Passing a pointer to a function

[digidig]

Hi,

I'm coding a hash algorithm (SHA-1) in C. The algorithm works, everything compiles and I seem to be getting the correct results when I simulate it. I obviously want to automate the checking proceedure so have obtained the necessary results from "hashcalc" and included them as several 20 by 8bit arrays within my code. The hash calc algorithm returns a 5 by 32bit array to an 8bit pointer, I'm then storing the data to a 20 by 8bit array using a do-while loop before passing pointers to this array along with the array containing the known results to another function which compairs the 2 arrays as can be seen in the below code:

void main (void)
{
    uint8_T sha1_check   = 0;
    uint8_T *sha1_op_ptr = 0;
    uint8_T expected_sha1_result_1[20] = {0x3e,0x51,0x75,0x38,0x6b,0xe6,0x83,0xd2,0xf2,0x3,
0xf3,0xfa,0x3e,0xab,0x89,0x2a,0x79,0x90,0x82,0xf7}; /*data obtained from hash checker*/
 
 
    sha1_op_ptr = (uint8_T *)calculateSHA1();
 
    do{
        res[loop] = *sha1_op_ptr++;
    }while(loop++ < 20);
 
    sha1_check = checkOutputSHA1((uint8_T *)&res[0],(uint8_T *)&expected_sha1_result[0]);
}
 
uint32_T calculateSHA1(void)
{
    uint32_T hash_arr[5] = {0};
 
    /* Perform Hash Algorithm */
 
    return hash_arr;
}
 
void checkOutputSHA1(uint8_T *hash_res_ptr,uint8_T *result_from_hash_checker_ptr);
{
    uint8_T matched_byte = 0;
    uint8_T check_sha1_res_loop = 0;
    uint8_T res[20] = 0;
 
 
    do{
        res[check_sha1_res_loop]= *hash_res_ptr;
        if(*hash_res_ptr++ == *result_from_hash_checker_ptr++)
        {
            matched_byte++;
        }
    }while(check_sha1_res_loop++ < 20);    
 
    return matched_byte;
}
 

Now this works as matched_byte returns 20. However this approach is requiring me to carry out 2 do-while loops. 1 in main and 1 in checkOutputSHA1() which seems a bit pointless when I believe I could get away with just performing a do-while in checkOutputSHA1() if I passed sha1_op_ptr to checkOutputSHA1() instead of res[] as such..

void main (void)
{
    uint8_T sha1_check   = 0;
 
    uint8_T *sha1_op_ptr = 0;
 
    /*data obtained from hash checker*/
    uint8_T expected_sha1_result_1[20] = {0x3e,0x51,0x75,0x38,0x6b,0xe6,0x83,0xd2,0xf2,0x31,
                                         0xf3,0xfa,0x3e,0xab,0x89,0x2a,0x79,0x90,0x82,0xf7}; 
 
 
    sha1_op_ptr = (uint8_T *)calculateSHA1();
 
    do{
        res[loop] = *sha1_op_ptr++;
    }while(loop++ < 20);
 
    sha1_check = checkOutputSHA1(sha1_op_ptr,(uint8_T *)&expected_sha1_result[0]);
}
 

Unfortunately this doesn't seem to work correctly as matched_byte = 0. Any suggestions as to what I'm doing wrong would be greatly appreciated as it's driving me nuts!!! Does the function prototype for checkOutputSHA() need modifying as I've left it the same or am I just trying to achieve the impossible?

Cheers.

[ravenspoint]

It looks to me that in line 18 you are passing the incremented pointer ( incremented at 15 ). Why do you not remove lines 14 to 16, since this was the point anyway?

[ravenspoint]

Another problem. In calculateSHA1() you are returning a pointer to an automatic, which will 'go away' at some point.

[digidig]

It looks to me that in line 18 you are passing the incremented pointer ( incremented at 15 ). Why do you not remove lines 14 to 16, since this was the point anyway?

opps, in my actual code I had, this was a cut and paste jobby from the previous code snippet and got left in. careless

[digidig]

Another problem. In calculateSHA1() you are returning a pointer to an automatic, which will 'go away' at some point.

So I am and indeed it does. Spotters badge for ravenspoint, problem solved :O)