1276789Sdim/* ===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===
2276789Sdim *
3276789Sdim *                     The LLVM Compiler Infrastructure
4276789Sdim *
5276789Sdim * This file is dual licensed under the MIT and the University of Illinois Open
6276789Sdim * Source Licenses. See LICENSE.TXT for details.
7276789Sdim *
8276789Sdim * ===----------------------------------------------------------------------===
9276789Sdim *
10276789Sdim * This file implements __popcountsi2 for the compiler_rt library.
11276789Sdim *
12276789Sdim * ===----------------------------------------------------------------------===
13276789Sdim */
14276789Sdim
15276789Sdim#include "int_lib.h"
16276789Sdim
17276789Sdim/* Returns: count of 1 bits */
18276789Sdim
19276789SdimCOMPILER_RT_ABI si_int
20276789Sdim__popcountsi2(si_int a)
21276789Sdim{
22276789Sdim    su_int x = (su_int)a;
23276789Sdim    x = x - ((x >> 1) & 0x55555555);
24276789Sdim    /* Every 2 bits holds the sum of every pair of bits */
25276789Sdim    x = ((x >> 2) & 0x33333333) + (x & 0x33333333);
26276789Sdim    /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) */
27276789Sdim    x = (x + (x >> 4)) & 0x0F0F0F0F;
28276789Sdim    /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) */
29276789Sdim    x = (x + (x >> 16));
30276789Sdim    /* The lower 16 bits hold two 8 bit sums (5 significant bits).*/
31276789Sdim    /*    Upper 16 bits are garbage */
32276789Sdim    return (x + (x >> 8)) & 0x0000003F;  /* (6 significant bits) */
33276789Sdim}
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