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_DTOA_H_
6 #define V8_DTOA_H_
7 
8 #include "src/vector.h"
9 
10 namespace v8 {
11 namespace internal {
12 
13 enum DtoaMode {
14   // Return the shortest correct representation.
15   // For example the output of 0.299999999999999988897 is (the less accurate but
16   // correct) 0.3.
17   DTOA_SHORTEST,
18   // Return a fixed number of digits after the decimal point.
19   // For instance fixed(0.1, 4) becomes 0.1000
20   // If the input number is big, the output will be big.
21   DTOA_FIXED,
22   // Return a fixed number of digits, no matter what the exponent is.
23   DTOA_PRECISION
24 };
25 
26 // The maximal length of digits a double can have in base 10.
27 // Note that DoubleToAscii null-terminates its input. So the given buffer should
28 // be at least kBase10MaximalLength + 1 characters long.
29 const int kBase10MaximalLength = 17;
30 
31 // Converts the given double 'v' to ASCII.
32 // The result should be interpreted as buffer * 10^(point-length).
33 //
34 // The output depends on the given mode:
35 //  - SHORTEST: produce the least amount of digits for which the internal
36 //   identity requirement is still satisfied. If the digits are printed
37 //   (together with the correct exponent) then reading this number will give
38 //   'v' again. The buffer will choose the representation that is closest to
39 //   'v'. If there are two at the same distance, than the one farther away
40 //   from 0 is chosen (halfway cases - ending with 5 - are rounded up).
41 //   In this mode the 'requested_digits' parameter is ignored.
42 //  - FIXED: produces digits necessary to print a given number with
43 //   'requested_digits' digits after the decimal point. The produced digits
44 //   might be too short in which case the caller has to fill the gaps with '0's.
45 //   Example: toFixed(0.001, 5) is allowed to return buffer="1", point=-2.
46 //   Halfway cases are rounded towards +/-Infinity (away from 0). The call
47 //   toFixed(0.15, 2) thus returns buffer="2", point=0.
48 //   The returned buffer may contain digits that would be truncated from the
49 //   shortest representation of the input.
50 //  - PRECISION: produces 'requested_digits' where the first digit is not '0'.
51 //   Even though the length of produced digits usually equals
52 //   'requested_digits', the function is allowed to return fewer digits, in
53 //   which case the caller has to fill the missing digits with '0's.
54 //   Halfway cases are again rounded away from 0.
55 // 'DoubleToAscii' expects the given buffer to be big enough to hold all digits
56 // and a terminating null-character. In SHORTEST-mode it expects a buffer of
57 // at least kBase10MaximalLength + 1. Otherwise, the size of the output is
58 // limited to requested_digits digits plus the null terminator.
59 void DoubleToAscii(double v, DtoaMode mode, int requested_digits,
60                    Vector<char> buffer, int* sign, int* length, int* point);
61 
62 }  // namespace internal
63 }  // namespace v8
64 
65 #endif  // V8_DTOA_H_
66