blob: 3ebf9b48520e27b6e596dc2b25addac3e73e5276 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
|
#include "tommath_private.h"
#ifdef BN_MP_SUB_D_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
/* single digit subtraction */
mp_err mp_sub_d(const mp_int *a, mp_digit b, mp_int *c)
{
mp_digit *tmpa, *tmpc;
mp_err err;
int ix, oldused;
/* grow c as required */
if (c->alloc < (a->used + 1)) {
if ((err = mp_grow(c, a->used + 1)) != MP_OKAY) {
return err;
}
}
/* if a is negative just do an unsigned
* addition [with fudged signs]
*/
if (a->sign == MP_NEG) {
mp_int a_ = *a;
a_.sign = MP_ZPOS;
err = mp_add_d(&a_, b, c);
c->sign = MP_NEG;
/* clamp */
mp_clamp(c);
return err;
}
/* setup regs */
oldused = c->used;
tmpa = a->dp;
tmpc = c->dp;
/* if a <= b simply fix the single digit */
if (((a->used == 1) && (a->dp[0] <= b)) || (a->used == 0)) {
if (a->used == 1) {
*tmpc++ = b - *tmpa;
} else {
*tmpc++ = b;
}
ix = 1;
/* negative/1digit */
c->sign = MP_NEG;
c->used = 1;
} else {
mp_digit mu = b;
/* positive/size */
c->sign = MP_ZPOS;
c->used = a->used;
/* subtract digits, mu is carry */
for (ix = 0; ix < a->used; ix++) {
*tmpc = *tmpa++ - mu;
mu = *tmpc >> (MP_SIZEOF_BITS(mp_digit) - 1u);
*tmpc++ &= MP_MASK;
}
}
/* zero excess digits */
MP_ZERO_DIGITS(tmpc, oldused - ix);
mp_clamp(c);
return MP_OKAY;
}
#endif
|
