pb_mul.c

   1 /* LibTomPoly, Polynomial Basis Math -- Tom St Denis
   2  *
   3  * LibTomPoly is a public domain library that provides
   4  * polynomial basis arithmetic support.  It relies on
   5  * LibTomMath for large integer support.
   6  *
   7  * This library is free for all purposes without any
   8  * express guarantee that it works.
   9  *
  10  * Tom St Denis, tomstdenis@iahu.ca, http://poly.libtomcrypt.org
  11  */
  12 #include <tompoly.h>
  13
  14 int pb_mul(pb_poly *a, pb_poly *b, pb_poly *c)
  15 {
  16    int err, x, y;
  17    pb_poly tmp;
  18    mp_int  tmp2;
  19
  20    /* make temp */
  21    if ((err = pb_init_size(&tmp, &(c->characteristic), a->used + b->used)) != MP_OKAY) {
  22       return err;
  23    }
  24
  25    if ((err = mp_init(&tmp2)) != MP_OKAY) {
  26       goto __TMP;
  27    }
  28
  29    /* multiply the terms */
  30    for (x = 0; x < a->used; x++) {
  31        for (y = 0; y < b->used; y++) {
  32            if ((err = mp_mul(&(a->terms[x]), &(b->terms[y]), &tmp2)) != MP_OKAY) {
  33               goto __TMP2;
  34            }
  35            if ((err = mp_add(&tmp2, &(tmp.terms[x+y]), &(tmp.terms[x+y]))) != MP_OKAY) {
  36               goto __TMP2;
  37            }
  38        }
  39    }
  40
  41    /* now reduce the terms as required */
  42    if (mp_iszero(&(c->characteristic)) == MP_NO) {
  43       for (x = 0; x < (a->used + b->used); x++) {
  44           if ((err = mp_mod(&(tmp.terms[x]), &(c->characteristic), &(tmp.terms[x]))) != MP_OKAY) {
  45              goto __TMP2;
  46           }
  47       }
  48    }
  49
  50    /* set digit count */
  51    tmp.used = a->used + b->used;
  52    pb_clamp(&tmp);
  53
  54    /* exchange tmp and c */
  55    pb_exch(&tmp, c);
  56
  57    err = MP_OKAY;
  58
  59 __TMP2:  mp_clear(&tmp2);
  60 __TMP :  pb_clear(&tmp);
  61    return err;
  62 }