Mercurial > dropbear

comparison libtommath/bn_mp_sub_d.c @ 1436:60fc6476e044

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Update to libtommath v1.0
author Matt Johnston <matt@ucc.asn.au>
date Sat, 24 Jun 2017 22:37:14 +0800
parents 5ff8218bcee9
children 8bba51a55704
comparison
equal deleted inserted replaced
1435:f849a5ca2efc 1436:60fc6476e044
1 #include <tommath.h> 1 #include <tommath_private.h>
2 #ifdef BN_MP_SUB_D_C 2 #ifdef BN_MP_SUB_D_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis 3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
4 * 4 *
5 * LibTomMath is a library that provides multiple-precision 5 * LibTomMath is a library that provides multiple-precision
6 * integer arithmetic as well as number theoretic functionality. 6 * integer arithmetic as well as number theoretic functionality.
10 * additional optimizations in place. 10 * additional optimizations in place.
11 * 11 *
12 * The library is free for all purposes without any express 12 * The library is free for all purposes without any express
13 * guarantee it works. 13 * guarantee it works.
14 * 14 *
15 * Tom St Denis, [email protected], http://math.libtomcrypt.com 15 * Tom St Denis, [email protected], http://libtom.org
16 */ 16 */
17 17
18 /* single digit subtraction */ 18 /* single digit subtraction */
19 int 19 int
20 mp_sub_d (mp_int * a, mp_digit b, mp_int * c) 20 mp_sub_d (mp_int * a, mp_digit b, mp_int * c)
21 { 21 {
22 mp_digit *tmpa, *tmpc, mu; 22 mp_digit *tmpa, *tmpc, mu;
23 int res, ix, oldused; 23 int res, ix, oldused;
24 24
25 /* grow c as required */ 25 /* grow c as required */
26 if (c->alloc < a->used + 1) { 26 if (c->alloc < (a->used + 1)) {
27 if ((res = mp_grow(c, a->used + 1)) != MP_OKAY) { 27 if ((res = mp_grow(c, a->used + 1)) != MP_OKAY) {
28 return res; 28 return res;
29 } 29 }
30 } 30 }
31 31
47 oldused = c->used; 47 oldused = c->used;
48 tmpa = a->dp; 48 tmpa = a->dp;
49 tmpc = c->dp; 49 tmpc = c->dp;
50 50
51 /* if a <= b simply fix the single digit */ 51 /* if a <= b simply fix the single digit */
52 if ((a->used == 1 && a->dp[0] <= b) || a->used == 0) { 52 if (((a->used == 1) && (a->dp[0] <= b)) || (a->used == 0)) {
53 if (a->used == 1) { 53 if (a->used == 1) {
54 *tmpc++ = b - *tmpa; 54 *tmpc++ = b - *tmpa;
55 } else { 55 } else {
56 *tmpc++ = b; 56 *tmpc++ = b;
57 } 57 }
65 c->sign = MP_ZPOS; 65 c->sign = MP_ZPOS;
66 c->used = a->used; 66 c->used = a->used;
67 67
68 /* subtract first digit */ 68 /* subtract first digit */
69 *tmpc = *tmpa++ - b; 69 *tmpc = *tmpa++ - b;
70 mu = *tmpc >> (sizeof(mp_digit) * CHAR_BIT - 1); 70 mu = *tmpc >> ((sizeof(mp_digit) * CHAR_BIT) - 1);
71 *tmpc++ &= MP_MASK; 71 *tmpc++ &= MP_MASK;
72 72
73 /* handle rest of the digits */ 73 /* handle rest of the digits */
74 for (ix = 1; ix < a->used; ix++) { 74 for (ix = 1; ix < a->used; ix++) {
75 *tmpc = *tmpa++ - mu; 75 *tmpc = *tmpa++ - mu;
76 mu = *tmpc >> (sizeof(mp_digit) * CHAR_BIT - 1); 76 mu = *tmpc >> ((sizeof(mp_digit) * CHAR_BIT) - 1);
77 *tmpc++ &= MP_MASK; 77 *tmpc++ &= MP_MASK;
78 } 78 }
79 } 79 }
80 80
81 /* zero excess digits */ 81 /* zero excess digits */
86 return MP_OKAY; 86 return MP_OKAY;
87 } 87 }
88 88
89 #endif 89 #endif
90 90
91 /* $Source: /cvs/libtom/libtommath/bn_mp_sub_d.c,v $ */ 91 /* $Source$ */
92 /* $Revision: 1.5 $ */ 92 /* $Revision$ */
93 /* $Date: 2006/03/31 14:18:44 $ */ 93 /* $Date$ */