xorer by xerpi

/* by xerpi */

#include <stdio.h>

#define min(num1, num2) (num1<num2 ? num1 : num2)
#define BUF_SIZE 1

int file_size(FILE *file);
void xorer( FILE *input1,  FILE *input2,  FILE *output);

int main(int argc, char **argv){

    if( argc < 3 ){
        printf("Too low arguments.\nUse: xorer <file1> <file2> (<output>)");
        return -1;
    }

    FILE *input1;
    FILE *input2;
    FILE *output;
    char *output_filename;
    //Check if the 4th argument exists, if it exists, it'll be the name of the output file
        if( argc >= 4)
            output_filename = argv[3];
        else
            output_filename = "xored";
    //Open the files
        input1 =  fopen (argv[1], "r");
            if(!input1){
                printf("File %s could not be opened.", argv[1]);
                return -1;
            }
        input2 =  fopen (argv[2], "r");
            if(!input2){
                printf("File %s could not be opened.", argv[2]);
                return -1;
            }
        output =  fopen (output_filename, "w+");
    //Xor the files
        xorer(input1, input2, output);
    //Close the files
        fclose(input1);
        fclose(input2);
        fflush(output);
        fclose(output);
    return 0;
}


int file_size(FILE *file){
    fseek(file, 0, SEEK_END);
    return ftell(file);
}

void xorer( FILE *input1,  FILE *input2,  FILE *output){
    int i, min_size, size1, size2;
    unsigned char buffer, data1, data2;
     //Check the file size
        size1 = file_size(input1);
        size2 = file_size(input2);
     //Set the cursor at the begin of the files
        fseek(input1, 0, SEEK_SET);
        fseek(input2, 0, SEEK_SET);
            min_size = min(size1, size2);
            printf("Size file 1: %i\nSize file 2: %i\nOutput file size: %i", size1, size2, min_size);
    //Xor algorithm
        for(i = 0; i< min_size; i++){
            fread(&data1, 1, BUF_SIZE, input1);
            fread(&data2, 1, BUF_SIZE, input2);
            buffer = data1 ^ data2;
            fwrite(&buffer, 1, BUF_SIZE, output);
        }
    return;
}