Guint JBIG2HuffmanDecoder::readBits(Guint n) {
  Guint x, mask, nLeft;

  mask = (n == 32) ? 0xffffffff : ((1 << n) - 1);
  if (bufLen >= n) {
    x = (buf >> (bufLen - n)) & mask;
    bufLen -= n;
  } else {
    x = buf & ((1 << bufLen) - 1);
    nLeft = n - bufLen;
    bufLen = 0;
    while (nLeft >= 8) {
      x = (x << 8) | (str->getChar() & 0xff);
      nLeft -= 8;
    }
    if (nLeft > 0) {
      buf = str->getChar();
      bufLen = 8 - nLeft;
      x = (x << nLeft) | ((buf >> bufLen) & ((1 << nLeft) - 1));
    }
  }
  return x;
}

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