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Annotation of OpenXM_contrib/gmp/mpn/generic/sub_n.c, Revision 1.1.1.1

1.1       maekawa     1: /* mpn_sub_n -- Subtract two limb vectors of equal, non-zero length.
                      2:
                      3: Copyright (C) 1992, 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: mp_limb_t
                     26: #if __STDC__
                     27: mpn_sub_n (mp_ptr res_ptr, mp_srcptr s1_ptr, mp_srcptr s2_ptr, mp_size_t size)
                     28: #else
                     29: mpn_sub_n (res_ptr, s1_ptr, s2_ptr, size)
                     30:      register mp_ptr res_ptr;
                     31:      register mp_srcptr s1_ptr;
                     32:      register mp_srcptr s2_ptr;
                     33:      mp_size_t size;
                     34: #endif
                     35: {
                     36:   register mp_limb_t x, y, cy;
                     37:   register mp_size_t j;
                     38:
                     39:   /* The loop counter and index J goes from -SIZE to -1.  This way
                     40:      the loop becomes faster.  */
                     41:   j = -size;
                     42:
                     43:   /* Offset the base pointers to compensate for the negative indices.  */
                     44:   s1_ptr -= j;
                     45:   s2_ptr -= j;
                     46:   res_ptr -= j;
                     47:
                     48:   cy = 0;
                     49:   do
                     50:     {
                     51:       y = s2_ptr[j];
                     52:       x = s1_ptr[j];
                     53:       y += cy;                 /* add previous carry to subtrahend */
                     54:       cy = (y < cy);           /* get out carry from that addition */
                     55:       y = x - y;               /* main subtract */
                     56:       cy = (y > x) + cy;       /* get out carry from the subtract, combine */
                     57:       res_ptr[j] = y;
                     58:     }
                     59:   while (++j != 0);
                     60:
                     61:   return cy;
                     62: }