NumSetBits

public class FindSetBits {
	
	public static int getTotalSetBits(byte[] b, int offset, int endIndex)
	{
		int size = b.length;
		length = endIndex - offset;
		if(offset > size*8) throw new IllegalArgumentException("Offset overflow");
		if((offset + length )> size*8) throw new IllegalArgumentException("Offset overflow");
		
		int startIndex = offset;
		int remLength = length;
		int totalBits = 0;
		
		while(startIndex < (offset+ length))
		{
			int byteIndex = startIndex/8;
			if(remLength >= 8 )
			{
				int len = 8 - startIndex%8;
				totalBits += getNumSetBits(b[byteIndex], startIndex%8, len);
				remLength -= len;
				startIndex += len;
			}
			else{
				totalBits += getNumSetBits(b[byteIndex], startIndex%8, remLength);
				break;
			}
		}
		
		return totalBits;
	}
	
	
	private static int getNumSetBits(byte b, int offset, int length)
	{
		if(offset + length > 8) throw new IllegalArgumentException("Length cannot exceed byte length ");
		int num = 0;
		for(int i = offset;i<=(offset+length); i++)
		{
			if( ((int)b&(1<<(8-i-1))) > 0)
					num++;
		}
		return num;
	}
	
}