1/* mpn_sub_n -- Subtract two limb vectors of equal, non-zero length.
2
3Copyright (C) 1992, 1993, 1994, 1996 Free Software Foundation, Inc.
4
5This file is part of the GNU MP Library.
6
7The GNU MP Library is free software; you can redistribute it and/or modify
8it under the terms of the GNU Lesser General Public License as published by
9the Free Software Foundation; either version 2.1 of the License, or (at your
10option) any later version.
11
12The GNU MP Library is distributed in the hope that it will be useful, but
13WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
14or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
15License for more details.
16
17You should have received a copy of the GNU Lesser General Public License
18along with the GNU MP Library; see the file COPYING.LIB. If not, write to
19the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
20MA 02111-1307, USA. */
21
22#include <config.h>
23#include "gmp-impl.h"
24
25mp_limb_t
26#if __STDC__
27mpn_sub_n (mp_ptr res_ptr, mp_srcptr s1_ptr, mp_srcptr s2_ptr, mp_size_t size)
28#else
29mpn_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}
63