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1 // Copyright 2011 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #ifndef V8_FAST_DTOA_H_
6 #define V8_FAST_DTOA_H_
7 
8 #include "src/vector.h"
9 
10 namespace v8 {
11 namespace internal {
12 
13 enum FastDtoaMode {
14   // Computes the shortest representation of the given input. The returned
15   // result will be the most accurate number of this length. Longer
16   // representations might be more accurate.
17   FAST_DTOA_SHORTEST,
18   // Computes a representation where the precision (number of digits) is
19   // given as input. The precision is independent of the decimal point.
20   FAST_DTOA_PRECISION
21 };
22 
23 // FastDtoa will produce at most kFastDtoaMaximalLength digits. This does not
24 // include the terminating '\0' character.
25 const int kFastDtoaMaximalLength = 17;
26 
27 // Provides a decimal representation of v.
28 // The result should be interpreted as buffer * 10^(point - length).
29 //
30 // Precondition:
31 //   * v must be a strictly positive finite double.
32 //
33 // Returns true if it succeeds, otherwise the result can not be trusted.
34 // There will be *length digits inside the buffer followed by a null terminator.
35 // If the function returns true and mode equals
36 //   - FAST_DTOA_SHORTEST, then
37 //     the parameter requested_digits is ignored.
38 //     The result satisfies
39 //         v == (double) (buffer * 10^(point - length)).
40 //     The digits in the buffer are the shortest representation possible. E.g.
41 //     if 0.099999999999 and 0.1 represent the same double then "1" is returned
42 //     with point = 0.
43 //     The last digit will be closest to the actual v. That is, even if several
44 //     digits might correctly yield 'v' when read again, the buffer will contain
45 //     the one closest to v.
46 //   - FAST_DTOA_PRECISION, then
47 //     the buffer contains requested_digits digits.
48 //     the difference v - (buffer * 10^(point-length)) is closest to zero for
49 //     all possible representations of requested_digits digits.
50 //     If there are two values that are equally close, then FastDtoa returns
51 //     false.
52 // For both modes the buffer must be large enough to hold the result.
53 bool FastDtoa(double d,
54               FastDtoaMode mode,
55               int requested_digits,
56               Vector<char> buffer,
57               int* length,
58               int* decimal_point);
59 
60 }  // namespace internal
61 }  // namespace v8
62 
63 #endif  // V8_FAST_DTOA_H_
64