+ unsigned short i, v, tcrc = 0;
+
+ v = (crc ^ c) & 0xff;
+ for (i = 0; i < 8; i++) {
+ tcrc = ( (tcrc ^ v) & 1 ) ? ( tcrc >> 1 ) ^ 0x8408 : tcrc >> 1;
+ v >>= 1;
+ }
+
+ return ((crc >> 8) ^ tcrc)&0xffff;
+}
+
+uint16_t crc16(uint8_t const *message, int length, uint16_t remainder, uint16_t polynomial) {
+
+ if (length == 0) return (~remainder);
+
+ for (int byte = 0; byte < length; ++byte) {
+ remainder ^= (message[byte] << 8);
+ for (uint8_t bit = 8; bit > 0; --bit) {
+ if (remainder & 0x8000) {
+ remainder = (remainder << 1) ^ polynomial;
+ } else {
+ remainder = (remainder << 1);
+ }
+ }
+ }
+ return remainder;
+}
+
+uint16_t crc16_ccitt(uint8_t const *message, int length) {
+ return crc16(message, length, 0xffff, 0x1021);
+}
+
+uint16_t crc16_ccitt_kermit(uint8_t const *message, int length) {
+ return bit_reverse_uint16(crc16(message, length, 0x0000, 0x1021));
+}
+
+uint16_t bit_reverse_uint16 (uint16_t value) {
+ const uint16_t mask0 = 0x5555;
+ const uint16_t mask1 = 0x3333;
+ const uint16_t mask2 = 0x0F0F;
+ const uint16_t mask3 = 0x00FF;