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 /* 47 * This a hybrid algorithm for bit counting between parallel counting and 48 * using multiplication. The idea is to sum up the bits in each Byte, so 49 * that the final accumulation can be done with a single multiplication. 50 * If the platform has a slow multiplication instruction, it can be replaced 51 * by the commented out version below. 52 */ 53 54 unsigned int 55 popcount32(uint32_t v) 56 { 57 unsigned int c; 58 59 v = v - ((v >> 1) & 0x55555555U); 60 v = (v & 0x33333333U) + ((v >> 2) & 0x33333333U); 61 v = (v + (v >> 4)) & 0x0f0f0f0fU; 62 c = (v * 0x01010101U) >> 24; 63 /* 64 * v = (v >> 16) + v; 65 * v = (v >> 8) + v; 66 * c = v & 255; 67 */ 68 69 return c; 70 } 71 72 #if UINT_MAX == 0xffffffffU 73 __strong_alias(popcount, popcount32) 74 #endif 75 76 #if ULONG_MAX == 0xffffffffU 77 __strong_alias(popcountl, popcount32) 78 #endif 79