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 | |