CRC-16 / PROFIBUS

/* 
 * Model: CRC-16 / PROFIBUS (16-bit)
 * Poly: 0x1DCF, Init: 0xFFFF, XorOut: 0xFFFF
 * CRC Table C Source Code & Lookup Table Generator
 */
#include <stdint.h>
#include <stddef.h>

const uint16_t crc_table[256] = {
  0x0000, 0x1DCF, 0x3B9E, 0x2651, 0x773C, 0x6AF3, 0x4CA2, 0x516D, 
  0xEE78, 0xF3B7, 0xD5E6, 0xC829, 0x9944, 0x848B, 0xA2DA, 0xBF15, 
  0xC13F, 0xDCF0, 0xFAA1, 0xE76E, 0xB603, 0xABCC, 0x8D9D, 0x9052, 
  0x2F47, 0x3288, 0x14D9, 0x0916, 0x587B, 0x45B4, 0x63E5, 0x7E2A, 
  0x9FB1, 0x827E, 0xA42F, 0xB9E0, 0xE88D, 0xF542, 0xD313, 0xCEDC, 
  0x71C9, 0x6C06, 0x4A57, 0x5798, 0x06F5, 0x1B3A, 0x3D6B, 0x20A4, 
  0x5E8E, 0x4341, 0x6510, 0x78DF, 0x29B2, 0x347D, 0x122C, 0x0FE3, 
  0xB0F6, 0xAD39, 0x8B68, 0x96A7, 0xC7CA, 0xDA05, 0xFC54, 0xE19B, 
  0x22AD, 0x3F62, 0x1933, 0x04FC, 0x5591, 0x485E, 0x6E0F, 0x73C0, 
  0xCCD5, 0xD11A, 0xF74B, 0xEA84, 0xBBE9, 0xA626, 0x8077, 0x9DB8, 
  0xE392, 0xFE5D, 0xD80C, 0xC5C3, 0x94AE, 0x8961, 0xAF30, 0xB2FF, 
  0x0DEA, 0x1025, 0x3674, 0x2BBB, 0x7AD6, 0x6719, 0x4148, 0x5C87, 
  0xBD1C, 0xA0D3, 0x8682, 0x9B4D, 0xCA20, 0xD7EF, 0xF1BE, 0xEC71, 
  0x5364, 0x4EAB, 0x68FA, 0x7535, 0x2458, 0x3997, 0x1FC6, 0x0209, 
  0x7C23, 0x61EC, 0x47BD, 0x5A72, 0x0B1F, 0x16D0, 0x3081, 0x2D4E, 
  0x925B, 0x8F94, 0xA9C5, 0xB40A, 0xE567, 0xF8A8, 0xDEF9, 0xC336, 
  0x455A, 0x5895, 0x7EC4, 0x630B, 0x3266, 0x2FA9, 0x09F8, 0x1437, 
  0xAB22, 0xB6ED, 0x90BC, 0x8D73, 0xDC1E, 0xC1D1, 0xE780, 0xFA4F, 
  0x8465, 0x99AA, 0xBFFB, 0xA234, 0xF359, 0xEE96, 0xC8C7, 0xD508, 
  0x6A1D, 0x77D2, 0x5183, 0x4C4C, 0x1D21, 0x00EE, 0x26BF, 0x3B70, 
  0xDAEB, 0xC724, 0xE175, 0xFCBA, 0xADD7, 0xB018, 0x9649, 0x8B86, 
  0x3493, 0x295C, 0x0F0D, 0x12C2, 0x43AF, 0x5E60, 0x7831, 0x65FE, 
  0x1BD4, 0x061B, 0x204A, 0x3D85, 0x6CE8, 0x7127, 0x5776, 0x4AB9, 
  0xF5AC, 0xE863, 0xCE32, 0xD3FD, 0x8290, 0x9F5F, 0xB90E, 0xA4C1, 
  0x67F7, 0x7A38, 0x5C69, 0x41A6, 0x10CB, 0x0D04, 0x2B55, 0x369A, 
  0x898F, 0x9440, 0xB211, 0xAFDE, 0xFEB3, 0xE37C, 0xC52D, 0xD8E2, 
  0xA6C8, 0xBB07, 0x9D56, 0x8099, 0xD1F4, 0xCC3B, 0xEA6A, 0xF7A5, 
  0x48B0, 0x557F, 0x732E, 0x6EE1, 0x3F8C, 0x2243, 0x0412, 0x19DD, 
  0xF846, 0xE589, 0xC3D8, 0xDE17, 0x8F7A, 0x92B5, 0xB4E4, 0xA92B, 
  0x163E, 0x0BF1, 0x2DA0, 0x306F, 0x6102, 0x7CCD, 0x5A9C, 0x4753, 
  0x3979, 0x24B6, 0x02E7, 0x1F28, 0x4E45, 0x538A, 0x75DB, 0x6814, 
  0xD701, 0xCACE, 0xEC9F, 0xF150, 0xA03D, 0xBDF2, 0x9BA3, 0x866C
};

uint16_t calculate_crc(const uint8_t *data, size_t length) {
    uint16_t crc = 0xFFFF;
    for (size_t i = 0; i < length; i++) {
        #if 0
        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 ^ 0xFFFF;
}