Interview Question for Senior Software Engineer at QUALCOMM:

static const int NumberOfSetBits[8] = { /* in nibble, half byte */
  0, /* 0x0, b0000 */
  1, /* 0x1, b0001 */
  1, /* 0x2, b0010 */
  2, /* 0x3, b0011 */
  1, /* 0x4, b0100 */
  2, /* 0x5, b0101 */
  2, /* 0x6, b0110 */
  3 /* 0x7, b0111 */
  1 /* 0x8, b1000 */
  2 /* 0x9, b1001 */
  2 /* 0xA, b1010 */
  3 /* 0xB, b1011 */
  2 /* 0xC, b1100 */
  3 /* 0xD, b1101 */
  3 /* 0xE, b1110 */
  4 /* 0xF, b1111 */
};

#define NumBytesInInt 4 /* assumes 32bit system */

int GetNumberOfSetBits(int anInteger)
{

    uint8_t buf[NumBytesInInt ];
    int i;
    int count = 0;

    memcpy(buf, &anInteger, sizeof(buf));
    for (i=0; i<NumBytesInInt; ++i) {
        count += NumberOfSetBits[buf[i] &0x0F];
        count += NumberOfSetBits[buf[i] >> 4];
    }

    return count;
}