read specified bits in byteArray

readBits.as

/**
* study from byteArray.org(about a as3 byteArray's Book)
*/
import flash.utils.ByteArray;

var b:ByteArray = new ByteArray();
b.writeUnsignedInt(1234);
b.writeUnsignedInt(uint.MAX_VALUE);
b.position = 0;

trace(b.readUnsignedInt().toString(2)); //0100, 1101, 0010 (unSignedInt are all 32 bits, use zero for padding)
trace(b.readUnsignedInt().toString(2)); //1111, 1111, 1111 (unSignedInt are all 32 bits, use one for padding)

b.position = 0; //set position to zero

b.readUnsignedByte(); //ignore a byte(8 bits)
b.readUnsignedByte(); //ignore a byte(8 bits)
b.readUnsignedByte(); //ignore a byte(8 bits)

trace(readBits(b, 13).toString(2));
//1101, 0010, 11111 // we get 13 bits in byteArray

/**
* readBits in byteArray
*/
function readBits(b:ByteArray, bitsNum:int):int{
	var c:uint = b.readUnsignedByte();
	var point:int = 0;
	var s:uint = 0;
	var result:uint = 0;
	for(var i:int = 0; i < bitsNum; i ++){
		s = ((1 << (7 - point)) & c) >>> (7 - point);
		result |= (s << (bitsNum - 1) - i);
		if(++point == 8){
			point = 0;
			c = b.readUnsignedByte();
		}
	}
	return result;
}