blob: bc0691a0d14f7deddcc75b0ab8a847ca6eef6bdc (
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
|
#include "tommath_private.h"
#ifdef BN_MP_MUL_2_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
/* b = a*2 */
mp_err mp_mul_2(const mp_int *a, mp_int *b)
{
int x, oldused;
mp_err err;
/* grow to accomodate result */
if (b->alloc < (a->used + 1)) {
if ((err = mp_grow(b, a->used + 1)) != MP_OKAY) {
return err;
}
}
oldused = b->used;
b->used = a->used;
{
mp_digit r, rr, *tmpa, *tmpb;
/* alias for source */
tmpa = a->dp;
/* alias for dest */
tmpb = b->dp;
/* carry */
r = 0;
for (x = 0; x < a->used; x++) {
/* get what will be the *next* carry bit from the
* MSB of the current digit
*/
rr = *tmpa >> (mp_digit)(MP_DIGIT_BIT - 1);
/* now shift up this digit, add in the carry [from the previous] */
*tmpb++ = ((*tmpa++ << 1uL) | r) & MP_MASK;
/* copy the carry that would be from the source
* digit into the next iteration
*/
r = rr;
}
/* new leading digit? */
if (r != 0u) {
/* add a MSB which is always 1 at this point */
*tmpb = 1;
++(b->used);
}
/* now zero any excess digits on the destination
* that we didn't write to
*/
MP_ZERO_DIGITS(b->dp + b->used, oldused - b->used);
}
b->sign = a->sign;
return MP_OKAY;
}
#endif
|
