#include <stdio.h>

#define MAX_ERRORS  10

int count_bits(unsigned char a){
    int i,bits=0;
    for(i=0; i<8; i++){
        if( ((a>>i) & 0x01) != 0) 
            bits++;
    }
    return bits;
}

int main(int argc,char *argv[]){
    if(argc != 3){
        printf("Usage: %s <file1> <file2>\n",argv[0]);
        return -1;
    }

    long int total_bits = 0;
    long int total_errors = 0;
    
    int diff;
    unsigned char byte1, byte2;

    FILE* f1 = fopen(argv[1], "r");
    FILE* f2 = fopen(argv[2], "r");

    while((fread(&byte1, 1, 1, f1)) != 0){
        if(fread(&byte2, 1, 1, f2) == 0)
            break;

        total_bits += 8;

        if(byte1 == byte2)
            continue;
        
        diff = count_bits(byte1 ^ byte2);
        total_errors += diff;
     
        if(total_errors < MAX_ERRORS){
            printf("%d error[s] in byte %d.\n", diff, total_bits/8);
        } else if(total_errors==MAX_ERRORS){
            printf("too many errors, no longer outputting location...\n");
        }

    }
    
    fclose(f1);
    fclose(f2);

    printf("Total Bits: %lu\n", total_bits);
    printf("Total Errors: %lu\n", total_errors);

    double error_rate = (((double) total_errors) / ((double) total_bits));

    printf("BER: %f\n", error_rate);
}