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

Revision 18191, 2.4 KB checked in by ghudson, 22 years ago (diff) |
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1 | /* mpz_kronecker_ui -- mpz+ulong Kronecker/Jacobi symbol. |

2 | |

3 | Copyright 1999, 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 | /* This implementation depends on BITS_PER_MP_LIMB being even, so that |

28 | (a/2)^BITS_PER_MP_LIMB = 1 and so there's no need to pay attention to how |

29 | many low zero limbs are stripped. */ |

30 | #if BITS_PER_MP_LIMB % 2 != 0 |

31 | Error, error, unsupported BITS_PER_MP_LIMB |

32 | #endif |

33 | |

34 | |

35 | int |

36 | mpz_kronecker_ui (mpz_srcptr a, unsigned long b) |

37 | { |

38 | mp_srcptr a_ptr = PTR(a); |

39 | mp_size_t a_size; |

40 | mp_limb_t a_rem; |

41 | int result_bit1; |

42 | |

43 | a_size = SIZ(a); |

44 | if (a_size == 0) |

45 | return JACOBI_0U (b); |

46 | |

47 | if (b > GMP_NUMB_MAX) |

48 | { |

49 | mp_limb_t blimbs[2]; |

50 | mpz_t bz; |

51 | ALLOC(bz) = numberof (blimbs); |

52 | PTR(bz) = blimbs; |

53 | mpz_set_ui (bz, b); |

54 | return mpz_kronecker (a, bz); |

55 | } |

56 | |

57 | if ((b & 1) != 0) |

58 | { |

59 | result_bit1 = JACOBI_ASGN_SU_BIT1 (a_size, b); |

60 | } |

61 | else |

62 | { |

63 | mp_limb_t a_low = a_ptr[0]; |

64 | int twos; |

65 | |

66 | if (b == 0) |

67 | return JACOBI_LS0 (a_low, a_size); /* (a/0) */ |

68 | |

69 | if (! (a_low & 1)) |

70 | return 0; /* (even/even)=0 */ |

71 | |

72 | /* (a/2)=(2/a) for a odd */ |

73 | count_trailing_zeros (twos, b); |

74 | b >>= twos; |

75 | result_bit1 = (JACOBI_TWOS_U_BIT1 (twos, a_low) |

76 | ^ JACOBI_ASGN_SU_BIT1 (a_size, b)); |

77 | } |

78 | |

79 | if (b == 1) |

80 | return JACOBI_BIT1_TO_PN (result_bit1); /* (a/1)=1 for any a */ |

81 | |

82 | a_size = ABS(a_size); |

83 | |

84 | /* (a/b) = (a mod b / b) */ |

85 | JACOBI_MOD_OR_MODEXACT_1_ODD (result_bit1, a_rem, a_ptr, a_size, b); |

86 | return mpn_jacobi_base (a_rem, (mp_limb_t) b, result_bit1); |

87 | } |

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