pb_readraw.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_readraw(pb_poly *a, unsigned char *buf, int len)
  15 {
  16    int terms, x, y, z, err;
  17
  18    /* zero poly */
  19    pb_zero(a);
  20
  21    /* must be at least four bytes */
  22    if (len < 4) {
  23       return MP_VAL;
  24    }
  25
  26    /* number of terms */
  27    terms = ((unsigned)buf[0]) | ((unsigned)buf[1]<<8);
  28    y     = 2;
  29
  30    /* grow to the right size */
  31    if (a->alloc < terms) {
  32       if ((err = pb_grow(a, terms)) != MP_OKAY) {
  33          return err;
  34       }
  35    }
  36
  37    /* read characteristic */
  38    z = ((unsigned)buf[y]) | ((unsigned)buf[y+1]<<8); y += 2;
  39    if (z + y > len)                                                                   { return MP_VAL; }
  40    if ((err = mp_read_signed_bin(&(a->characteristic), buf+y, z)) != MP_OKAY)         { return err; }
  41    y += z;
  42
  43
  44    /* read terms */
  45    for (x = 0; x < terms; x++) {
  46       z = ((unsigned)buf[y]) | ((unsigned)buf[y+1]<<8); y += 2;
  47       if (z + y > len)                                                                { return MP_VAL; }
  48       if ((err = mp_read_signed_bin(&(a->characteristic), buf+y, z)) != MP_OKAY)      { return err; }
  49       y += z;
  50    }
  51
  52    return MP_OKAY;
  53 }
  54
  55