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/* mpn_sub_n -- Subtract two limb vectors of equal, non-zero length.
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"
mp_limb_t
#if __STDC__
mpn_sub_n (mp_ptr res_ptr, mp_srcptr s1_ptr, mp_srcptr s2_ptr, mp_size_t size)
#else
mpn_sub_n (res_ptr, s1_ptr, s2_ptr, size)
register mp_ptr res_ptr;
register mp_srcptr s1_ptr;
register mp_srcptr s2_ptr;
mp_size_t size;
#endif
{
register mp_limb_t x, y, cy;
register mp_size_t j;
/* The loop counter and index J goes from -SIZE to -1. This way
the loop becomes faster. */
j = -size;
/* Offset the base pointers to compensate for the negative indices. */
s1_ptr -= j;
s2_ptr -= j;
res_ptr -= j;
cy = 0;
do
{
y = s2_ptr[j];
x = s1_ptr[j];
y += cy; /* add previous carry to subtrahend */
cy = (y < cy); /* get out carry from that addition */
y = x - y; /* main subtract */
cy = (y > x) + cy; /* get out carry from the subtract, combine */
res_ptr[j] = y;
}
while (++j != 0);
return cy;
}
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