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source:
trunk/third/gmp/mpz/get_d.c
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18191

Revision 18191, 2.9 KB checked in by ghudson, 22 years ago (diff) |
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1 | /* double mpz_get_d (mpz_t src) -- Return the double approximation to SRC. |

2 | |

3 | Copyright 1996, 1997, 2000, 2001, 2002 Free Software Foundation, Inc. |

4 | |

5 | This file is part of the GNU MP Library. |

6 | |

7 | The GNU MP Library is free software; you can redistribute it and/or modify |

8 | it under the terms of the GNU Lesser General Public License as published by |

9 | the Free Software Foundation; either version 2.1 of the License, or (at your |

10 | option) any later version. |

11 | |

12 | The GNU MP Library is distributed in the hope that it will be useful, but |

13 | WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |

14 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public |

15 | License for more details. |

16 | |

17 | You should have received a copy of the GNU Lesser General Public License |

18 | along with the GNU MP Library; see the file COPYING.LIB. If not, write to |

19 | the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |

20 | MA 02111-1307, USA. */ |

21 | |

22 | #include "gmp.h" |

23 | #include "gmp-impl.h" |

24 | #include "longlong.h" |

25 | |

26 | |

27 | /* FIXME: Would prefer to inline this on all compilers, not just those with |

28 | "inline". */ |

29 | static inline int |

30 | mpn_zero_p (mp_srcptr p, mp_size_t n) |

31 | { |

32 | mp_size_t i; |

33 | |

34 | for (i = 0; i < n; i++) |

35 | if (p[i] != 0) |

36 | return 0; |

37 | |

38 | return 1; |

39 | } |

40 | |

41 | |

42 | double |

43 | mpz_get_d (mpz_srcptr src) |

44 | { |

45 | double res; |

46 | mp_size_t size; |

47 | int negative; |

48 | mp_ptr qp; |

49 | mp_limb_t hz, lz; |

50 | int cnt; |

51 | |

52 | size = SIZ(src); |

53 | if (size == 0) |

54 | return 0.0; |

55 | |

56 | negative = size < 0; |

57 | size = ABS (size); |

58 | qp = PTR(src); |

59 | |

60 | if (size == 1) |

61 | { |

62 | res = qp[size - 1]; |

63 | } |

64 | else if (size == 2) |

65 | { |

66 | res = MP_BASE_AS_DOUBLE * qp[size - 1] + qp[size - 2]; |

67 | } |

68 | else |

69 | { |

70 | count_leading_zeros (cnt, qp[size - 1]); |

71 | cnt -= GMP_NAIL_BITS; |

72 | |

73 | #if BITS_PER_MP_LIMB == 32 |

74 | if (cnt == 0) |

75 | { |

76 | hz = qp[size - 1]; |

77 | lz = qp[size - 2]; |

78 | } |

79 | else |

80 | { |

81 | hz = ((qp[size - 1] << cnt) | (qp[size - 2] >> GMP_NUMB_BITS - cnt)) & GMP_NUMB_MASK; |

82 | lz = ((qp[size - 2] << cnt) | (qp[size - 3] >> GMP_NUMB_BITS - cnt)) & GMP_NUMB_MASK; |

83 | } |

84 | #if _GMP_IEEE_FLOATS |

85 | /* Take bits from less significant limbs, but only if they may affect |

86 | the result. */ |

87 | if ((lz & 0x7ff) == 0x400) |

88 | { |

89 | if (cnt != 0) |

90 | lz += (((qp[size - 3] << cnt) & GMP_NUMB_MASK) != 0 |

91 | || ! mpn_zero_p (qp, size - 3)); |

92 | else |

93 | lz += (! mpn_zero_p (qp, size - 2)); |

94 | } |

95 | #endif |

96 | res = MP_BASE_AS_DOUBLE * hz + lz; |

97 | res = __gmp_scale2 (res, (size - 2) * GMP_NUMB_BITS - cnt); |

98 | #endif |

99 | #if BITS_PER_MP_LIMB == 64 |

100 | if (cnt == 0) |

101 | hz = qp[size - 1]; |

102 | else |

103 | hz = ((qp[size - 1] << cnt) | (qp[size - 2] >> GMP_NUMB_BITS - cnt)) & GMP_NUMB_MASK; |

104 | #if _GMP_IEEE_FLOATS |

105 | if ((hz & 0x7ff) == 0x400) |

106 | { |

107 | if (cnt != 0) |

108 | hz += (((qp[size - 2] << cnt) & GMP_NUMB_MASK) != 0 |

109 | || ! mpn_zero_p (qp, size - 2)); |

110 | else |

111 | hz += (! mpn_zero_p (qp, size - 1)); |

112 | } |

113 | #endif |

114 | res = hz; |

115 | res = __gmp_scale2 (res, (size - 1) * GMP_NUMB_BITS - cnt); |

116 | #endif |

117 | } |

118 | |

119 | return negative ? -res : res; |

120 | } |

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