bignum-dtoa.h 4.2 KB

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  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. //
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  27. #ifndef DOUBLE_CONVERSION_BIGNUM_DTOA_H_
  28. #define DOUBLE_CONVERSION_BIGNUM_DTOA_H_
  29. #include "utils.h"
  30. namespace double_conversion {
  31. enum BignumDtoaMode {
  32. // Return the shortest correct representation.
  33. // For example the output of 0.299999999999999988897 is (the less accurate but
  34. // correct) 0.3.
  35. BIGNUM_DTOA_SHORTEST,
  36. // Same as BIGNUM_DTOA_SHORTEST but for single-precision floats.
  37. BIGNUM_DTOA_SHORTEST_SINGLE,
  38. // Return a fixed number of digits after the decimal point.
  39. // For instance fixed(0.1, 4) becomes 0.1000
  40. // If the input number is big, the output will be big.
  41. BIGNUM_DTOA_FIXED,
  42. // Return a fixed number of digits, no matter what the exponent is.
  43. BIGNUM_DTOA_PRECISION
  44. };
  45. // Converts the given double 'v' to ascii.
  46. // The result should be interpreted as buffer * 10^(point-length).
  47. // The buffer will be null-terminated.
  48. //
  49. // The input v must be > 0 and different from NaN, and Infinity.
  50. //
  51. // The output depends on the given mode:
  52. // - SHORTEST: produce the least amount of digits for which the internal
  53. // identity requirement is still satisfied. If the digits are printed
  54. // (together with the correct exponent) then reading this number will give
  55. // 'v' again. The buffer will choose the representation that is closest to
  56. // 'v'. If there are two at the same distance, than the number is round up.
  57. // In this mode the 'requested_digits' parameter is ignored.
  58. // - FIXED: produces digits necessary to print a given number with
  59. // 'requested_digits' digits after the decimal point. The produced digits
  60. // might be too short in which case the caller has to fill the gaps with '0's.
  61. // Example: toFixed(0.001, 5) is allowed to return buffer="1", point=-2.
  62. // Halfway cases are rounded up. The call toFixed(0.15, 2) thus returns
  63. // buffer="2", point=0.
  64. // Note: the length of the returned buffer has no meaning wrt the significance
  65. // of its digits. That is, just because it contains '0's does not mean that
  66. // any other digit would not satisfy the internal identity requirement.
  67. // - PRECISION: produces 'requested_digits' where the first digit is not '0'.
  68. // Even though the length of produced digits usually equals
  69. // 'requested_digits', the function is allowed to return fewer digits, in
  70. // which case the caller has to fill the missing digits with '0's.
  71. // Halfway cases are again rounded up.
  72. // 'BignumDtoa' expects the given buffer to be big enough to hold all digits
  73. // and a terminating null-character.
  74. void BignumDtoa(double v, BignumDtoaMode mode, int requested_digits,
  75. Vector<char> buffer, int* length, int* point);
  76. } // namespace double_conversion
  77. #endif // DOUBLE_CONVERSION_BIGNUM_DTOA_H_