mirror of
http://galexander.org/git/simplesshd.git
synced 2024-11-27 17:58:13 +00:00
106 lines
2.6 KiB
C
106 lines
2.6 KiB
C
#include <tommath.h>
|
|
#ifdef BN_MP_GCD_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.
|
|
*
|
|
* The library is free for all purposes without any express
|
|
* guarantee it works.
|
|
*
|
|
* Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com
|
|
*/
|
|
|
|
/* Greatest Common Divisor using the binary method */
|
|
int mp_gcd (mp_int * a, mp_int * b, mp_int * c)
|
|
{
|
|
mp_int u, v;
|
|
int k, u_lsb, v_lsb, res;
|
|
|
|
/* either zero than gcd is the largest */
|
|
if (mp_iszero (a) == MP_YES) {
|
|
return mp_abs (b, c);
|
|
}
|
|
if (mp_iszero (b) == MP_YES) {
|
|
return mp_abs (a, c);
|
|
}
|
|
|
|
/* get copies of a and b we can modify */
|
|
if ((res = mp_init_copy (&u, a)) != MP_OKAY) {
|
|
return res;
|
|
}
|
|
|
|
if ((res = 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 = MIN(u_lsb, v_lsb);
|
|
|
|
if (k > 0) {
|
|
/* divide the power of two out */
|
|
if ((res = mp_div_2d(&u, k, &u, NULL)) != MP_OKAY) {
|
|
goto LBL_V;
|
|
}
|
|
|
|
if ((res = mp_div_2d(&v, k, &v, NULL)) != MP_OKAY) {
|
|
goto LBL_V;
|
|
}
|
|
}
|
|
|
|
/* divide any remaining factors of two out */
|
|
if (u_lsb != k) {
|
|
if ((res = mp_div_2d(&u, u_lsb - k, &u, NULL)) != MP_OKAY) {
|
|
goto LBL_V;
|
|
}
|
|
}
|
|
|
|
if (v_lsb != k) {
|
|
if ((res = mp_div_2d(&v, v_lsb - k, &v, NULL)) != MP_OKAY) {
|
|
goto LBL_V;
|
|
}
|
|
}
|
|
|
|
while (mp_iszero(&v) == 0) {
|
|
/* 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 ((res = s_mp_sub(&v, &u, &v)) != MP_OKAY) {
|
|
goto LBL_V;
|
|
}
|
|
|
|
/* Divide out all factors of two */
|
|
if ((res = 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 ((res = mp_mul_2d (&u, k, c)) != MP_OKAY) {
|
|
goto LBL_V;
|
|
}
|
|
c->sign = MP_ZPOS;
|
|
res = MP_OKAY;
|
|
LBL_V:mp_clear (&u);
|
|
LBL_U:mp_clear (&v);
|
|
return res;
|
|
}
|
|
#endif
|
|
|
|
/* $Source: /cvs/libtom/libtommath/bn_mp_gcd.c,v $ */
|
|
/* $Revision: 1.4 $ */
|
|
/* $Date: 2006/03/31 14:18:44 $ */
|