60 lines
1.6 KiB
C
60 lines
1.6 KiB
C
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/* 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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/* is a(x) irreducible? */
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int pb_isirreduc(pb_poly *a, int *res)
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{
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pb_poly u, tmp, fm, d;
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int err, i;
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/* default to no */
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*res = MP_NO;
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/* init temps */
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if ((err = pb_init_multi(&(a->characteristic),
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&u, &tmp, &fm, &d, NULL)) != MP_OKAY) {
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return err;
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}
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/* fm = monic(a(x)) */
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if ((err = pb_monic(a, &fm)) != MP_OKAY) { goto _ERR; }
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/* u = x */
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mp_set(&(u.terms[1]), 1); u.used = 2;
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/* loop */
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for (i = 1; i <= (a->used / 2); i++) {
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/* u = u^p mod fm */
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if ((err = pb_exptmod(&u, &(a->characteristic), &fm, &u)) != MP_OKAY) { goto _ERR; }
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/* tmp = u - x */
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pb_zero(&tmp);
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mp_set(&(tmp.terms[1]), 1); tmp.used = 2;
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if ((err = pb_sub(&u, &tmp, &tmp)) != MP_OKAY) { goto _ERR; }
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/* d = gcd(fm, tmp) */
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if ((err = pb_gcd(&fm, &tmp, &d)) != MP_OKAY) { goto _ERR; }
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/* if d != 1 then reducible */
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if (d.used > 1) { err = MP_OKAY; goto _ERR; }
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}
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/* irreducible */
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*res = MP_YES;
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err = MP_OKAY;
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_ERR: pb_clear_multi(&u, &tmp, &fm, &d, NULL);
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return err;
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}
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