kronzs.c
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上传日期:2022-08-06
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- /* mpz_kronecker_si -- mpz+long Kronecker/Jacobi symbol.
- Copyright 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
- This file is part of the GNU MP Library.
- The GNU MP Library is free software; you can redistribute it and/or modify
- it under the terms of the GNU Lesser General Public License as published by
- the Free Software Foundation; either version 3 of the License, or (at your
- option) any later version.
- The GNU MP Library is distributed in the hope that it will be useful, but
- WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
- License for more details.
- You should have received a copy of the GNU Lesser General Public License
- along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
- #include "gmp.h"
- #include "gmp-impl.h"
- #include "longlong.h"
- /* After the absolute value of b is established it's treated as an unsigned
- long, because 0x80..00 doesn't fit in a signed long. */
- int
- mpz_kronecker_si (mpz_srcptr a, long b)
- {
- mp_srcptr a_ptr;
- mp_size_t a_size;
- mp_limb_t a_rem, b_limb;
- int result_bit1;
- a_size = SIZ(a);
- if (a_size == 0)
- return JACOBI_0S (b);
- #if GMP_NUMB_BITS < BITS_PER_ULONG
- if (b > GMP_NUMB_MAX || b < -GMP_NUMB_MAX)
- {
- mp_limb_t blimbs[2];
- mpz_t bz;
- ALLOC(bz) = numberof (blimbs);
- PTR(bz) = blimbs;
- mpz_set_si (bz, b);
- return mpz_kronecker (a, bz);
- }
- #endif
- result_bit1 = JACOBI_BSGN_SS_BIT1 (a_size, b);
- b_limb = (unsigned long) ABS (b);
- a_ptr = PTR(a);
- if ((b_limb & 1) == 0)
- {
- mp_limb_t a_low = a_ptr[0];
- int twos;
- if (b_limb == 0)
- return JACOBI_LS0 (a_low, a_size); /* (a/0) */
- if (! (a_low & 1))
- return 0; /* (even/even)=0 */
- /* (a/2)=(2/a) for a odd */
- count_trailing_zeros (twos, b_limb);
- b_limb >>= twos;
- result_bit1 ^= JACOBI_TWOS_U_BIT1 (twos, a_low);
- }
- if (b_limb == 1)
- return JACOBI_BIT1_TO_PN (result_bit1); /* (a/1)=1 for any a */
- result_bit1 ^= JACOBI_ASGN_SU_BIT1 (a_size, b_limb);
- a_size = ABS(a_size);
- /* (a/b) = (a mod b / b) */
- JACOBI_MOD_OR_MODEXACT_1_ODD (result_bit1, a_rem, a_ptr, a_size, b_limb);
- return mpn_jacobi_base (a_rem, b_limb, result_bit1);
- }