| Austin Schuh | dace2a6 | 2020-08-18 10:56:48 -0700 | [diff] [blame] | 1 | /* mpz_kronecker_ui -- mpz+ulong Kronecker/Jacobi symbol. |
| 2 | |
| 3 | Copyright 1999-2002 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 either: |
| 9 | |
| 10 | * the GNU Lesser General Public License as published by the Free |
| 11 | Software Foundation; either version 3 of the License, or (at your |
| 12 | option) any later version. |
| 13 | |
| 14 | or |
| 15 | |
| 16 | * the GNU General Public License as published by the Free Software |
| 17 | Foundation; either version 2 of the License, or (at your option) any |
| 18 | later version. |
| 19 | |
| 20 | or both in parallel, as here. |
| 21 | |
| 22 | The GNU MP Library is distributed in the hope that it will be useful, but |
| 23 | WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
| 24 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 25 | for more details. |
| 26 | |
| 27 | You should have received copies of the GNU General Public License and the |
| 28 | GNU Lesser General Public License along with the GNU MP Library. If not, |
| 29 | see https://www.gnu.org/licenses/. */ |
| 30 | |
| 31 | #include "gmp-impl.h" |
| 32 | #include "longlong.h" |
| 33 | |
| 34 | |
| 35 | int |
| 36 | mpz_kronecker_ui (mpz_srcptr a, unsigned long b) |
| 37 | { |
| 38 | mp_srcptr a_ptr; |
| 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 | a_ptr = PTR(a); |
| 58 | if ((b & 1) != 0) |
| 59 | { |
| 60 | result_bit1 = JACOBI_ASGN_SU_BIT1 (a_size, b); |
| 61 | } |
| 62 | else |
| 63 | { |
| 64 | mp_limb_t a_low = a_ptr[0]; |
| 65 | int twos; |
| 66 | |
| 67 | if (b == 0) |
| 68 | return JACOBI_LS0 (a_low, a_size); /* (a/0) */ |
| 69 | |
| 70 | if (! (a_low & 1)) |
| 71 | return 0; /* (even/even)=0 */ |
| 72 | |
| 73 | /* (a/2)=(2/a) for a odd */ |
| 74 | count_trailing_zeros (twos, b); |
| 75 | b >>= twos; |
| 76 | result_bit1 = (JACOBI_TWOS_U_BIT1 (twos, a_low) |
| 77 | ^ JACOBI_ASGN_SU_BIT1 (a_size, b)); |
| 78 | } |
| 79 | |
| 80 | if (b == 1) |
| 81 | return JACOBI_BIT1_TO_PN (result_bit1); /* (a/1)=1 for any a */ |
| 82 | |
| 83 | a_size = ABS(a_size); |
| 84 | |
| 85 | /* (a/b) = (a mod b / b) */ |
| 86 | JACOBI_MOD_OR_MODEXACT_1_ODD (result_bit1, a_rem, a_ptr, a_size, b); |
| 87 | return mpn_jacobi_base (a_rem, (mp_limb_t) b, result_bit1); |
| 88 | } |