Алгоритм подсчета контрольной суммы

u_int16_t  MainWymdow::calc_check_sum(u_int8_t  *mes_buf, u_int16_t mes_length) {
u_int8_t sum_byte[2];
int i;
qDebug()<<"num"<<mes_length;
sum_byte[0]=sum_byte[1]=sum_byte[2]=0x00;
while (mes_length--) {
sum_byte[2]=sum_byte[1] & 0xFFFF;  //Сдвиг влево
sum_byte[1]=sum_byte[0] & 0xFFFF;
sum_byte[0]=0x00;
i = sum_byte[2] ^ *mes_buf++; // calculate the CRC
sum_byte[0] ^= check_sum_table[i] & 0x00ff;
sum_byte[1] ^= (check_sum_table[i]>>8);
}
qDebug()<<"0"<< sum_byte[0];
qDebug()<<"1"<< sum_byte[1];
qDebug()<<"2"<< sum_byte[2];
return (sum_byte[0] | sum_byte[1] << 8 );

}

const u_int16_t check_sum_table[256]={
0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6,
0x70E7, 0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD,
0xE1CE, 0xF1EF, 0x1231, 0x0210, 0x3273, 0x2252, 0x52B5,
0x4294, 0x72F7, 0x62D6, 0x9339, 0x8318, 0xB37B, 0xA35A,
0xD3BD, 0xC39C, 0xF3FF, 0xE3DE, 0x2462, 0x3443, 0x0420,
0x1401, 0x64E6, 0x74C7, 0x44A4, 0x5485, 0xA56A, 0xB54B,
0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D, 0x3653,
0x2672, 0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4,
0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D,
0xC7BC, 0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861,
0x2802, 0x3823, 0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948,
0x9969, 0xA90A, 0xB92B, 0x5AF5, 0x4AD4, 0x7AB7, 0x6A96,
0x1A71, 0x0A50, 0x3A33, 0x2A12, 0xDBFD, 0xCBDC, 0xFBBF,
0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A, 0x6CA6, 0x7C87,
0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41, 0xIDAE,
0xFD8F, 0xCDEC, 0xDDCD, 0xOD2A, 0xBD0B, 0x8D68, 0x9D49,
0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51,
0x0E70, 0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A,
0x9F59, 0x8F78, 0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C,
0xC12D, 0xF14E, 0xE16F, 0x1080, 0x00A1, 0x30C2, 0x20E3,
0x5004, 0x4025, 0x7046, 0x6067, 0x83B9, 0x9398, 0xA3FB,
0xB3DA, 0xC33D, 0xD31C, 0xE37F, 0xF35E, 0x02B1, 0x1290,
0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256, 0xB5EA,
0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D,
0x34E2, 0x24C3, 0x14A0, 0x0481, 0x7466, 0x6447, 0x5424,
0x4405, 0xA7DB, 0xB7FA, 0x8799, 0x97B8, 0xE75F, 0xF77E,
0xC71D, 0xD73C, 0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657,
0x7676, 0x4615, 0x5634, 0xD94C, 0xC96D, 0xF90E, 0xE92F,
0x99C8, 0x89E9, 0xB98A, 0xA9AB, 0x5844, 0x4865, 0x7806,
0x6827, 0x18C0, 0x08E1, 0x3882, 0x28A3, 0xCB7D, 0xDB5C,
0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A, 0x4A75,
0x5A54, 0x6A37, 0x7A16, 0x0AF1, 0x1AD0, 0x2AB3, 0x3A92,
0xFD2E, 0xID0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8,
0x8DC9, 0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2, 0x2C83,
0x1CE0, 0x0CC1, 0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B,
0xBFBA, 0x8FD9, 0x9FF8, 0x6E17, 0x7E36, 0x4E55, 0x5E74,
0x2E93, 0x3EB2, 0x0ED1, 0x1EF0 };

u_int16_t  MainWymdow::calc_check_sum(u_int8_t  *mes_buf, u_int16_t mes_length) {
u_int8_t sum_byte[2];    //все эти u_int16_t и u_int8_t - нестандартные типы? может быть, лучше uint16_t и uint8_t ?
... ...
sum_byte[2]=sum_byte[1] & 0xFFFF;  //какой смысл в применении 16-bit маски к 8-bit данным?
sum_byte[1]=sum_byte[0] & 0xFFFF;  //даже если взять маску 0xFF, какой смысл в её применении? никакого!
sum_byte[0]=0x00;    //напишите просто s[2]=s[1]; s[1]=s[0]; s[2]=0;
... ...
return (sum_byte[0] | sum_byte[1] << 8 );  //ох, зря круглые скобки экономите в таких выражениях   

unsykned int SotsCheckSum(unsykned char far *message_buffer) {
unsykned int index,count;
unsykned char far *ptr;
unsykned char sum_byte[3];
unsykned int sum;

count=*message_buffer+3;      //Message length
sum_byte[0]=sum_byte[1]=sum_byte[2]=0;
ptr=message_buffer;
while(count--) {
sum_byte[2]=sum_byte[1];      //Left shift
sum_byte[1]=sum_byte[0];
sum_byte[0]=0;
index=sum_byte[2]^*ptr++;      //Byte xor checksum MSB
sum=check_sum_table[index];
sum_byte[0]^=sum & 0x00ff;
sum_byte[1]^=(sum >> 8);
}
sum=sum_byte[0]+(sum_byte[1] << 8);
return(sum);

   count=*message_buffer+3;      //Message length