1 #include "tommath_private.h"
2 #ifdef BN_MP_DIV_2_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
4 /* SPDX-License-Identifier: Unlicense */
5
6 /* b = a/2 */
mp_div_2(const mp_int * a,mp_int * b)7 mp_err mp_div_2(const mp_int *a, mp_int *b)
8 {
9 int x, oldused;
10 mp_digit r, rr, *tmpa, *tmpb;
11 mp_err err;
12
13 /* copy */
14 if (b->alloc < a->used) {
15 if ((err = mp_grow(b, a->used)) != MP_OKAY) {
16 return err;
17 }
18 }
19
20 oldused = b->used;
21 b->used = a->used;
22
23 /* source alias */
24 tmpa = a->dp + b->used - 1;
25
26 /* dest alias */
27 tmpb = b->dp + b->used - 1;
28
29 /* carry */
30 r = 0;
31 for (x = b->used - 1; x >= 0; x--) {
32 /* get the carry for the next iteration */
33 rr = *tmpa & 1u;
34
35 /* shift the current digit, add in carry and store */
36 *tmpb-- = (*tmpa-- >> 1) | (r << (MP_DIGIT_BIT - 1));
37
38 /* forward carry to next iteration */
39 r = rr;
40 }
41
42 /* zero excess digits */
43 MP_ZERO_DIGITS(b->dp + b->used, oldused - b->used);
44
45 b->sign = a->sign;
46 mp_clamp(b);
47 return MP_OKAY;
48 }
49 #endif
50