1 /* ===-- popcountdi2.c - Implement __popcountdi2 ----------------------------===
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 __popcountdi2 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
__popcountdi2(di_int a)20 __popcountdi2(di_int a)
21 {
22     du_int x2 = (du_int)a;
23     x2 = x2 - ((x2 >> 1) & 0x5555555555555555uLL);
24     /* Every 2 bits holds the sum of every pair of bits (32) */
25     x2 = ((x2 >> 2) & 0x3333333333333333uLL) + (x2 & 0x3333333333333333uLL);
26     /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (16) */
27     x2 = (x2 + (x2 >> 4)) & 0x0F0F0F0F0F0F0F0FuLL;
28     /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (8) */
29     su_int x = (su_int)(x2 + (x2 >> 32));
30     /* The lower 32 bits hold four 16 bit sums (5 significant bits). */
31     /*   Upper 32 bits are garbage */
32     x = x + (x >> 16);
33     /* The lower 16 bits hold two 32 bit sums (6 significant bits). */
34     /*   Upper 16 bits are garbage */
35     return (x + (x >> 8)) & 0x0000007F;  /* (7 significant bits) */
36 }
37