Mercurial > dropbear

comparison libtommath/bn_s_mp_sub.c @ 1692:1051e4eea25a

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
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
equal deleted inserted replaced
1691:2d3745d58843 1692:1051e4eea25a
1 #include "tommath_private.h" 1 #include "tommath_private.h"
2 #ifdef BN_S_MP_SUB_C 2 #ifdef BN_S_MP_SUB_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 /* low level subtraction (assumes |a| > |b|), HAC pp.595 Algorithm 14.9 */ 6 /* low level subtraction (assumes |a| > |b|), HAC pp.595 Algorithm 14.9 */
16 int s_mp_sub(const mp_int *a, const mp_int *b, mp_int *c) 7 mp_err s_mp_sub(const mp_int *a, const mp_int *b, mp_int *c)
17 { 8 {
18 int olduse, res, min, max; 9 int olduse, min, max;
10 mp_err err;
19 11
20 /* find sizes */ 12 /* find sizes */
21 min = b->used; 13 min = b->used;
22 max = a->used; 14 max = a->used;
23 15
24 /* init result */ 16 /* init result */
25 if (c->alloc < max) { 17 if (c->alloc < max) {
26 if ((res = mp_grow(c, max)) != MP_OKAY) { 18 if ((err = mp_grow(c, max)) != MP_OKAY) {
27 return res; 19 return err;
28 } 20 }
29 } 21 }
30 olduse = c->used; 22 olduse = c->used;
31 c->used = max; 23 c->used = max;
32 24
48 /* U = carry bit of T[i] 40 /* U = carry bit of T[i]
49 * Note this saves performing an AND operation since 41 * Note this saves performing an AND operation since
50 * if a carry does occur it will propagate all the way to the 42 * if a carry does occur it will propagate all the way to the
51 * MSB. As a result a single shift is enough to get the carry 43 * MSB. As a result a single shift is enough to get the carry
52 */ 44 */
53 u = *tmpc >> (((size_t)CHAR_BIT * sizeof(mp_digit)) - 1u); 45 u = *tmpc >> (MP_SIZEOF_BITS(mp_digit) - 1u);
54 46
55 /* Clear carry from T[i] */ 47 /* Clear carry from T[i] */
56 *tmpc++ &= MP_MASK; 48 *tmpc++ &= MP_MASK;
57 } 49 }
58 50
60 for (; i < max; i++) { 52 for (; i < max; i++) {
61 /* T[i] = A[i] - U */ 53 /* T[i] = A[i] - U */
62 *tmpc = *tmpa++ - u; 54 *tmpc = *tmpa++ - u;
63 55
64 /* U = carry bit of T[i] */ 56 /* U = carry bit of T[i] */
65 u = *tmpc >> (((size_t)CHAR_BIT * sizeof(mp_digit)) - 1u); 57 u = *tmpc >> (MP_SIZEOF_BITS(mp_digit) - 1u);
66 58
67 /* Clear carry from T[i] */ 59 /* Clear carry from T[i] */
68 *tmpc++ &= MP_MASK; 60 *tmpc++ &= MP_MASK;
69 } 61 }
70 62
71 /* clear digits above used (since we may not have grown result above) */ 63 /* clear digits above used (since we may not have grown result above) */
72 for (i = c->used; i < olduse; i++) { 64 MP_ZERO_DIGITS(tmpc, olduse - c->used);
73 *tmpc++ = 0;
74 }
75 } 65 }
76 66
77 mp_clamp(c); 67 mp_clamp(c);
78 return MP_OKAY; 68 return MP_OKAY;
79 } 69 }
80 70
81 #endif 71 #endif
82
83 /* ref: HEAD -> master, tag: v1.1.0 */
84 /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
85 /* commit time: 2019-01-28 20:32:32 +0100 */