A faster method of computing the number of set bits in the data is by using a lookup table. The following example uses data in a 4-bit lookup table. This requires eight passes to evaluate 32 bits. A larger lookup table reduces the number of passes, but increases the size of the table in memory.

uint32_t bitsArray[] = {
    0, // 0
    1, // 1
    1, // 2
    2, // 3
    1, // 4
    2, // 5
    2, // 6
    3, // 7
    1, // 8
    2, // 9
    2, // 10
    3, // 11
    2, // 12
    3, // 13
    3, // 14
    4, // 15
};
/**
 * Computation of the number of set bits in a 32-bit value by lookup table.
 *
 * \details Counting of the number of bits set in a value using a loop and
 * evaluating each nibble in the lookup table and then right shifting the remaining value by 4.
 *
 * \param    uint32_t in of the value to be computed.
 *
 * \returns  uint32_t numBits of the computation.
 */
uint32_t countBits (uint32_t in)
{
    uint32_t numBits = 0;
    while (in != 0)
    {
        numBits += bitsArray[in & 0x0F];
        in >>= 4;
    }
    return numBits;
}