mirror of http://galexander.org/git/simplesshd.git
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
93 lines
2.1 KiB
93 lines
2.1 KiB
#include "tommath_private.h"
|
|
#ifdef BN_MP_GCD_C
|
|
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
|
|
/* SPDX-License-Identifier: Unlicense */
|
|
|
|
/* Greatest Common Divisor using the binary method */
|
|
mp_err mp_gcd(const mp_int *a, const mp_int *b, mp_int *c)
|
|
{
|
|
mp_int u, v;
|
|
int k, u_lsb, v_lsb;
|
|
mp_err err;
|
|
|
|
/* either zero than gcd is the largest */
|
|
if (MP_IS_ZERO(a)) {
|
|
return mp_abs(b, c);
|
|
}
|
|
if (MP_IS_ZERO(b)) {
|
|
return mp_abs(a, c);
|
|
}
|
|
|
|
/* get copies of a and b we can modify */
|
|
if ((err = mp_init_copy(&u, a)) != MP_OKAY) {
|
|
return err;
|
|
}
|
|
|
|
if ((err = mp_init_copy(&v, b)) != MP_OKAY) {
|
|
goto LBL_U;
|
|
}
|
|
|
|
/* must be positive for the remainder of the algorithm */
|
|
u.sign = v.sign = MP_ZPOS;
|
|
|
|
/* B1. Find the common power of two for u and v */
|
|
u_lsb = mp_cnt_lsb(&u);
|
|
v_lsb = mp_cnt_lsb(&v);
|
|
k = MP_MIN(u_lsb, v_lsb);
|
|
|
|
if (k > 0) {
|
|
/* divide the power of two out */
|
|
if ((err = mp_div_2d(&u, k, &u, NULL)) != MP_OKAY) {
|
|
goto LBL_V;
|
|
}
|
|
|
|
if ((err = mp_div_2d(&v, k, &v, NULL)) != MP_OKAY) {
|
|
goto LBL_V;
|
|
}
|
|
}
|
|
|
|
/* divide any remaining factors of two out */
|
|
if (u_lsb != k) {
|
|
if ((err = mp_div_2d(&u, u_lsb - k, &u, NULL)) != MP_OKAY) {
|
|
goto LBL_V;
|
|
}
|
|
}
|
|
|
|
if (v_lsb != k) {
|
|
if ((err = mp_div_2d(&v, v_lsb - k, &v, NULL)) != MP_OKAY) {
|
|
goto LBL_V;
|
|
}
|
|
}
|
|
|
|
while (!MP_IS_ZERO(&v)) {
|
|
/* make sure v is the largest */
|
|
if (mp_cmp_mag(&u, &v) == MP_GT) {
|
|
/* swap u and v to make sure v is >= u */
|
|
mp_exch(&u, &v);
|
|
}
|
|
|
|
/* subtract smallest from largest */
|
|
if ((err = s_mp_sub(&v, &u, &v)) != MP_OKAY) {
|
|
goto LBL_V;
|
|
}
|
|
|
|
/* Divide out all factors of two */
|
|
if ((err = mp_div_2d(&v, mp_cnt_lsb(&v), &v, NULL)) != MP_OKAY) {
|
|
goto LBL_V;
|
|
}
|
|
}
|
|
|
|
/* multiply by 2**k which we divided out at the beginning */
|
|
if ((err = mp_mul_2d(&u, k, c)) != MP_OKAY) {
|
|
goto LBL_V;
|
|
}
|
|
c->sign = MP_ZPOS;
|
|
err = MP_OKAY;
|
|
LBL_V:
|
|
mp_clear(&u);
|
|
LBL_U:
|
|
mp_clear(&v);
|
|
return err;
|
|
}
|
|
#endif
|