denyhosts/clamav/libclamav/tomsfastmath/numtheory/fp_gcd.c

56 lines
1.1 KiB
C

/* TomsFastMath, a fast ISO C bignum library.
*
* This project is meant to fill in where LibTomMath
* falls short. That is speed ;-)
*
* This project is public domain and free for all purposes.
*
* Tom St Denis, tomstdenis@gmail.com
*/
#include <tfm_private.h>
/* c = (a, b) */
void fp_gcd(fp_int *a, fp_int *b, fp_int *c)
{
fp_int u, v, r;
/* either zero than gcd is the largest */
if (fp_iszero (a) == 1 && fp_iszero (b) == 0) {
fp_abs (b, c);
return;
}
if (fp_iszero (a) == 0 && fp_iszero (b) == 1) {
fp_abs (a, c);
return;
}
/* optimized. At this point if a == 0 then
* b must equal zero too
*/
if (fp_iszero (a) == 1) {
fp_zero(c);
return;
}
/* sort inputs */
if (fp_cmp_mag(a, b) != FP_LT) {
fp_init_copy(&u, a);
fp_init_copy(&v, b);
} else {
fp_init_copy(&u, b);
fp_init_copy(&v, a);
}
fp_zero(&r);
while (fp_iszero(&v) == FP_NO) {
fp_mod(&u, &v, &r);
fp_copy(&v, &u);
fp_copy(&r, &v);
}
fp_copy(&u, c);
}
/* $Source$ */
/* $Revision$ */
/* $Date$ */