Extracts range bits. e.g. 0b00001100.extract(2..3) = 0b11 = 0x03.
0b00001100.extract(2..3) = 0b11 = 0x03
Create an Int mask of count length e.g. flatBitMask(3) = 0b00000111`.
count
Create a Long mask of count length e.g. flatLongBitMask(3) = 0b00000111L`.