dtoa.h revision 25f6136652d8341ed047e7fc1a450af5bd218ea9 
1// Copyright 2010 the V8 project authors. All rights reserved.
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27
28#ifndef V8_DTOA_H_
29#define V8_DTOA_H_
30
31namespace v8 {
32namespace internal {
33
34enum DtoaMode {
35  // 0.9999999999999999 becomes 0.1
36  DTOA_SHORTEST,
37  // Fixed number of digits after the decimal point.
38  // For instance fixed(0.1, 4) becomes 0.1000
39  // If the input number is big, the output will be big.
40  DTOA_FIXED,
41  // Fixed number of digits (independent of the decimal point).
42  DTOA_PRECISION
43};
44
45// The maximal length of digits a double can have in base 10.
46// Note that DoubleToAscii null-terminates its input. So the given buffer should
47// be at least kBase10MaximalLength + 1 characters long.
48static const int kBase10MaximalLength = 17;
49
50// Converts the given double 'v' to ascii.
51// The result should be interpreted as buffer * 10^(point-length).
52//
53// The output depends on the given mode:
54//  - SHORTEST: produce the least amount of digits for which the internal
55//   identity requirement is still satisfied. If the digits are printed
56//   (together with the correct exponent) then reading this number will give
57//   'v' again. The buffer will choose the representation that is closest to
58//   'v'. If there are two at the same distance, than the one farther away
59//   from 0 is chosen (halfway cases - ending with 5 - are rounded up).
60//   In this mode the 'requested_digits' parameter is ignored.
61//  - FIXED: produces digits necessary to print a given number with
62//   'requested_digits' digits after the decimal point. The produced digits
63//   might be too short in which case the caller has to fill the gaps with '0's.
64//   Example: toFixed(0.001, 5) is allowed to return buffer="1", point=-2.
65//   Halfway cases are rounded towards +/-Infinity (away from 0). The call
66//   toFixed(0.15, 2) thus returns buffer="2", point=0.
67//   The returned buffer may contain digits that would be truncated from the
68//   shortest representation of the input.
69//  - PRECISION: produces 'requested_digits' where the first digit is not '0'.
70//   Even though the length of produced digits usually equals
71//   'requested_digits', the function is allowed to return fewer digits, in
72//   which case the caller has to fill the missing digits with '0's.
73//   Halfway cases are again rounded away from 0.
74// 'DoubleToAscii' expects the given buffer to be big enough to hold all digits
75// and a terminating null-character.
76bool DoubleToAscii(double v, DtoaMode mode, int requested_digits,
77                   Vector<char> buffer, int* sign, int* length, int* point);
78
79} }  // namespace v8::internal
80
81#endif  // V8_DTOA_H_
82