Algorithms

// NOTE: The order of the bits is inconsequential, as long as each string of 4 bits comes from a different 64-bit block
output = (bit[ 0] << 255) | (bit[ 64] << 254) | (bit[128] << 253) | (bit[192] << 252)
       | (bit[ 1] << 251) | (bit[ 65] << 250) | (bit[129] << 249) | (bit[193] << 248)
       | ...
       | (bit[63] <<   3) | (bit[127] <<   2) | (bit[191] <<   1) | (bit[255])

// Interleave
__uint16 *data   = new __uint16[32 / sizeof(__uint16)]; // Data to interleave
__uint64 *result = new __uint64[32 / sizeof(__uint64)]();

for (int resIdx = 0; resIdx < 4; ++resIdx) {
    for (int dataIdx = resIdx; dataIdx < 16; dataIdx += 4) {
        __uint64 temp = data[dataIdx];
        temp |= temp << 24;
        temp |= temp << 12;
        temp &= 0x000F000F000F000FULL;
        temp |= temp <<  6;
        temp |= temp <<  3;
        temp &= 0x1111111111111111ULL;
        result[resIdx] |= temp << (dataIdx & 3);
    }
}

// Deinterleave
__uint64 *data   = new __uint64[32 / sizeof(__uint64)]; // Data to deinterleave
__uint16 *result = new __uint16[32 / sizeof(__uint16)];
for (int dataIdx = 0; dataIdx < 4; ++dataIdx) {
    for (int resIdx = dataIdx; resIdx < 16; resIdx += 4) {
        __uint64 temp = data[dataIdx] >> (resIdx >> 2);
        temp &= 0x1111111111111111ULL;
        temp |= temp >>  3;
        temp |= temp >>  6;
        temp &= 0x000F000F000F000FULL;
        temp |= temp >> 12;
        temp |= temp >> 24;
        result[resIdx] = (__uint16)temp;
    }
}