CRC-16 / NRSC-5

/* 
 * Model: CRC-16 / NRSC-5 (16-bit)
 * Poly: 0x080B, Init: 0xFFFF, XorOut: 0x0000
 * CRC Table C Source Code & Lookup Table Generator
 */
#include <stdint.h>
#include <stddef.h>

const uint16_t crc_table[256] = {
  0x0000, 0x35A4, 0x6B48, 0x5EEC, 0xD690, 0xE334, 0xBDD8, 0x887C, 
  0x0D01, 0x38A5, 0x6649, 0x53ED, 0xDB91, 0xEE35, 0xB0D9, 0x857D, 
  0x1A02, 0x2FA6, 0x714A, 0x44EE, 0xCC92, 0xF936, 0xA7DA, 0x927E, 
  0x1703, 0x22A7, 0x7C4B, 0x49EF, 0xC193, 0xF437, 0xAADB, 0x9F7F, 
  0x3404, 0x01A0, 0x5F4C, 0x6AE8, 0xE294, 0xD730, 0x89DC, 0xBC78, 
  0x3905, 0x0CA1, 0x524D, 0x67E9, 0xEF95, 0xDA31, 0x84DD, 0xB179, 
  0x2E06, 0x1BA2, 0x454E, 0x70EA, 0xF896, 0xCD32, 0x93DE, 0xA67A, 
  0x2307, 0x16A3, 0x484F, 0x7DEB, 0xF597, 0xC033, 0x9EDF, 0xAB7B, 
  0x6808, 0x5DAC, 0x0340, 0x36E4, 0xBE98, 0x8B3C, 0xD5D0, 0xE074, 
  0x6509, 0x50AD, 0x0E41, 0x3BE5, 0xB399, 0x863D, 0xD8D1, 0xED75, 
  0x720A, 0x47AE, 0x1942, 0x2CE6, 0xA49A, 0x913E, 0xCFD2, 0xFA76, 
  0x7F0B, 0x4AAF, 0x1443, 0x21E7, 0xA99B, 0x9C3F, 0xC2D3, 0xF777, 
  0x5C0C, 0x69A8, 0x3744, 0x02E0, 0x8A9C, 0xBF38, 0xE1D4, 0xD470, 
  0x510D, 0x64A9, 0x3A45, 0x0FE1, 0x879D, 0xB239, 0xECD5, 0xD971, 
  0x460E, 0x73AA, 0x2D46, 0x18E2, 0x909E, 0xA53A, 0xFBD6, 0xCE72, 
  0x4B0F, 0x7EAB, 0x2047, 0x15E3, 0x9D9F, 0xA83B, 0xF6D7, 0xC373, 
  0xD010, 0xE5B4, 0xBB58, 0x8EFC, 0x0680, 0x3324, 0x6DC8, 0x586C, 
  0xDD11, 0xE8B5, 0xB659, 0x83FD, 0x0B81, 0x3E25, 0x60C9, 0x556D, 
  0xCA12, 0xFFB6, 0xA15A, 0x94FE, 0x1C82, 0x2926, 0x77CA, 0x426E, 
  0xC713, 0xF2B7, 0xAC5B, 0x99FF, 0x1183, 0x2427, 0x7ACB, 0x4F6F, 
  0xE414, 0xD1B0, 0x8F5C, 0xBAF8, 0x3284, 0x0720, 0x59CC, 0x6C68, 
  0xE915, 0xDCB1, 0x825D, 0xB7F9, 0x3F85, 0x0A21, 0x54CD, 0x6169, 
  0xFE16, 0xCBB2, 0x955E, 0xA0FA, 0x2886, 0x1D22, 0x43CE, 0x766A, 
  0xF317, 0xC6B3, 0x985F, 0xADFB, 0x2587, 0x1023, 0x4ECF, 0x7B6B, 
  0xB818, 0x8DBC, 0xD350, 0xE6F4, 0x6E88, 0x5B2C, 0x05C0, 0x3064, 
  0xB519, 0x80BD, 0xDE51, 0xEBF5, 0x6389, 0x562D, 0x08C1, 0x3D65, 
  0xA21A, 0x97BE, 0xC952, 0xFCF6, 0x748A, 0x412E, 0x1FC2, 0x2A66, 
  0xAF1B, 0x9ABF, 0xC453, 0xF1F7, 0x798B, 0x4C2F, 0x12C3, 0x2767, 
  0x8C1C, 0xB9B8, 0xE754, 0xD2F0, 0x5A8C, 0x6F28, 0x31C4, 0x0460, 
  0x811D, 0xB4B9, 0xEA55, 0xDFF1, 0x578D, 0x6229, 0x3CC5, 0x0961, 
  0x961E, 0xA3BA, 0xFD56, 0xC8F2, 0x408E, 0x752A, 0x2BC6, 0x1E62, 
  0x9B1F, 0xAEBB, 0xF057, 0xC5F3, 0x4D8F, 0x782B, 0x26C7, 0x1363
};

uint16_t calculate_crc(const uint8_t *data, size_t length) {
    uint16_t crc = 0xFFFF;
    for (size_t i = 0; i < length; i++) {
        #if 1
        uint8_t idx = (uint8_t)(crc ^ data[i]);
        crc = (crc >> 8) ^ crc_table[idx];
        #else
        uint8_t idx = (uint8_t)((crc >> 8) ^ data[i]);
        crc = (crc << 8) ^ crc_table[idx];
        #endif
    }
    return crc ^ 0x0000;
}