hash(int length) {
    int startoffset, offset, count;

    if (length > 127) {
	length >>= 3;
	length &= ~3;
	startoffset = offset = length;
	count = 7;
    } else {
	length -= 4;
	count = length >> 4;
	startoffset = (length & 12) + 4;
	offset = 16;
    }
    f(startoffset, offset, count);
}