61 lines
1.3 KiB
C
61 lines
1.3 KiB
C
#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: $Format:%ai$ */
|