CRC16IBM

CRC16IBM refers to the 16-bit cyclic redundancy check commonly known as CRC-16-IBM. It is also known by names such as CRC-16-ANSI and IBM-SDLC and has historically been used to detect accidental data corruption in communication protocols and storage systems. The variant is defined by a specific polynomial and bit-ordering that influence how the checksum is computed and verified.

The standard parameters for CRC16IBM are a width of 16 bits, a polynomial of 0x8005 (binary 1000000000000101), an initial value of 0x0000, and a final xor value of 0x0000. The algorithm is typically implemented with refin (input reflected) and refout (output reflected) set to true, meaning bit processing is performed least-significant-bit first. In its reflected form, the polynomial can be represented as 0xA001, which is the bitwise inverse of 0x8005 under reflection.

Implementation approaches can vary, but common methods include a bitwise non-table approach or a table-driven approach using a 256-entry table of 16-bit values. Table-driven implementations are generally faster and are widely available in software libraries for compatibility with legacy systems. The reflected nature of the algorithm affects how data is fed into the computation and how the resulting CRC is interpreted.

Applications and history: CRC16IBM has been used in IBM-era data link controls and other legacy protocols, including early SDLC/HDLC contexts. While many modern protocols use different CRC standards, the CRC-16-IBM variant remains relevant for compatibility with existing systems and data sets that rely on the 0x8005 polynomial with reflected processing.

See also: CRC-16-ANSI, CRC-16-IBM-SDLC, CRC-16-CCITT.