File content as of revision 0:f016e9e8d48b:

//EDITS
//changed the initial remainder from 0x0000 to 0xffff according to the standards
//made two seperate functions crc16_gen and crc8_gen

#define TOPBIT16 (1 << 15)
#define TOPBIT8 (1 << 7)
#define POLYNOMIAL16 0x1021
#define POLYNOMIAL8 0xEA

typedef uint16_t crctype16; 
crctype16 crc16_gen(const unsigned char message[], unsigned int nBytes){
    crctype16 remainder = 0xffff;
    int byte;
    char bit;
    
    for( byte = 0 ; byte < nBytes ; byte++ ){
        /*
        Bring the data byte by byte
        each time only one byte is brought
        0 xor x = x
        */
        remainder = remainder ^ ( message[byte] << 8 );
        
        for( bit = 8 ; bit > 0 ; bit--){
            /*
            for each bit, xor the remainder with polynomial
            if the MSB is 1
            */
            if(remainder & TOPBIT16){
                remainder = (remainder << 1) ^ POLYNOMIAL16;
                /*
                each time the remainder is xor-ed with polynomial, the MSB is made zero
                hence the first digit of the remainder is ignored in the loop
                */
            }
            else{
                remainder = (remainder << 1);
            }
        }
    }
    
    return remainder;
}

typedef uint8_t crctype8;
crctype8 crc8_gen(const unsigned char message[], unsigned int nBytes){
    
    crctype8 remainder = 0xff;
    
    for(int byte = 0 ; byte < nBytes ; byte++ ){
        /*
        Bring the data byte by byte
        each time only one byte is brought
        0 xor x = x
        */
        remainder = remainder ^ ( message[byte] );
        
        for(int bit = 8 ; bit > 0 ; bit--){
            /*
            for each bit, xor the remainder with polynomial
            if the MSB is 1
            */
            if(remainder & TOPBIT8){
                remainder = (remainder << 1) ^ POLYNOMIAL8;
                /*
                each time the remainder is xor-ed with polynomial, the MSB is made zero
                hence the first digit of the remainder is ignored in the loop
                */
            }
            else{
                remainder = (remainder << 1);
            }
        }
    }
    
    return remainder;
}