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
19COMPILER_RT_ABI si_int
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