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/* mpz_sub_ui -- Subtract an unsigned one-word integer from an MP_INT.
Copyright (C) 1991 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 General Public License as published by
the Free Software Foundation; either version 2, 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with the GNU MP Library; see the file COPYING. If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
#include "gmp.h"
#include "gmp-impl.h"
void
#ifdef __STDC__
mpz_sub_ui (MP_INT *dif, const MP_INT *min, mp_limb sub)
#else
mpz_sub_ui (dif, min, sub)
MP_INT *dif;
const MP_INT *min;
mp_limb sub;
#endif
{
mp_srcptr minp;
mp_ptr difp;
mp_size minsize, difsize;
mp_size abs_minsize;
minsize = min->size;
abs_minsize = ABS (minsize);
/* If not space for SUM (and possible carry), increase space. */
difsize = abs_minsize + 1;
if (dif->alloc < difsize)
_mpz_realloc (dif, difsize);
/* These must be after realloc (ADD1 may be the same as SUM). */
minp = min->d;
difp = dif->d;
if (sub == 0)
{
MPN_COPY (difp, minp, abs_minsize);
dif->size = minsize;
return;
}
if (abs_minsize == 0)
{
difp[0] = sub;
dif->size = -1;
return;
}
if (minsize < 0)
{
difsize = mpn_add (difp, minp, abs_minsize, &sub, 1);
if (difsize != 0)
difp[abs_minsize] = 1;
difsize = -(difsize + abs_minsize);
}
else
{
/* The signs are different. Need exact comparision to determine
which operand to subtract from which. */
if (abs_minsize == 1 && minp[0] < sub)
difsize = -(abs_minsize
+ mpn_sub (difp, &sub, 1, minp, 1));
else
difsize = (abs_minsize
+ mpn_sub (difp, minp, abs_minsize, &sub, 1));
}
dif->size = difsize;
}
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