Bitposition

In computing, a bit position refers to the ordinal position of a binary digit within a word, byte, or stream. It is most often used to describe the index of a set bit (1) or to specify the location where a particular bit is accessed or modified. Bit positions are inherently tied to the chosen word size (for example, 8, 16, 32, or 64 bits). The term bitposition is sometimes used as a single word.

Convention for numbering varies: many contexts use zero-based indexing from the least significant bit, so the LSB has position 0 and the MSB has position N-1 for an N-bit word. Other contexts label bits from the most significant end or use one-based numbering; always check the documentation.

Common operations involve determining or manipulating bit positions. To find the position of the least significant 1, programs compute the trailing zero count (ctz); the position of the most significant 1 uses the leading zero count (clz) or a bit-length calculation. Isolating the lowest set bit can be done with x & -x. Languages and CPUs expose built-in intrinsics such as ctz, clz, or BitScanForward/BitScanReverse to perform these tasks efficiently.

Bit positions underpin many techniques in systems and applications: bitboards in board games, bitfields in data structures, encoding schemes, and fast indexing in compressed or packed data. They are also used in algorithms for firewall rules, network protocols, and error detection where specific bit positions carry meaning.

Understanding the bit position of a value is a fundamental skill in low-level programming, enabling compact storage and high-performance bitwise operations.