docs: function read_bits_n(buf, bl, n) {
  	var w = (bl&7), h = (bl>>>3), f = ((1<<n)-1);
  	var v = buf[h] >>> w;
  	if(n < 8 - w) return v & f;
  	v |= buf[h+1]<<(8-w);
  	if(n < 16 - w) return v & f;
  	v |= buf[h+2]<<(16-w);
  	if(n < 24 - w) return v & f;
  	v |= buf[h+3]<<(24-w);
  	return v & f;
  }