pb_add.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_add(pb_poly *a, pb_poly *b, pb_poly *c)
  15 {
  16    int err, x, y, z, characteristic;
  17    pb_poly *tmp;
  18
  19    /* grow c to be the max size */
  20    y = MAX(a->used, b->used);
  21    if (c->alloc < y) {
  22       if ((err = pb_grow(c, y)) != MP_OKAY) {
  23          return err;
  24       }
  25    }
  26
  27    /* do we need to concern char */
  28    characteristic = mp_iszero(&(c->characteristic));
  29
  30    /* add the terms */
  31    z = MIN(a->used, b->used);
  32    for (x = 0; x < z; x++) {
  33        if ((err = mp_add(&(a->terms[x]), &(b->terms[x]), &(c->terms[x]))) != MP_OKAY) {
  34           return err;
  35        }
  36        if (characteristic == MP_NO) {
  37           if ((err = mp_mod(&(c->terms[x]), &(c->characteristic), &(c->terms[x]))) != MP_OKAY) {
  38              return err;
  39           }
  40        }
  41    }
  42
  43    /* excess digits? */
  44    if (y != z) {
  45        if (a->used == y) {
  46           tmp = a;
  47        } else {
  48           tmp = b;
  49        }
  50        for (x = z; x < y; x++) {
  51           if (characteristic == MP_NO) {
  52              if ((err = mp_mod(&(tmp->terms[x]), &(c->characteristic), &(c->terms[x]))) != MP_OKAY) {
  53                 return err;
  54              }
  55           } else {
  56              if ((err = mp_copy(&(tmp->terms[x]), &(c->terms[x]))) != MP_OKAY) {
  57                 return err;
  58              }
  59           }
  60        }
  61    }
  62
  63    /* zero excess */
  64    for (x = y; x < c->used; x++) {
  65        mp_zero(&(c->terms[x]));
  66    }
  67    c->used = y;
  68    pb_clamp(c);
  69
  70    return MP_OKAY;
  71 }
  72
  73