pqc/external/libtompoly-0.04/pb_gcd.c

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2014-04-14 20:22:07 +00:00
/* LibTomPoly, Polynomial Basis Math -- Tom St Denis
*
* LibTomPoly is a public domain library that provides
* polynomial basis arithmetic support. It relies on
* LibTomMath for large integer support.
*
* This library is free for all purposes without any
* express guarantee that it works.
*
* Tom St Denis, tomstdenis@iahu.ca, http://poly.libtomcrypt.org
*/
#include <tompoly.h>
/* returns the monic GCD only for GF(p^k)[x] */
int pb_gcd(pb_poly *a, pb_poly *b, pb_poly *c)
{
pb_poly A, B, tmp;
int err;
if (mp_iszero(&(c->characteristic)) == MP_YES) {
return MP_VAL;
}
/* special cases (one or both are zero) */
if (a->used == 0 && b->used == 0) {
/* both zero, set to 1 */
pb_zero(c);
c->used = 1;
mp_set(&(c->terms[0]), 1);
return MP_OKAY;
} else if (a->used == 0) {
return pb_copy(b, c);
} else if (b->used == 0) {
return pb_copy(a, c);
}
if ((err = pb_init(&tmp, &(c->characteristic))) != MP_OKAY) {
return err;
}
if ((err = pb_init_copy(&A, a)) != MP_OKAY) {
goto __TMP;
}
if ((err = pb_init_copy(&B, b)) != MP_OKAY) {
goto __A;
}
while (B.used > 0) {
if ((err = pb_mod(&A, &B, &tmp)) != MP_OKAY) {
goto __B;
}
/* A = B, B = tmp */
if ((err = pb_copy(&B, &A)) != MP_OKAY) {
goto __B;
}
if ((err = pb_copy(&tmp, &B)) != MP_OKAY) {
goto __B;
}
}
/* ensure it's monic */
err = pb_monic(&A, c);
__B : pb_clear(&B);
__A : pb_clear(&A);
__TMP: pb_clear(&tmp);
return err;
}