87 lines
2.2 KiB
C
87 lines
2.2 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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int pb_sub(pb_poly *a, pb_poly *b, pb_poly *c)
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{
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int neg, err, x, y, z, characteristic;
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pb_poly *tmp;
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/* grow c to be the max size */
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y = MAX(a->used, b->used);
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if (c->alloc < y) {
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if ((err = pb_grow(c, y)) != MP_OKAY) {
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return err;
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}
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}
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/* do we need to concern char */
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characteristic = mp_iszero(&(c->characteristic));
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/* sub the terms */
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z = MIN(a->used, b->used);
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for (x = 0; x < z; x++) {
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if ((err = mp_sub(&(a->terms[x]), &(b->terms[x]), &(c->terms[x]))) != MP_OKAY) {
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return err;
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}
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if (characteristic == MP_NO) {
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if ((err = mp_mod(&(c->terms[x]), &(c->characteristic), &(c->terms[x]))) != MP_OKAY) {
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return err;
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}
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}
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}
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/* excess digits? */
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if (y != z) {
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if (a->used == y) {
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tmp = a;
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neg = 0;
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} else {
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tmp = b;
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neg = 1;
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}
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for (x = z; x < y; x++) {
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if (characteristic == MP_NO) {
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if ((err = mp_mod(&(tmp->terms[x]), &(c->characteristic), &(c->terms[x]))) != MP_OKAY) {
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return err;
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}
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if (neg) {
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if ((err = mp_sub(&(c->characteristic), &(c->terms[x]), &(c->terms[x]))) != MP_OKAY) {
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return err;
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}
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}
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} else {
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if (neg) {
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if ((err = mp_neg(&(tmp->terms[x]), &(c->terms[x]))) != MP_OKAY) {
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return err;
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}
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} else {
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if ((err = mp_copy(&(tmp->terms[x]), &(c->terms[x]))) != MP_OKAY) {
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return err;
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}
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}
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}
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}
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}
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/* zero excess */
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for (x = y; x < c->used; x++) {
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mp_zero(&(c->terms[x]));
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}
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c->used = y;
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pb_clamp(c);
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return MP_OKAY;
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}
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