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6b628d36 | 1 | /* mpn_submul_1 -- multiply the S1_SIZE long limb vector pointed to by S1_PTR |
28f540f4 RM |
2 | by S2_LIMB, subtract the S1_SIZE least significant limbs of the product |
3 | from the limb vector pointed to by RES_PTR. Return the most significant | |
4 | limb of the product, adjusted for carry-out from the subtraction. | |
5 | ||
2b778ceb | 6 | Copyright (C) 1992-2021 Free Software Foundation, Inc. |
28f540f4 RM |
7 | |
8 | This file is part of the GNU MP Library. | |
9 | ||
10 | The GNU MP Library is free software; you can redistribute it and/or modify | |
6d84f89a AJ |
11 | it under the terms of the GNU Lesser General Public License as published by |
12 | the Free Software Foundation; either version 2.1 of the License, or (at your | |
28f540f4 RM |
13 | option) any later version. |
14 | ||
15 | The GNU MP Library is distributed in the hope that it will be useful, but | |
16 | WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY | |
6d84f89a | 17 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public |
28f540f4 RM |
18 | License for more details. |
19 | ||
6d84f89a | 20 | You should have received a copy of the GNU Lesser General Public License |
59ba27a6 | 21 | along with the GNU MP Library; see the file COPYING.LIB. If not, see |
5a82c748 | 22 | <https://www.gnu.org/licenses/>. */ |
28f540f4 | 23 | |
9d13fb24 | 24 | #include <gmp.h> |
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25 | #include "gmp-impl.h" |
26 | #include "longlong.h" | |
27 | ||
b928942e | 28 | mp_limb_t |
f63f2bfd JM |
29 | mpn_submul_1 (register mp_ptr res_ptr, register mp_srcptr s1_ptr, |
30 | mp_size_t s1_size, register mp_limb_t s2_limb) | |
28f540f4 | 31 | { |
b928942e | 32 | register mp_limb_t cy_limb; |
28f540f4 | 33 | register mp_size_t j; |
b928942e RM |
34 | register mp_limb_t prod_high, prod_low; |
35 | register mp_limb_t x; | |
28f540f4 RM |
36 | |
37 | /* The loop counter and index J goes from -SIZE to -1. This way | |
38 | the loop becomes faster. */ | |
39 | j = -s1_size; | |
40 | ||
41 | /* Offset the base pointers to compensate for the negative indices. */ | |
42 | res_ptr -= j; | |
43 | s1_ptr -= j; | |
44 | ||
45 | cy_limb = 0; | |
46 | do | |
47 | { | |
48 | umul_ppmm (prod_high, prod_low, s1_ptr[j], s2_limb); | |
49 | ||
50 | prod_low += cy_limb; | |
51 | cy_limb = (prod_low < cy_limb) + prod_high; | |
52 | ||
53 | x = res_ptr[j]; | |
54 | prod_low = x - prod_low; | |
55 | cy_limb += (prod_low > x); | |
56 | res_ptr[j] = prod_low; | |
57 | } | |
58 | while (++j != 0); | |
59 | ||
60 | return cy_limb; | |
61 | } |