pqc/external/libtompoly-0.04/pb_add.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>
int pb_add(pb_poly *a, pb_poly *b, pb_poly *c)
{
int err, x, y, z, characteristic;
pb_poly *tmp;
/* grow c to be the max size */
y = MAX(a->used, b->used);
if (c->alloc < y) {
if ((err = pb_grow(c, y)) != MP_OKAY) {
return err;
}
}
/* do we need to concern char */
characteristic = mp_iszero(&(c->characteristic));
/* add the terms */
z = MIN(a->used, b->used);
for (x = 0; x < z; x++) {
if ((err = mp_add(&(a->terms[x]), &(b->terms[x]), &(c->terms[x]))) != MP_OKAY) {
return err;
}
if (characteristic == MP_NO) {
if ((err = mp_mod(&(c->terms[x]), &(c->characteristic), &(c->terms[x]))) != MP_OKAY) {
return err;
}
}
}
/* excess digits? */
if (y != z) {
if (a->used == y) {
tmp = a;
} else {
tmp = b;
}
for (x = z; x < y; x++) {
if (characteristic == MP_NO) {
if ((err = mp_mod(&(tmp->terms[x]), &(c->characteristic), &(c->terms[x]))) != MP_OKAY) {
return err;
}
} else {
if ((err = mp_copy(&(tmp->terms[x]), &(c->terms[x]))) != MP_OKAY) {
return err;
}
}
}
}
/* zero excess */
for (x = y; x < c->used; x++) {
mp_zero(&(c->terms[x]));
}
c->used = y;
pb_clamp(c);
return MP_OKAY;
}