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
|
#include "tommath_private.h"
#ifdef BN_MP_REDUCE_2K_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
* LibTomMath is a library that provides multiple-precision
* integer arithmetic as well as number theoretic functionality.
*
* The library was designed directly after the MPI library by
* Michael Fromberger but has been written from scratch with
* additional optimizations in place.
*
* SPDX-License-Identifier: Unlicense
*/
/* reduces a modulo n where n is of the form 2**p - d */
int mp_reduce_2k(mp_int *a, const mp_int *n, mp_digit d)
{
mp_int q;
int p, res;
if ((res = mp_init(&q)) != MP_OKAY) {
return res;
}
p = mp_count_bits(n);
top:
/* q = a/2**p, a = a mod 2**p */
if ((res = mp_div_2d(a, p, &q, a)) != MP_OKAY) {
goto LBL_ERR;
}
if (d != 1u) {
/* q = q * d */
if ((res = mp_mul_d(&q, d, &q)) != MP_OKAY) {
goto LBL_ERR;
}
}
/* a = a + q */
if ((res = s_mp_add(a, &q, a)) != MP_OKAY) {
goto LBL_ERR;
}
if (mp_cmp_mag(a, n) != MP_LT) {
if ((res = s_mp_sub(a, n, a)) != MP_OKAY) {
goto LBL_ERR;
}
goto top;
}
LBL_ERR:
mp_clear(&q);
return res;
}
#endif
/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */
|
