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