" is returned
63//     with point = 0.
64//     The last digit will be closest to the actual v. That is, even if several
65//     digits might correctly yield 'v' when read again, the buffer will contain
66//     the one closest to v.
67//   - FAST_DTOA_PRECISION, then
68//     the buffer contains requested_digits digits.
69//     the difference v - (buffer * 10^(point-length)) is closest to zero for
70//     all possible representations of requested_digits digits.
71//     If there are two values that are equally close, then FastDtoa returns
72//     false.
73// For both modes the buffer must be large enough to hold the result.
74bool FastDtoa(double d,
75              FastDtoaMode mode,
76              int requested_digits,
77              Vector<char> buffer,
78              int* length,
79              int* decimal_point);
80
81} }  // namespace v8::internal
82
83#endif  // V8_FAST_DTOA_H_
84