1/* $NetBSD: popcount32.c,v 1.4 2011/08/21 21:25:04 dholland Exp $ */ 2/*- 3 * Copyright (c) 2009 The NetBSD Foundation, Inc. 4 * All rights reserved. 5 * 6 * This code is derived from software contributed to The NetBSD Foundation 7 * by Joerg Sonnenberger. 8 * 9 * Redistribution and use in source and binary forms, with or without 10 * modification, are permitted provided that the following conditions 11 * are met: 12 * 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in 17 * the documentation and/or other materials provided with the 18 * distribution. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 21 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 22 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 23 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 24 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 25 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING, 26 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 27 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 28 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 29 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 30 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 */ 33 34#include <sys/cdefs.h> 35__RCSID("$NetBSD: popcount32.c,v 1.4 2011/08/21 21:25:04 dholland Exp $"); 36 37#if !defined(_KERNEL) && !defined(_STANDALONE) 38#include <limits.h> 39#include <stdint.h> 40#include <strings.h> 41#else 42#include <lib/libkern/libkern.h> 43#include <machine/limits.h> 44#endif 45 46#ifndef popcount32 // might be a builtin 47 48/* 49 * This a hybrid algorithm for bit counting between parallel counting and 50 * using multiplication. The idea is to sum up the bits in each Byte, so 51 * that the final accumulation can be done with a single multiplication. 52 * If the platform has a slow multiplication instruction, it can be replaced 53 * by the commented out version below. 54 */ 55 56unsigned int 57popcount32(uint32_t v) 58{ 59 unsigned int c; 60 61 v = v - ((v >> 1) & 0x55555555U); 62 v = (v & 0x33333333U) + ((v >> 2) & 0x33333333U); 63 v = (v + (v >> 4)) & 0x0f0f0f0fU; 64 c = (v * 0x01010101U) >> 24; 65 /* 66 * v = (v >> 16) + v; 67 * v = (v >> 8) + v; 68 * c = v & 255; 69 */ 70 71 return c; 72} 73 74#if UINT_MAX == 0xffffffffU 75__strong_alias(popcount, popcount32) 76#endif 77 78#if ULONG_MAX == 0xffffffffU 79__strong_alias(popcountl, popcount32) 80#endif 81 82#endif /* !popcount32 */ 83