mod6.c

uint32_t mod6(uint32_t x){
    uint32_t y,t;
    t=x&1;
    x>>=1;

    y  = x&0xFFFF;
    x ^= y;
    x>>= 16;
    x += y;
    x += (x>>16);
    x &= 0xFFFF;

    y  = x&0xFF;
    x ^= y;
    x>>= 8;
    x += y;
    x += (x>>8);
    x &= 0xFF;

    y  = x&0xF;
    x ^= y;
    x>>= 4;
    x += y;
    x += (x>>4);
    x &= 0xF;

    y  = x&0x3;
    x ^= y;
    x>>= 2;
    x += y;
    x += (x>>2);
    x &= 0x3;

    y  = x+1;
    y &= 4;
    x += x + t;
    x -= (y + (y>>1));

    return x;


}