unsigned crc16_table[256] = {

    0x0000,0x1189,0x2312,0x329b,0x4624,0x57ad,0x6536,0x74bf,

    0x8c48,0x9dc1,0xaf5a,0xbed3,0xca6c,0xdbe5,0xe97e,0xf8f7,

    0x1891,0x0918,0x3b83,0x2a0a,0x5eb5,0x4f3c,0x7da7,0x6c2e,

    0x94d9,0x8550,0xb7cb,0xa642,0xd2fd,0xc374,0xf1ef,0xe066,

    0x3122,0x20ab,0x1230,0x03b9,0x7706,0x668f,0x5414,0x459d,

    0xbd6a,0xace3,0x9e78,0x8ff1,0xfb4e,0xeac7,0xd85c,0xc9d5,

    0x29b3,0x383a,0x0aa1,0x1b28,0x6f97,0x7e1e,0x4c85,0x5d0c,

    0xa5fb,0xb472,0x86e9,0x9760,0xe3df,0xf256,0xc0cd,0xd144,

    0x6244,0x73cd,0x4156,0x50df,0x2460,0x35e9,0x0772,0x16fb,

    0xee0c,0xff85,0xcd1e,0xdc97,0xa828,0xb9a1,0x8b3a,0x9ab3,

    0x7ad5,0x6b5c,0x59c7,0x484e,0x3cf1,0x2d78,0x1fe3,0x0e6a,

    0xf69d,0xe714,0xd58f,0xc406,0xb0b9,0xa130,0x93ab,0x8222,

    0x5366,0x42ef,0x7074,0x61fd,0x1542,0x04cb,0x3650,0x27d9,

    0xdf2e,0xcea7,0xfc3c,0xedb5,0x990a,0x8883,0xba18,0xab91,

    0x4bf7,0x5a7e,0x68e5,0x796c,0x0dd3,0x1c5a,0x2ec1,0x3f48,

    0xc7bf,0xd636,0xe4ad,0xf524,0x819b,0x9012,0xa289,0xb300,

    0xc488,0xd501,0xe79a,0xf613,0x82ac,0x9325,0xa1be,0xb037,

    0x48c0,0x5949,0x6bd2,0x7a5b,0x0ee4,0x1f6d,0x2df6,0x3c7f,

    0xdc19,0xcd90,0xff0b,0xee82,0x9a3d,0x8bb4,0xb92f,0xa8a6,

    0x5051,0x41d8,0x7343,0x62ca,0x1675,0x07fc,0x3567,0x24ee,

    0xf5aa,0xe423,0xd6b8,0xc731,0xb38e,0xa207,0x909c,0x8115,

    0x79e2,0x686b,0x5af0,0x4b79,0x3fc6,0x2e4f,0x1cd4,0x0d5d,

    0xed3b,0xfcb2,0xce29,0xdfa0,0xab1f,0xba96,0x880d,0x9984,

    0x6173,0x70fa,0x4261,0x53e8,0x2757,0x36de,0x0445,0x15cc,

    0xa6cc,0xb745,0x85de,0x9457,0xe0e8,0xf161,0xc3fa,0xd273,

    0x2a84,0x3b0d,0x0996,0x181f,0x6ca0,0x7d29,0x4fb2,0x5e3b,

    0xbe5d,0xafd4,0x9d4f,0x8cc6,0xf879,0xe9f0,0xdb6b,0xcae2,

    0x3215,0x239c,0x1107,0x008e,0x7431,0x65b8,0x5723,0x46aa,

    0x97ee,0x8667,0xb4fc,0xa575,0xd1ca,0xc043,0xf2d8,0xe351,

    0x1ba6,0x0a2f,0x38b4,0x293d,0x5d82,0x4c0b,0x7e90,0x6f19,

    0x8f7f,0x9ef6,0xac6d,0xbde4,0xc95b,0xd8d2,0xea49,0xfbc0,

    0x0337,0x12be,0x2025,0x31ac,0x4513,0x549a,0x6601,0x7788

};


/* compute 16 bit CCITT crc using the table */

unsigned crc16(unsigned crc,unsigned b)

{

    unsigned ret = crc16_table[(b ^ crc) & 0xff] ^ (crc >> 8);

    return ret;

}