1 | /* mpn_sub_n -- Subtract two limb vectors of equal, non-zero length. |
2 | |
3 | Copyright (C) 1992-2022 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 Lesser General Public License as published by |
9 | the Free Software Foundation; either version 2.1 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 Lesser General Public |
15 | License for more details. |
16 | |
17 | You should have received a copy of the GNU Lesser General Public License |
18 | along with the GNU MP Library; see the file COPYING.LIB. If not, see |
19 | <https://www.gnu.org/licenses/>. */ |
20 | |
21 | #include <gmp.h> |
22 | #include "gmp-impl.h" |
23 | |
24 | mp_limb_t |
25 | mpn_sub_n (mp_ptr res_ptr, mp_srcptr s1_ptr, mp_srcptr s2_ptr, mp_size_t size) |
26 | { |
27 | register mp_limb_t x, y, cy; |
28 | register mp_size_t j; |
29 | |
30 | /* The loop counter and index J goes from -SIZE to -1. This way |
31 | the loop becomes faster. */ |
32 | j = -size; |
33 | |
34 | /* Offset the base pointers to compensate for the negative indices. */ |
35 | s1_ptr -= j; |
36 | s2_ptr -= j; |
37 | res_ptr -= j; |
38 | |
39 | cy = 0; |
40 | do |
41 | { |
42 | y = s2_ptr[j]; |
43 | x = s1_ptr[j]; |
44 | y += cy; /* add previous carry to subtrahend */ |
45 | cy = (y < cy); /* get out carry from that addition */ |
46 | y = x - y; /* main subtract */ |
47 | cy = (y > x) + cy; /* get out carry from the subtract, combine */ |
48 | res_ptr[j] = y; |
49 | } |
50 | while (++j != 0); |
51 | |
52 | return cy; |
53 | } |
54 | |