118 lines
3.0 KiB
C
118 lines
3.0 KiB
C
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/* mpz_sub -- Subtract two integers.
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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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#ifndef BERKELEY_MP
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void
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#ifdef __STDC__
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mpz_sub (MP_INT *w, const MP_INT *u, const MP_INT *v)
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#else
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mpz_sub (w, u, v)
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MP_INT *w;
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const MP_INT *u;
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const MP_INT *v;
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#endif
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#else /* BERKELEY_MP */
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void
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#ifdef __STDC__
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msub (const MP_INT *u, const MP_INT *v, MP_INT *w)
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#else
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msub (u, v, w)
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const MP_INT *u;
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const MP_INT *v;
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MP_INT *w;
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#endif
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#endif /* BERKELEY_MP */
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{
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mp_srcptr up, vp;
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mp_ptr wp;
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mp_size usize, vsize, wsize;
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mp_size abs_usize;
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mp_size abs_vsize;
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usize = u->size;
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vsize = -v->size; /* The "-" makes the difference from mpz_add */
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abs_usize = ABS (usize);
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abs_vsize = ABS (vsize);
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if (abs_usize < abs_vsize)
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{
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/* Swap U and V. */
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{const MP_INT *t = u; u = v; v = t;}
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{mp_size t = usize; usize = vsize; vsize = t;}
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{mp_size t = abs_usize; abs_usize = abs_vsize; abs_vsize = t;}
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}
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/* True: abs(USIZE) >= abs(VSIZE) */
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/* If not space for sum (and possible carry), increase space. */
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wsize = abs_usize + 1;
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if (w->alloc < wsize)
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_mpz_realloc (w, wsize);
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/* These must be after realloc (u or v may be the same as w). */
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up = u->d;
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vp = v->d;
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wp = w->d;
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if (usize >= 0)
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{
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if (vsize >= 0)
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{
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wsize = mpn_add (wp, up, abs_usize, vp, abs_vsize);
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if (wsize != 0)
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wp[abs_usize] = 1;
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wsize = wsize + abs_usize;
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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_usize == abs_vsize && mpn_cmp (up, vp, abs_usize) < 0)
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wsize = -(abs_usize + mpn_sub (wp, vp, abs_usize, up, abs_usize));
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else
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wsize = abs_usize + mpn_sub (wp, up, abs_usize, vp, abs_vsize);
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}
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}
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else
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{
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if (vsize >= 0)
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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_usize == abs_vsize && mpn_cmp (up, vp, abs_usize) < 0)
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wsize = abs_usize + mpn_sub (wp, vp, abs_usize, up, abs_usize);
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else
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wsize = -(abs_usize + mpn_sub (wp, up, abs_usize, vp, abs_vsize));
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}
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else
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{
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wsize = mpn_add (wp, up, abs_usize, vp, abs_vsize);
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if (wsize != 0)
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wp[abs_usize] = 1;
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wsize = -(wsize + abs_usize);
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}
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}
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w->size = wsize;
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}
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