1*b3de343eSJohn Chung /* SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later */
2*b3de343eSJohn Chung
3*b3de343eSJohn Chung #include "crc-16-ccitt.h"
4*b3de343eSJohn Chung
5*b3de343eSJohn Chung /*
6*b3de343eSJohn Chung * Implementation detail and FCS lookup table is based
7*b3de343eSJohn Chung * on https://www.ietf.org/rfc/rfc1662.txt Appendix C.
8*b3de343eSJohn Chung *
9*b3de343eSJohn Chung * FCS lookup table as calculated by the table generator.
10*b3de343eSJohn Chung */
11*b3de343eSJohn Chung static const uint16_t crc_16_ccitt_table[256] = {
12*b3de343eSJohn Chung 0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf, 0x8c48,
13*b3de343eSJohn Chung 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7, 0x1081, 0x0108,
14*b3de343eSJohn Chung 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e, 0x9cc9, 0x8d40, 0xbfdb,
15*b3de343eSJohn Chung 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876, 0x2102, 0x308b, 0x0210, 0x1399,
16*b3de343eSJohn Chung 0x6726, 0x76af, 0x4434, 0x55bd, 0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e,
17*b3de343eSJohn Chung 0xfae7, 0xc87c, 0xd9f5, 0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e,
18*b3de343eSJohn Chung 0x54b5, 0x453c, 0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd,
19*b3de343eSJohn Chung 0xc974, 0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
20*b3de343eSJohn Chung 0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3, 0x5285,
21*b3de343eSJohn Chung 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a, 0xdecd, 0xcf44,
22*b3de343eSJohn Chung 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72, 0x6306, 0x728f, 0x4014,
23*b3de343eSJohn Chung 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9, 0xef4e, 0xfec7, 0xcc5c, 0xddd5,
24*b3de343eSJohn Chung 0xa96a, 0xb8e3, 0x8a78, 0x9bf1, 0x7387, 0x620e, 0x5095, 0x411c, 0x35a3,
25*b3de343eSJohn Chung 0x242a, 0x16b1, 0x0738, 0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862,
26*b3de343eSJohn Chung 0x9af9, 0x8b70, 0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e,
27*b3de343eSJohn Chung 0xf0b7, 0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
28*b3de343eSJohn Chung 0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036, 0x18c1,
29*b3de343eSJohn Chung 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e, 0xa50a, 0xb483,
30*b3de343eSJohn Chung 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5, 0x2942, 0x38cb, 0x0a50,
31*b3de343eSJohn Chung 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd, 0xb58b, 0xa402, 0x9699, 0x8710,
32*b3de343eSJohn Chung 0xf3af, 0xe226, 0xd0bd, 0xc134, 0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7,
33*b3de343eSJohn Chung 0x6e6e, 0x5cf5, 0x4d7c, 0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1,
34*b3de343eSJohn Chung 0xa33a, 0xb2b3, 0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72,
35*b3de343eSJohn Chung 0x3efb, 0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
36*b3de343eSJohn Chung 0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a, 0xe70e,
37*b3de343eSJohn Chung 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1, 0x6b46, 0x7acf,
38*b3de343eSJohn Chung 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9, 0xf78f, 0xe606, 0xd49d,
39*b3de343eSJohn Chung 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330, 0x7bc7, 0x6a4e, 0x58d5, 0x495c,
40*b3de343eSJohn Chung 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
41*b3de343eSJohn Chung };
42*b3de343eSJohn Chung
43*b3de343eSJohn Chung /*
44*b3de343eSJohn Chung * Calculate a new fcs given the current fcs and the new data.
45*b3de343eSJohn Chung */
crc_16_ccitt(uint16_t fcs,const uint8_t * cp,uint32_t len)46*b3de343eSJohn Chung uint16_t crc_16_ccitt(uint16_t fcs, const uint8_t *cp, uint32_t len)
47*b3de343eSJohn Chung {
48*b3de343eSJohn Chung while (len--)
49*b3de343eSJohn Chung fcs = crc_16_ccitt_byte(fcs, *cp++);
50*b3de343eSJohn Chung
51*b3de343eSJohn Chung return fcs;
52*b3de343eSJohn Chung }
53*b3de343eSJohn Chung
crc_16_ccitt_byte(uint16_t fcs,const uint8_t c)54*b3de343eSJohn Chung uint16_t crc_16_ccitt_byte(uint16_t fcs, const uint8_t c)
55*b3de343eSJohn Chung {
56*b3de343eSJohn Chung return (fcs >> 8) ^ crc_16_ccitt_table[(fcs ^ c) & 0xff];
57*b3de343eSJohn Chung }
58