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

Revision 18191, 2.7 KB checked in by ghudson, 22 years ago (diff) |
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1 | /* mpz_congruent_ui_p -- test congruence of mpz and ulong. |

2 | |

3 | Copyright 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 | /* There's some explicit checks for c<d since it seems reasonably likely an |

28 | application might use that in a test. |

29 | |

30 | Hopefully the compiler can generate something good for r==(c%d), though |

31 | if modexact is being used exclusively then that's not reached. */ |

32 | |

33 | int |

34 | mpz_congruent_ui_p (mpz_srcptr a, unsigned long cu, unsigned long du) |

35 | { |

36 | mp_srcptr ap; |

37 | mp_size_t asize; |

38 | mp_limb_t c, d, r; |

39 | |

40 | if (du == 0) |

41 | DIVIDE_BY_ZERO; |

42 | |

43 | asize = SIZ(a); |

44 | if (asize == 0) |

45 | { |

46 | if (cu < du) |

47 | return cu == 0; |

48 | else |

49 | return (cu % du) == 0; |

50 | } |

51 | |

52 | /* For nails don't try to be clever if c or d is bigger than a limb, just |

53 | fake up some mpz_t's and go to the main mpz_congruent_p. */ |

54 | if (du > GMP_NUMB_MAX || cu > GMP_NUMB_MAX) |

55 | { |

56 | mp_limb_t climbs[2], dlimbs[2]; |

57 | mpz_t cz, dz; |

58 | |

59 | ALLOC(cz) = 2; |

60 | PTR(cz) = climbs; |

61 | ALLOC(dz) = 2; |

62 | PTR(dz) = dlimbs; |

63 | |

64 | mpz_set_ui (cz, cu); |

65 | mpz_set_ui (dz, du); |

66 | return mpz_congruent_p (a, cz, dz); |

67 | } |

68 | |

69 | /* NEG_MOD works on limbs, so convert ulong to limb */ |

70 | c = cu; |

71 | d = du; |

72 | |

73 | if (asize < 0) |

74 | { |

75 | asize = -asize; |

76 | NEG_MOD (c, c, d); |

77 | } |

78 | |

79 | ap = PTR (a); |

80 | |

81 | if (BELOW_THRESHOLD (asize, MODEXACT_1_ODD_THRESHOLD)) |

82 | { |

83 | r = mpn_mod_1 (ap, asize, d); |

84 | if (c < d) |

85 | return r == c; |

86 | else |

87 | return r == (c % d); |

88 | } |

89 | |

90 | if ((d & 1) == 0) |

91 | { |

92 | /* Strip low zero bits to get odd d required by modexact. If |

93 | d==e*2^n then a==c mod d if and only if both a==c mod 2^n |

94 | and a==c mod e. */ |

95 | |

96 | unsigned twos; |

97 | |

98 | if ((ap[0]-c) & LOW_ZEROS_MASK (d)) |

99 | return 0; |

100 | |

101 | count_trailing_zeros (twos, d); |

102 | d >>= twos; |

103 | } |

104 | |

105 | r = mpn_modexact_1c_odd (ap, asize, d, c); |

106 | return r == 0 || r == d; |

107 | } |

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