79 lines
2.7 KiB
C
79 lines
2.7 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) 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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#include "fmpz.h"
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void
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fmpz_sub(fmpz_t f, const fmpz_t g, const fmpz_t h)
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{
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fmpz c1 = *g;
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fmpz c2 = *h;
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if (!COEFF_IS_MPZ(c1)) /* g is small */
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{
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if (!COEFF_IS_MPZ(c2)) /* both inputs are small */
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{
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fmpz_set_si(f, c1 - c2);
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}
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else /* g is small, h is large */
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{
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__mpz_struct *mpz3 = _fmpz_promote(f); /* g is saved and h is large */
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__mpz_struct *mpz2 = COEFF_TO_PTR(c2);
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if (c1 < WORD(0))
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{
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flint_mpz_add_ui(mpz3, mpz2, -c1);
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mpz_neg(mpz3, mpz3);
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}
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else
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flint_mpz_ui_sub(mpz3, c1, mpz2);
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_fmpz_demote_val(f); /* may have cancelled */
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}
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}
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else
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{
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if (!COEFF_IS_MPZ(c2)) /* g is large, h is small */
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{
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__mpz_struct *mpz3 = _fmpz_promote(f); /* h is saved and g is large */
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__mpz_struct *mpz1 = COEFF_TO_PTR(c1);
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if (c2 < WORD(0))
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flint_mpz_add_ui(mpz3, mpz1, -c2);
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else
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flint_mpz_sub_ui(mpz3, mpz1, c2);
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_fmpz_demote_val(f); /* may have cancelled */
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}
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else /* g and h are large */
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{
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__mpz_struct *mpz3 = _fmpz_promote(f); /* aliasing means f is already large */
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__mpz_struct *mpz1 = COEFF_TO_PTR(c1);
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__mpz_struct *mpz2 = COEFF_TO_PTR(c2);
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mpz_sub(mpz3, mpz1, mpz2);
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_fmpz_demote_val(f); /* may have cancelled */
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}
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}
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}
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