CRC16CCITT

CRC16-CCITT is a family of 16-bit cyclic redundancy checks based on the ITU-T CRC-16 polynomial 0x1021 (x^16 + x^12 + x^5 + 1). It is widely used for error detection in telecommunications protocols, data framing, and storage where a compact checksum is desired. Implementations compute the remainder of the polynomial division of the input bit stream by 0x1021, either bit by bit or with a precomputed lookup table. Most variants differ in initial value, reflection of input and output, and final xor value, which changes the detected-error properties for particular use cases.

Common variants include CRC-16/CCITT-FALSE (poly 0x1021, init 0xFFFF, refin false, refout false, xorout 0x0000), CRC-16/XMODEM (poly 0x1021, init 0x0000, refin false, refout false, xorout 0x0000), CRC-16/X25 (poly 0x1021, init 0xFFFF, refin true, refout true, xorout 0xFFFF), CRC-16/KERMIT (poly 0x1021, init 0x0000, refin true, refout true, xorout 0x0000), and CRC-16/CCITT (ITU-T) (poly 0x1021, init 0x1D0F, refin false, refout false, xorout 0x0000). Each variant has different suitability for particular protocols and error-detection requirements.

Applications of CRC-16-CCITT appear in telecommunications and data protocols where a balance between computational efficiency and error-detection capability is desired. Implementations can be hardware- or software-based and are commonly optimized with table-driven approaches for speed.