61 lines
1.5 KiB
C
61 lines
1.5 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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/* makes b equal to the monic polynomial form of a */
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int pb_monic(pb_poly *a, pb_poly *b)
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{
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mp_int tmp;
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int err, x;
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/* must be in GF(p)[x] */
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if (mp_iszero(&(b->characteristic)) == MP_YES) {
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return MP_VAL;
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}
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/* if it's already monic just copy */
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if (a->used == 0 || mp_cmp_d(&(a->terms[a->used - 1]), 1) == MP_EQ) {
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return pb_copy(a, b);
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}
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/* grow b to hold result */
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if (b->alloc < a->used) {
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if ((err = pb_grow(b, a->used)) != MP_OKAY) {
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return err;
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}
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}
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/* now init tmp and find the inverse of the leading digit */
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if ((err = mp_init(&tmp)) != MP_OKAY) {
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return err;
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}
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if ((err = mp_invmod(&(a->terms[a->used-1]), &(b->characteristic), &tmp)) != MP_OKAY) { goto _ERR; }
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/* now reduce each coefficient */
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for (x = 0; x < a->used; x++) {
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if ((err = mp_mulmod(&(a->terms[x]), &tmp, &(b->characteristic), &(b->terms[x]))) != MP_OKAY) { goto _ERR; }
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}
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/* zero excess digits */
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for (x = a->used; x < b->used; x++) {
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mp_zero(&(b->terms[x]));
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}
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b->used = a->used;
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err = MP_OKAY;
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_ERR: mp_clear(&tmp);
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return err;
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}
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