CRC-16 Checksum (crc16)

CRC-16 cyclic redundancy check, using the CRC-16/XMODEM algorithm standard. Chainable by feeding the previous CRC output as the initial value.

Algorithm Parameters

Parameter	Value
Name	CRC-16/XMODEM
Polynomial	0x1021 (x¹⁶ + x¹² + x⁵ + 1)
Init	0x0000
RefIn	False
RefOut	False
XorOut	0x0000
Check	"123456789" → 0x31C3

API

uint16_t crc16_sum(uint16_t crc, const uint8_t * buf, int len);

• crc — Initial value (typically 0 for the first call)
• buf — Data buffer
• len — Data length

Returns the CRC-16 checksum.

Example

Single Checksum

uint8_t msg[] = { 'x', 'b', 'o', 'o', 't' };
uint16_t checksum = crc16_sum(0, msg, sizeof(msg));
/* checksum = 0x394c */

Chained Calls

uint8_t part1[] = { 0x01, 0x02 };
uint8_t part2[] = { 0x03, 0x04 };
uint16_t crc = crc16_sum(0, part1, sizeof(part1));
crc = crc16_sum(crc, part2, sizeof(part2));