signed short decode(unsigned char t)
{
  int exp = 0x8 - (0x7 & (t >> 4));
  int base = (0x1 << (exp+ 5)) - 34;
  int step = 0x1 << exp;
  signed short ret = base - step  * (0xf & t);
  ret = -ret - 1 +  (2 * ret + 1) * (t >> 7);
  return ret;
}