Pandigital hex product finder

#include <stdio.h>

int main(void)
{
    unsigned char q[9]; q[9]=3;
    unsigned long long X = 0;
    unsigned long long *y = (unsigned long long*)q;

    unsigned long long Z0,Z1;
    unsigned long long N0 = 0xfedcba9876543210;
    unsigned long long C = 0xf8f7f6f5f4f3f2f1;

    unsigned long long M0[16], M1[16];
    for (int i=0; i<16; i++)
    {
        M0[i] = (1ULL<<(4*i))-1;
        unsigned long long t = ~M0[i];
        M1[i] = t & (t<<4);
    }

    // prepare the 40320 entries for the second table
    unsigned int* p2 = new unsigned int[40320];
    p2[0]=0x76543210;

    for (int i=0; i<8; i++) q[i]=0;
    int ix = 1;
    while (ix!=40320)
    {
        q[0]++;
        int j = 0 ;
        while (q[j]==(8-j)) { q[j]=0; q[j+1]++; j++; }
        unsigned long long N = 0x76543210;
        unsigned long long Z0 = 0;
        for (int j=0; j<8; j++)
        {
            Z0 |= ((N>>(4*q[j]))&0xf)<<(4*j);
            N = (N & M0[q[j]]) | ((N & M1[q[j]])>>4);
        }
        p2[ix]=Z0; ix++;
    }

    for (int i=0; i<8; i++) q[i]=0;
    while (q[7]!=8)
    {
        q[0]++;
        int j = 0;
        while (q[j]==(16-j)) { q[j]=0; q[j+1]++; j++; }
        unsigned long long N = N0;
        Z0 = (N>>(4*q[0]))&0xf;
        N = (N & M0[q[0]]) | ((N & M1[q[0]])>>4);
        for (int j=1; j<8; j++)
        {
            //            printf("pre-%d  %16llx %16llx\n", j, Z0, N);
            Z0 |= ((N>>(4*q[j]))&0xf)<<(4*j);
            N = (N & M0[q[j]]) | ((N & M1[q[j]])>>4);
        }
        // now we have the left-hand number in Z0
        // for the right-hand number we do something similar
        for (int u=0; u<40320; u++)
        {
            Z1 = 0;
            for (int k=0; k<8; k++)
            {
                unsigned int ix = (p2[u]>>(4*k))&0xf;
                unsigned int T = (N>>(4*ix))&0xf;
                unsigned int T1 = T<<(4*k);
                Z1 |= T1;
            }
            if (Z0<Z1)
            {
                unsigned long long prod = Z0*Z1;
                unsigned long long msk = 0;
                for (int k=0; k<16; k++)
                {
                    msk |= 1<<((prod>>(4*k))&0xf);
                }
                if (msk == 0xffff)
                    printf("%llx %llx %llx %llx\n", Z0, Z1, prod, msk);
            }
        }
    }
    printf("%llx\n",X);
}