pb_rshd.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_rshd(pb_poly *a, int x)
  15 {
  16    int y;
  17
  18    if (x >= a->used) {
  19       pb_zero(a);
  20       return MP_OKAY;
  21    }
  22
  23    if (x <= 0) {
  24       return MP_OKAY;
  25    }
  26
  27    for (y = x; y < a->used; y++) {
  28        mp_exch(&(a->terms[y]), &(a->terms[y-x]));
  29    }
  30
  31    for (y = a->used - x; y < a->used; y++) {
  32        mp_zero(&(a->terms[y]));
  33    }
  34    a->used -= x;
  35
  36    return MP_OKAY;
  37 }
  38