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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 
19 COMPILER_RT_ABI si_int
__popcountsi2(si_int a)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