private boolean isMaskOn() {
		// translate bit positions to change 0 to mean the most significant bit for internal use
		int totalBitLength = bytes.length * 4;
		int start = totalBitLength - endBit - 1;
		int end = totalBitLength - startBit - 1;

		int startByte = start / 8;
		int endByte = end / 8;
		int bitInStartByte = start % 8;
		int bitInEndByte = end % 8;

		if (startByte == endByte) {
			int mask = START_BYTE_MASK[bitInStartByte] & END_BYTE_MASK[bitInEndByte];
			return (bytes[startByte] & mask) == mask;
		}

		if ((bytes[startByte] & START_BYTE_MASK[bitInStartByte]) != START_BYTE_MASK[bitInStartByte]) {
			return false;
		}

		if ((bytes[endByte] & END_BYTE_MASK[bitInEndByte]) != END_BYTE_MASK[bitInEndByte]) {
			return false;
		}
		for (int i = startByte + 1; i < endByte; i++) {
			if (bytes[i] != -1) {
				return false;
			}
		}

		return true;
	}
Tests if the all the mask bits from startBit (least significant bit) to endBit (most significant bit)
are on.
@param startBit the least significant bit position 
@param endBit the most significant bit position
@return true if all mask bits from startBit to endBit are on.
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/model/lang/RegisterValue.java