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54 lines
1.6 KiB
C
54 lines
1.6 KiB
C
/* mpn_sub_n -- Subtract two limb vectors of equal, non-zero length.
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Copyright (C) 1992-2016 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or (at your
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option) any later version.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MP Library; see the file COPYING.LIB. If not, see
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<http://www.gnu.org/licenses/>. */
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#include <gmp.h>
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#include "gmp-impl.h"
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mp_limb_t
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mpn_sub_n (mp_ptr res_ptr, mp_srcptr s1_ptr, mp_srcptr s2_ptr, mp_size_t size)
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{
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register mp_limb_t x, y, cy;
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register mp_size_t j;
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/* The loop counter and index J goes from -SIZE to -1. This way
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the loop becomes faster. */
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j = -size;
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/* Offset the base pointers to compensate for the negative indices. */
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s1_ptr -= j;
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s2_ptr -= j;
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res_ptr -= j;
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cy = 0;
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do
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{
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y = s2_ptr[j];
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x = s1_ptr[j];
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y += cy; /* add previous carry to subtrahend */
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cy = (y < cy); /* get out carry from that addition */
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y = x - y; /* main subtract */
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cy = (y > x) + cy; /* get out carry from the subtract, combine */
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res_ptr[j] = y;
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}
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while (++j != 0);
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return cy;
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}
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