| 1 | /* $NetBSD: popcount32.c,v 1.5 2015/05/29 19:39:41 matt 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 1.5 2015/05/29 19:39:41 matt 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 | |
| 56 | unsigned int |
| 57 | popcount32(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 | |