pb_lshd.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_lshd(pb_poly *a, int x)
  15 {
  16    int err, y;
  17
  18    if (x <= 0) {
  19       return MP_OKAY;
  20    }
  21
  22    /* grow as required */
  23    if (a->alloc < (a->used + x)) {
  24       if ((err = pb_grow(a, a->used + x)) != MP_OKAY) {
  25          return err;
  26       }
  27    }
  28
  29    /* shift */
  30    for (y = a->used + x; y >= x; y--) {
  31        mp_exch(&(a->terms[y-x]), &(a->terms[y]));
  32    }
  33
  34    /* zero lower digits */
  35    for (y = 0; y < x; y++) {
  36        mp_zero(&(a->terms[y]));
  37    }
  38    a->used += x;
  39
  40    return MP_OKAY;
  41 }
  42