calc_enc_length (gnutls_session_t session, int data_size,
		 int hash_size, uint8_t * pad, int random_pad,
		 cipher_type_t block_algo, uint16_t blocksize)
{
  uint8_t rnd;
  int length, ret;

  *pad = 0;

  switch (block_algo)
    {
    case CIPHER_STREAM:
      length = data_size + hash_size;

      break;
    case CIPHER_BLOCK:
      ret =_gnutls_rnd (RND_NONCE, &rnd, 1);
      if ( ret < 0)
	{
	  gnutls_assert ();
	  return ret;
	}

      /* make rnd a multiple of blocksize */
      if (session->security_parameters.version == GNUTLS_SSL3 ||
	  random_pad == 0)
	{
	  rnd = 0;
	}
      else
	{
	  rnd = (rnd / blocksize) * blocksize;
	  /* added to avoid the case of pad calculated 0
	   * seen below for pad calculation.
	   */
	  if (rnd > blocksize)
	    rnd -= blocksize;
	}

      length = data_size + hash_size;

      *pad = (uint8_t) (blocksize - (length % blocksize)) + rnd;

      length += *pad;
      if (session->security_parameters.version >= GNUTLS_TLS1_1)
	length += blocksize;	/* for the IV */

      break;
    default:
      gnutls_assert ();
      return GNUTLS_E_INTERNAL_ERROR;
    }

  return length;
}

This weakness involves numeric computation errors, such as integer overflows, underflows, or precision losses, which can lead to miscalculations and exploitable behaviors in software.