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#include "tommath_private.h"
#ifdef BN_MP_REDUCE_2K_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
/* reduces a modulo n where n is of the form 2**p - d */
mp_err mp_reduce_2k(mp_int *a, const mp_int *n, mp_digit d)
{
mp_int q;
mp_err err;
int p;
if ((err = mp_init(&q)) != MP_OKAY) {
return err;
}
p = mp_count_bits(n);
top:
/* q = a/2**p, a = a mod 2**p */
if ((err = mp_div_2d(a, p, &q, a)) != MP_OKAY) {
goto LBL_ERR;
}
if (d != 1u) {
/* q = q * d */
if ((err = mp_mul_d(&q, d, &q)) != MP_OKAY) {
goto LBL_ERR;
}
}
/* a = a + q */
if ((err = s_mp_add(a, &q, a)) != MP_OKAY) {
goto LBL_ERR;
}
if (mp_cmp_mag(a, n) != MP_LT) {
if ((err = s_mp_sub(a, n, a)) != MP_OKAY) {
goto LBL_ERR;
}
goto top;
}
LBL_ERR:
mp_clear(&q);
return err;
}
#endif
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