85 lines
2.2 KiB
C
85 lines
2.2 KiB
C
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/* mpz_sub_ui -- Subtract an unsigned one-word integer from an MP_INT.
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Copyright (C) 1991 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 General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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The GNU MP Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with the GNU MP Library; see the file COPYING. If not, write to
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the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
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#include "gmp.h"
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#include "gmp-impl.h"
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void
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#ifdef __STDC__
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mpz_sub_ui (MP_INT *dif, const MP_INT *min, mp_limb sub)
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#else
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mpz_sub_ui (dif, min, sub)
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MP_INT *dif;
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const MP_INT *min;
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mp_limb sub;
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#endif
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{
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mp_srcptr minp;
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mp_ptr difp;
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mp_size minsize, difsize;
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mp_size abs_minsize;
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minsize = min->size;
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abs_minsize = ABS (minsize);
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/* If not space for SUM (and possible carry), increase space. */
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difsize = abs_minsize + 1;
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if (dif->alloc < difsize)
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_mpz_realloc (dif, difsize);
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/* These must be after realloc (ADD1 may be the same as SUM). */
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minp = min->d;
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difp = dif->d;
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if (sub == 0)
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{
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MPN_COPY (difp, minp, abs_minsize);
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dif->size = minsize;
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return;
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}
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if (abs_minsize == 0)
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{
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difp[0] = sub;
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dif->size = -1;
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return;
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}
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if (minsize < 0)
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{
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difsize = mpn_add (difp, minp, abs_minsize, &sub, 1);
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if (difsize != 0)
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difp[abs_minsize] = 1;
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difsize = -(difsize + abs_minsize);
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}
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else
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{
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/* The signs are different. Need exact comparision to determine
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which operand to subtract from which. */
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if (abs_minsize == 1 && minp[0] < sub)
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difsize = -(abs_minsize
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+ mpn_sub (difp, &sub, 1, minp, 1));
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else
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difsize = (abs_minsize
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+ mpn_sub (difp, minp, abs_minsize, &sub, 1));
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}
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dif->size = difsize;
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}
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