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comparison libtommath/bn_mp_div_2.c @ 1692:1051e4eea25a

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Update LibTomMath to 1.2.0 (#84) * update C files * update other files * update headers * update makefiles * remove mp_set/get_double() * use ltm 1.2.0 API * update ltm_desc * use bundled tommath if system-tommath is too old * XMALLOC etc. were changed to MP_MALLOC etc.
author Steffen Jaeckel <s@jaeckel.eu>
date Tue, 26 May 2020 17:36:47 +0200
parents f52919ffd3b1
children
comparison
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1691:2d3745d58843 1692:1051e4eea25a
1 #include "tommath_private.h" 1 #include "tommath_private.h"
2 #ifdef BN_MP_DIV_2_C 2 #ifdef BN_MP_DIV_2_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis 3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
4 * 4 /* SPDX-License-Identifier: Unlicense */
5 * LibTomMath is a library that provides multiple-precision
6 * integer arithmetic as well as number theoretic functionality.
7 *
8 * The library was designed directly after the MPI library by
9 * Michael Fromberger but has been written from scratch with
10 * additional optimizations in place.
11 *
12 * SPDX-License-Identifier: Unlicense
13 */
14 5
15 /* b = a/2 */ 6 /* b = a/2 */
16 int mp_div_2(const mp_int *a, mp_int *b) 7 mp_err mp_div_2(const mp_int *a, mp_int *b)
17 { 8 {
18 int x, res, oldused; 9 int x, oldused;
10 mp_digit r, rr, *tmpa, *tmpb;
11 mp_err err;
19 12
20 /* copy */ 13 /* copy */
21 if (b->alloc < a->used) { 14 if (b->alloc < a->used) {
22 if ((res = mp_grow(b, a->used)) != MP_OKAY) { 15 if ((err = mp_grow(b, a->used)) != MP_OKAY) {
23 return res; 16 return err;
24 } 17 }
25 } 18 }
26 19
27 oldused = b->used; 20 oldused = b->used;
28 b->used = a->used; 21 b->used = a->used;
29 {
30 mp_digit r, rr, *tmpa, *tmpb;
31 22
32 /* source alias */ 23 /* source alias */
33 tmpa = a->dp + b->used - 1; 24 tmpa = a->dp + b->used - 1;
34 25
35 /* dest alias */ 26 /* dest alias */
36 tmpb = b->dp + b->used - 1; 27 tmpb = b->dp + b->used - 1;
37 28
38 /* carry */ 29 /* carry */
39 r = 0; 30 r = 0;
40 for (x = b->used - 1; x >= 0; x--) { 31 for (x = b->used - 1; x >= 0; x--) {
41 /* get the carry for the next iteration */ 32 /* get the carry for the next iteration */
42 rr = *tmpa & 1u; 33 rr = *tmpa & 1u;
43 34
44 /* shift the current digit, add in carry and store */ 35 /* shift the current digit, add in carry and store */
45 *tmpb-- = (*tmpa-- >> 1) | (r << (DIGIT_BIT - 1)); 36 *tmpb-- = (*tmpa-- >> 1) | (r << (MP_DIGIT_BIT - 1));
46 37
47 /* forward carry to next iteration */ 38 /* forward carry to next iteration */
48 r = rr; 39 r = rr;
49 } 40 }
50 41
51 /* zero excess digits */ 42 /* zero excess digits */
52 tmpb = b->dp + b->used; 43 MP_ZERO_DIGITS(b->dp + b->used, oldused - b->used);
53 for (x = b->used; x < oldused; x++) { 44
54 *tmpb++ = 0;
55 }
56 }
57 b->sign = a->sign; 45 b->sign = a->sign;
58 mp_clamp(b); 46 mp_clamp(b);
59 return MP_OKAY; 47 return MP_OKAY;
60 } 48 }
61 #endif 49 #endif
62
63 /* ref: HEAD -> master, tag: v1.1.0 */
64 /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
65 /* commit time: 2019-01-28 20:32:32 +0100 */