92 lines
2.4 KiB
C
92 lines
2.4 KiB
C
/*=============================================================================
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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) 2012 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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#include "fmpz.h"
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void fmpz_xgcd(fmpz_t d, fmpz_t a, fmpz_t b, const fmpz_t f, const fmpz_t g)
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{
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fmpz_t t1, t2;
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fmpz * f1, * g1;
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if (fmpz_is_zero(f))
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{
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fmpz_set(d, g);
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fmpz_set_ui(a, 0);
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fmpz_set_ui(b, 1);
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} else if (fmpz_cmp(f, g) == 0)
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{
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fmpz_set(d, f);
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fmpz_set_ui(a, 1);
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fmpz_set_si(b, 0);
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} else
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{
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int sign1 = fmpz_sgn(f);
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int sign2 = fmpz_sgn(g);
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fmpz_init(t1);
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fmpz_init(t2);
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/* support aliasing */
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if (d == f || a == f || sign1 < 0)
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{
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f1 = t1;
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if (sign1 < 0) fmpz_neg(f1, f);
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else fmpz_set(f1, f);
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} else
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f1 = (fmpz *) f;
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if (d == g || a == g || sign2 < 0)
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{
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g1 = t2;
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if (sign2 < 0) fmpz_neg(g1, g);
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else fmpz_set(g1, g);
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} else
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g1 = (fmpz *) g;
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if (fmpz_cmp(f1, g1) < 0)
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{
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fmpz_gcdinv(d, a, f1, g1);
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fmpz_mul(t1, a, f1);
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fmpz_sub(t1, d, t1);
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fmpz_divexact(b, t1, g1);
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} else /* g < f */
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{
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fmpz_gcdinv(d, b, g1, f1);
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fmpz_mul(t2, b, g1);
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fmpz_sub(t2, d, t2);
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fmpz_divexact(a, t2, f1);
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}
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if (sign1 < 0) fmpz_neg(a, a);
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if (sign2 < 0) fmpz_neg(b, b);
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fmpz_clear(t1);
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fmpz_clear(t2);
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}
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}
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