Lownibble

Lownibble is a term used in computing to refer to the lower nibble of a byte, meaning the least significant four bits. A nibble is half a byte, capable of representing 16 distinct values (0 to 15). In an eight-bit byte, the high nibble comprises the most significant four bits (bits 4–7) and the low nibble comprises the least significant four bits (bits 0–3).

The low nibble is commonly isolated and manipulated using bitwise operations. For an 8-bit value x, the low nibble can be extracted as x & 0x0F (or x & 15). To obtain the high nibble, one can use (x >> 4) & 0x0F. These operations are widely used in low-level programming, especially when two 4-bit quantities are packed into a single byte or when decimal digits encoded in binary Coded Decimal (BCD) are processed.

Practical uses of the low nibble include digit extraction, compact data packing, and nibble-wise arithmetic in resource-constrained environments. In BCD, each nibble represents a decimal digit, typically with the low nibble corresponding to the units digit. The concept of a low nibble is often paired with the high nibble, with both nibbles together forming the full byte.

See also: high nibble, nibble, bitwise operations, binary-coded decimal.