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/* mpn_submul_1 -- multiply the S1_SIZE long limb vector pointed to by S1_PTR
by S2_LIMB, subtract the S1_SIZE least significant limbs of the product
from the limb vector pointed to by RES_PTR. Return the most significant
limb of the product, adjusted for carry-out from the subtraction.
Copyright (C) 1992, 1993, 1994, 1996 Free Software Foundation, Inc.
This file is part of the GNU MP Library.
The GNU MP Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Library General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at your
option) any later version.
The GNU MP Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
License for more details.
You should have received a copy of the GNU Library General Public License
along with the GNU MP Library; see the file COPYING.LIB. If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */
#include "gmp.h"
#include "gmp-impl.h"
#include "longlong.h"
mp_limb_t
mpn_submul_1 (res_ptr, s1_ptr, s1_size, s2_limb)
register mp_ptr res_ptr;
register mp_srcptr s1_ptr;
mp_size_t s1_size;
register mp_limb_t s2_limb;
{
register mp_limb_t cy_limb;
register mp_size_t j;
register mp_limb_t prod_high, prod_low;
register mp_limb_t x;
/* The loop counter and index J goes from -SIZE to -1. This way
the loop becomes faster. */
j = -s1_size;
/* Offset the base pointers to compensate for the negative indices. */
res_ptr -= j;
s1_ptr -= j;
cy_limb = 0;
do
{
umul_ppmm (prod_high, prod_low, s1_ptr[j], s2_limb);
prod_low += cy_limb;
cy_limb = (prod_low < cy_limb) + prod_high;
x = res_ptr[j];
prod_low = x - prod_low;
cy_limb += (prod_low > x);
res_ptr[j] = prod_low;
}
while (++j != 0);
return cy_limb;
}
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