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typedef unsigned int uint;
uint swapBits(uint x, uint i, uint j) {
    uint lo = ((x >> i) & 1);
    uint hi = ((x >> j) & 1);
    if (lo ^ hi) 
        x ^= ((1U << i) | (1U << j)); // gist, because X ^ 0 = X
    return x;
}

uint reverseXor(uint x) {
    uint n = sizeof(x) * 8;
    for (uint i = 0; i < n/2; i++) 
        x = swapBits(x, i, n-i-1);
    return x;
}