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6b628d36 | 1 | /* mpn_sub_n -- Subtract two limb vectors of equal, non-zero length. |
28f540f4 | 2 | |
d4697bc9 | 3 | Copyright (C) 1992-2014 Free Software Foundation, Inc. |
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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 | |
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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 | |
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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 | |
6d84f89a | 14 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public |
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15 | License for more details. |
16 | ||
6d84f89a | 17 | You should have received a copy of the GNU Lesser General Public License |
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18 | along with the GNU MP Library; see the file COPYING.LIB. If not, see |
19 | <http://www.gnu.org/licenses/>. */ | |
28f540f4 | 20 | |
9d13fb24 | 21 | #include <gmp.h> |
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22 | #include "gmp-impl.h" |
23 | ||
b928942e | 24 | mp_limb_t |
28f540f4 | 25 | #if __STDC__ |
6b628d36 | 26 | mpn_sub_n (mp_ptr res_ptr, mp_srcptr s1_ptr, mp_srcptr s2_ptr, mp_size_t size) |
28f540f4 | 27 | #else |
6b628d36 | 28 | mpn_sub_n (res_ptr, s1_ptr, s2_ptr, size) |
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29 | register mp_ptr res_ptr; |
30 | register mp_srcptr s1_ptr; | |
31 | register mp_srcptr s2_ptr; | |
32 | mp_size_t size; | |
33 | #endif | |
34 | { | |
b928942e | 35 | register mp_limb_t x, y, cy; |
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36 | register mp_size_t j; |
37 | ||
38 | /* The loop counter and index J goes from -SIZE to -1. This way | |
39 | the loop becomes faster. */ | |
40 | j = -size; | |
41 | ||
42 | /* Offset the base pointers to compensate for the negative indices. */ | |
43 | s1_ptr -= j; | |
44 | s2_ptr -= j; | |
45 | res_ptr -= j; | |
46 | ||
47 | cy = 0; | |
48 | do | |
49 | { | |
50 | y = s2_ptr[j]; | |
51 | x = s1_ptr[j]; | |
52 | y += cy; /* add previous carry to subtrahend */ | |
53 | cy = (y < cy); /* get out carry from that addition */ | |
54 | y = x - y; /* main subtract */ | |
55 | cy = (y > x) + cy; /* get out carry from the subtract, combine */ | |
56 | res_ptr[j] = y; | |
57 | } | |
58 | while (++j != 0); | |
59 | ||
60 | return cy; | |
61 | } |