/* $NetBSD: popcount32.c,v 1.5 2015/05/29 19:39:41 matt Exp $ */
/*-
* Copyright (c) 2009 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Joerg Sonnenberger.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <sys/cdefs.h>
__RCSID("$NetBSD: popcount32.c,v 1.5 2015/05/29 19:39:41 matt Exp $");
/*
* This a hybrid algorithm for bit counting between parallel counting and
* using multiplication. The idea is to sum up the bits in each Byte, so
* that the final accumulation can be done with a single multiplication.
* If the platform has a slow multiplication instruction, it can be replaced
* by the commented out version below.
*/
unsigned int
popcount32(uint32_t v)
{
unsigned int c;
v = v - ((v >> 1) & 0x55555555U);
v = (v & 0x33333333U) + ((v >> 2) & 0x33333333U);
v = (v + (v >> 4)) & 0x0f0f0f0fU;
c = (v * 0x01010101U) >> 24;
/*
* v = (v >> 16) + v;
* v = (v >> 8) + v;
* c = v & 255;
*/
