1/* ===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===
2 *
3 *                     The LLVM Compiler Infrastructure
4 *
5 * This file is dual licensed under the MIT and the University of Illinois Open
6 * Source Licenses. See LICENSE.TXT for details.
7 *
8 * ===----------------------------------------------------------------------===
9 *
10 * This file implements __popcountsi2 for the compiler_rt library.
11 *
12 * ===----------------------------------------------------------------------===
13 */
14
15#include "int_lib.h"
16
17/* Returns: count of 1 bits */
18
19COMPILER_RT_ABI si_int
20__popcountsi2(si_int a)
21{
22    su_int x = (su_int)a;
23    x = x - ((x >> 1) & 0x55555555);
24    /* Every 2 bits holds the sum of every pair of bits */
25    x = ((x >> 2) & 0x33333333) + (x & 0x33333333);
26    /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) */
27    x = (x + (x >> 4)) & 0x0F0F0F0F;
28    /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) */
29    x = (x + (x >> 16));
30    /* The lower 16 bits hold two 8 bit sums (5 significant bits).*/
31    /*    Upper 16 bits are garbage */
32    return (x + (x >> 8)) & 0x0000003F;  /* (6 significant bits) */
33}
34