#include <stdio.h>
#include <stdlib.h>
#include <vector>

// this program searches for the seed used to generate a given sequence of pseudo random numbers
// as usually generated by HTC bootloaders to fill sdcard headers, or CID blocks
//
typedef std::vector<unsigned char> ByteVector;

#define RNG(seed) ((unsigned char)((seed)>>16))

bool testseed(unsigned long seed, const unsigned char *buf, int size)
{
    while (size--) {
        if (*buf++ != RNG(seed))
            return false;
        seed = 2531011+214013*seed;
    }
    return true;
}
bool dumpseed(unsigned long seed, int size)
{
    printf("  ");
    for (int i=1 ; i<=size ; i++) {
        if ((i&31)==0)
            printf("\n");

        printf("%02x", RNG(seed));
        seed = 2531011+214013*seed;
    }
    printf("\n");
    return true;
}


bool findseed(const unsigned char *buf, int size)
{
    unsigned long seed= 0;
    const unsigned char *p=buf;
    const unsigned char *end= buf+size;

    unsigned char c0= buf[0];

    unsigned long seedhist[256];
    int seedidx=0;

    while (1) {
        seed = 2531011+214013*seed;
        seedhist[seedidx++]= seed;
        if (seedidx==256) seedidx=0;
        if (RNG(seed)==c0) {
            if (testseed(seed, buf, size))
                break;
        }
        if (seed==0)
            return false;
    }
    printf("found seed: %08lx ( -256: %08lx )\n", seed, seedhist[seedidx]);
    dumpseed(seedhist[seedidx], 512);
    return true;
}
int c2nyb(char c)
{
    if (c>='0' && c<='9') return c-'0';
    if (c>='a' && c<='f') return c-'a'+10;
    if (c>='A' && c<='F') return c-'A'+10;
    return -1;
}
int cvhex2bytes(unsigned char *buf, int bufsize, char *hex)
{
    int nyb[2];
    int i=0;
    int nbytes=0;
    while (*hex) {
        nyb[i]= c2nyb(*hex++);
        if (nyb[i]>=0)
            i++;
        if (i>1) {
            *buf++ = (nyb[0]<<4) | nyb[1];
            nbytes++;
            if (nbytes>=bufsize)
                break;
            i=0;
        }
    }
    return nbytes;
}

int main(int argc, char **argv)
{
    ByteVector data;
    int i;

    for (i=1 ; i<argc ; i++)
    {
        int pos= data.size();
        data.resize(data.size()+strlen(argv[i])/2);
        int size= cvhex2bytes(&data[pos], data.size()-pos, argv[i]);

        data.resize(pos+size);
    }
    findseed(&data[0], data.size());
}