78 lines
2.6 KiB
C
78 lines
2.6 KiB
C
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/* $NetBSD: popcount32.c,v 1.3 2009/07/21 19:56:55 drochner Exp $ */
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/*-
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* Copyright (c) 2009 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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* by Joerg Sonnenberger.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__RCSID("$NetBSD: popcount32.c,v 1.3 2009/07/21 19:56:55 drochner Exp $");
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#if !defined(_KERNEL) && !defined(_STANDALONE)
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#include <limits.h>
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#include <strings.h>
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#else
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#include <lib/libkern/libkern.h>
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#include <machine/limits.h>
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#endif
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/*
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* This a hybrid algorithm for bit counting between parallel counting and
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* using multiplication. The idea is to sum up the bits in each Byte, so
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* that the final accumulation can be done with a single multiplication.
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* If the platform has a slow multiplication instruction, it can be replaced
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* by the commented out version below.
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*/
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unsigned int
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popcount32(uint32_t v)
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{
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unsigned int c;
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v = v - ((v >> 1) & 0x55555555U);
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v = (v & 0x33333333U) + ((v >> 2) & 0x33333333U);
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v = (v + (v >> 4)) & 0x0f0f0f0fU;
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c = (v * 0x01010101U) >> 24;
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/*
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* v = (v >> 16) + v;
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* v = (v >> 8) + v;
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* c = v & 255;
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*/
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return c;
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}
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#if UINT_MAX == 0xffffffffU
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__strong_alias(popcount, popcount32)
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#endif
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#if ULONG_MAX == 0xffffffffU
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__strong_alias(popcountl, popcount32)
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#endif
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