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