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Annotation of OpenXM_contrib/gmp/mpz/sub_ui.c, Revision 1.1.1.1

1.1       maekawa     1: /* mpz_sub_ui -- Subtract an unsigned one-word integer from an MP_INT.
                      2:
                      3: Copyright (C) 1991, 1993, 1994, 1996 Free Software Foundation, Inc.
                      4:
                      5: This file is part of the GNU MP Library.
                      6:
                      7: The GNU MP Library is free software; you can redistribute it and/or modify
                      8: it under the terms of the GNU Library General Public License as published by
                      9: the Free Software Foundation; either version 2 of the License, or (at your
                     10: option) any later version.
                     11:
                     12: The GNU MP Library is distributed in the hope that it will be useful, but
                     13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
                     14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
                     15: License for more details.
                     16:
                     17: You should have received a copy of the GNU Library General Public License
                     18: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
                     19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
                     20: MA 02111-1307, USA. */
                     21:
                     22: #include "gmp.h"
                     23: #include "gmp-impl.h"
                     24:
                     25: void
                     26: #if __STDC__
                     27: mpz_sub_ui (mpz_ptr w, mpz_srcptr u, unsigned long int v)
                     28: #else
                     29: mpz_sub_ui (w, u, v)
                     30:      mpz_ptr w;
                     31:      mpz_srcptr u;
                     32:      unsigned long int v;
                     33: #endif
                     34: {
                     35:   mp_srcptr up;
                     36:   mp_ptr wp;
                     37:   mp_size_t usize, wsize;
                     38:   mp_size_t abs_usize;
                     39:
                     40:   usize = u->_mp_size;
                     41:   abs_usize = ABS (usize);
                     42:
                     43:   /* If not space for W (and possible carry), increase space.  */
                     44:   wsize = abs_usize + 1;
                     45:   if (w->_mp_alloc < wsize)
                     46:     _mpz_realloc (w, wsize);
                     47:
                     48:   /* These must be after realloc (U may be the same as W).  */
                     49:   up = u->_mp_d;
                     50:   wp = w->_mp_d;
                     51:
                     52:   if (abs_usize == 0)
                     53:     {
                     54:       wp[0] = v;
                     55:       w->_mp_size = -(v != 0);
                     56:       return;
                     57:     }
                     58:
                     59:   if (usize < 0)
                     60:     {
                     61:       mp_limb_t cy;
                     62:       cy = mpn_add_1 (wp, up, abs_usize, v);
                     63:       wp[abs_usize] = cy;
                     64:       wsize = -(abs_usize + cy);
                     65:     }
                     66:   else
                     67:     {
                     68:       /* The signs are different.  Need exact comparison to determine
                     69:         which operand to subtract from which.  */
                     70:       if (abs_usize == 1 && up[0] < v)
                     71:        {
                     72:          wp[0] = v - up[0];
                     73:          wsize = -1;
                     74:        }
                     75:       else
                     76:        {
                     77:          mpn_sub_1 (wp, up, abs_usize, v);
                     78:          /* Size can decrease with at most one limb.  */
                     79:          wsize = abs_usize - (wp[abs_usize - 1] == 0);
                     80:        }
                     81:     }
                     82:
                     83:   w->_mp_size = wsize;
                     84: }