66 lines
2.0 KiB
C
66 lines
2.0 KiB
C
/* mpn_submul_1 -- multiply the S1_SIZE long limb vector pointed to by S1_PTR
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by S2_LIMB, subtract the S1_SIZE least significant limbs of the product
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from the limb vector pointed to by RES_PTR. Return the most significant
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limb of the product, adjusted for carry-out from the subtraction.
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Copyright (C) 1992, 1993, 1994, 1996 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, write to
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the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
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MA 02111-1307, USA. */
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#include "gmp.h"
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#include "gmp-impl.h"
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#include "longlong.h"
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mp_limb_t
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mpn_submul_1 (res_ptr, s1_ptr, s1_size, s2_limb)
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register mp_ptr res_ptr;
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register mp_srcptr s1_ptr;
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mp_size_t s1_size;
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register mp_limb_t s2_limb;
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{
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register mp_limb_t cy_limb;
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register mp_size_t j;
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register mp_limb_t prod_high, prod_low;
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register mp_limb_t x;
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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 = -s1_size;
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/* Offset the base pointers to compensate for the negative indices. */
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res_ptr -= j;
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s1_ptr -= j;
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cy_limb = 0;
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do
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{
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umul_ppmm (prod_high, prod_low, s1_ptr[j], s2_limb);
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prod_low += cy_limb;
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cy_limb = (prod_low < cy_limb) + prod_high;
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x = res_ptr[j];
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prod_low = x - prod_low;
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cy_limb += (prod_low > x);
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res_ptr[j] = prod_low;
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}
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while (++j != 0);
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return cy_limb;
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}
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