113 lines
2.9 KiB
C
113 lines
2.9 KiB
C
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/*=============================================================================
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This file is part of FLINT.
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FLINT is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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FLINT is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with FLINT; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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=============================================================================*/
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/******************************************************************************
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Copyright (C) 2008 Peter Shrimpton
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Copyright (C) 2009 William Hart
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******************************************************************************/
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#include <gmp.h>
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#include "flint.h"
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#include "ulong_extras.h"
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int
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n_jacobi_unsigned(mp_limb_t x, mp_limb_t y)
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{
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mp_limb_t a, b, temp;
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int s, exp;
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a = x;
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b = y;
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s = 1;
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if ((a < b) && (b != UWORD(1)))
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{
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if (a == UWORD(0))
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return 0;
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temp = a;
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a = b;
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b = temp;
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count_trailing_zeros(exp, b);
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b >>= exp;
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/* We are only interested in values mod 8, so overflows don't matter here */
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if (((exp * (a * a - 1)) / 8) % 2 == UWORD(1))
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s = -s;
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/* We are only interested in values mod 4, so overflows don't matter here */
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if ((((a - 1) * (b - 1)) / 4) % 2 == UWORD(1))
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s = -s;
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}
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while (b != UWORD(1))
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{
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if ((a >> 2) < b)
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{
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temp = a - b;
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a = b;
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if (temp < b)
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b = temp;
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else if (temp < (b << 1))
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b = temp - a;
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else
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b = temp - (a << 1);
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}
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else
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{
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temp = a % b;
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a = b;
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b = temp;
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}
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if (b == UWORD(0))
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return 0;
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count_trailing_zeros(exp, b);
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b >>= exp;
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/* We are only interested in values mod 8, so overflows don't matter here */
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if (((exp * (a * a - 1)) / 8) % 2 == UWORD(1))
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s = -s;
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/* We are only interested in values mod 4, so overflows don't matter here */
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if ((((a - 1) * (b - 1)) / 4) % 2 == UWORD(1))
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s = -s;
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}
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return s;
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}
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int
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n_jacobi(mp_limb_signed_t x, mp_limb_t y)
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{
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if (x < WORD(0))
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{
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if (((y - 1) / 2) % 2 == UWORD(1))
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return -n_jacobi_unsigned(-x, y);
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else
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return n_jacobi_unsigned(-x, y);
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}
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else
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return n_jacobi_unsigned(x, y);
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}
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