BIOS protection by Holly

[megavolt85]

Занимательная математика

Код:

#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>

int main( int argc, char *argv[] )
{
    FILE *fp;
    int i,n=0,size;
    char *buf = malloc(2*1024*1024);
    uint64_t crc, tmp, tmp2, tmp3, sum=0, sum2=0;
    
    fp = fopen(argv[1],"rb");
    
    if(!fp)
    {
        printf("can't open %s\n",argv[1]);
        return 0;
    }
    
    fseek(fp, 0, SEEK_END);
    size = ftell(fp);
    fseek(fp, 0, SEEK_SET);
    
    fread(buf,size,1,fp);
    
    fclose(fp);
    
    for(i=0;i<size;i+=8)
    {
        memcpy(&tmp, &buf[i],4);
        memcpy(&tmp2, &buf[i+4],4);
        
        tmp3 = tmp-tmp2;
        
        if(crc + tmp3 >= 0xffffffff)
        {
            crc = ((crc + tmp3) >> 32);
            n++;
        }
        else
            crc += tmp3;
        
        if(sum + tmp >= 0xffffffff)
        {
            sum = ((sum + tmp) >> 32);
        }
        else
            sum += tmp;
        
        if(sum2 + tmp2 >= 0xffffffff)
        {
            sum2 = ((sum2 + tmp2) >> 32);
        }
        else
            sum2 += tmp2;
    }
    
    printf("KS =  %08X\n",(uint32_t)(crc&0xffffffff));
    printf("N = %d\t%08X\n",n,n);
    printf("SUM1 = %08X\n",(uint32_t)sum);
    printf("SUM2 = %08X\n",(uint32_t)sum2);
    
    return 0;
}

Код:

megavolt@megavolt-GA-790XTA-UD4:~/dreamcast/crc$ ./test 1_01d_01.bios
KS =  A49ED5DB
N = 88922    00015B5A
SUM1 = 796E35CD
SUM2 = 79694A7E
megavolt@megavolt-GA-790XTA-UD4:~/dreamcast/crc$ ./test 1_01d_02.bios
KS =  A49ED5DB
N = 88956    00015B7C
SUM1 = 796E35CD
SUM2 = 79694A7E
megavolt@megavolt-GA-790XTA-UD4:~/dreamcast/crc$ ./test 1_011_01.bios
KS =  71E0CBF9
N = 89624    00015E18
SUM1 = 185C35CD
SUM2 = 4B155460
megavolt@megavolt-GA-790XTA-UD4:~/dreamcast/crc$ ./test Link83_bios_1.0.bios
KS =  71E0CBF9
N = 89599    00015DFF
SUM1 = 185C35CD
SUM2 = 4B155460