61 lines
2.1 KiB
C
61 lines
2.1 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_ui(fmpz_t f, const fmpz_t g, ulong x)
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{
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fmpz c = *g;
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if (!COEFF_IS_MPZ(c)) /* coeff is small */
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{
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mp_limb_t sum[2];
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if (c < WORD(0)) /* g negative, x positive, so difference is negative */
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{
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add_ssaaaa(sum[1], sum[0], 0, -c, 0, x);
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fmpz_neg_uiui(f, sum[1], sum[0]);
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}
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else /* coeff is non-negative, x non-negative */
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{
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if (x < c)
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fmpz_set_ui(f, c - x); /* won't be negative and is smaller than c */
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else
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fmpz_neg_ui(f, x - c); /* positive or zero */
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}
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}
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else
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{
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__mpz_struct *mpz_ptr, *mpz_ptr2;
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mpz_ptr2 = _fmpz_promote(f); /* g is already large */
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mpz_ptr = COEFF_TO_PTR(c);
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flint_mpz_sub_ui(mpz_ptr2, mpz_ptr, x);
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_fmpz_demote_val(f); /* cancellation may have occurred */
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}
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}
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