CRC24Q implementation

[CD1]

I am trying to implement the algorithm of a CRC check, which basically created a value, based on an input message.
So, consider I have a hex message 3F214365876616AB15387D5D59, and I want to obtain the CRC24Q value of the message.
The algorithm that I found to do this is the following:

typedef     unsigned long crc24;
    crc24 crc_check(unsigned char *input) {
        	unsigned char *octets; 
        	crc24 crc = 0xb704ce; // CRC24_INIT;
        	int i;
        	int len = strlen(input); 
    	octets = input;
    
    	while (len--) {
    		crc ^= ((*octets++) << 16); 
    	    
    		for (i = 0; i < 8; i++) {
    			crc <<= 1; 
    			if (crc & 0x1000000) 
    				crc ^= CRC24_POLY;
    		}
    	}
    	return crc & 0xFFFFFF;
    }

where *input=3F214365876616AB15387D5D59.
The problem is that ((*octets++) << 16) will shift by 16 bits the ascii value of the hex character and not the character itself.
So, I made a function to convert the hex numbers to characters.
I know the implementation looks weird, and I wouldn't be surprised if it were wrong.
This is the convert function:

char* convert(unsigned char* message) {
    	unsigned char* input;
    	input = message;
    	int p;
    
    	char *xxxx[20];
    	xxxx[0]="";
    
    	for (p = 0; p < length(message) - 1; p = p + 2) {
    		char* pp[20];
    		pp[0] = input[0];
    		char *c[20];
    		*input++;
    		c[0]= input[0];
    		*input++;
    		strcat(pp,c);
    		char cc;
    		char tt[2];
    		cc = (char ) strtol(pp, &pp, 16);
    		tt[0]=cc;
    		strcat(xxxx,tt);
    
    	}
    	return xxxx;
    }

SO:

unsigned char *msg_hex="3F214365876616AB15387D5D59";
    crc_sum = crc_check(convert((msg_hex)));
    printf("CRC-sum: %x\n", crc_sum);

Thank you very much for any suggestions.

[Schol-R-LEA]

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