1214152Sed/* ===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===
2214152Sed *
3214152Sed *                     The LLVM Compiler Infrastructure
4214152Sed *
5222656Sed * This file is dual licensed under the MIT and the University of Illinois Open
6222656Sed * Source Licenses. See LICENSE.TXT for details.
7214152Sed *
8214152Sed * ===----------------------------------------------------------------------===
9214152Sed *
10214152Sed * This file implements __popcountsi2 for the compiler_rt library.
11214152Sed *
12214152Sed * ===----------------------------------------------------------------------===
13214152Sed */
14214152Sed
15214152Sed#include "int_lib.h"
16214152Sed
17214152Sed/* Returns: count of 1 bits */
18214152Sed
19222656SedCOMPILER_RT_ABI si_int
20214152Sed__popcountsi2(si_int a)
21214152Sed{
22214152Sed    su_int x = (su_int)a;
23214152Sed    x = x - ((x >> 1) & 0x55555555);
24214152Sed    /* Every 2 bits holds the sum of every pair of bits */
25214152Sed    x = ((x >> 2) & 0x33333333) + (x & 0x33333333);
26214152Sed    /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) */
27214152Sed    x = (x + (x >> 4)) & 0x0F0F0F0F;
28214152Sed    /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) */
29214152Sed    x = (x + (x >> 16));
30214152Sed    /* The lower 16 bits hold two 8 bit sums (5 significant bits).*/
31214152Sed    /*    Upper 16 bits are garbage */
32214152Sed    return (x + (x >> 8)) & 0x0000003F;  /* (6 significant bits) */
33214152Sed}
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