haiku/headers/private/kernel/util/BitUtils.h

/*
 * Copyright 2013 Haiku, Inc. All rights reserved.
 * Distributed under the terms of the MIT License.
 *
 * Authors:
 *		Paweł Dziepak, pdziepak@quarnos.org
 */
#ifndef KERNEL_UTIL_BITUTIL_H
#define KERNEL_UTIL_BITUTIL_H


#include <SupportDefs.h>


// http://graphics.stanford.edu/~seander/bithacks.html
static inline uint32
next_power_of_2(uint32 v)
{
	v--;
	v |= v >> 1;
	v |= v >> 2;
	v |= v >> 4;
	v |= v >> 8;
	v |= v >> 16;
	v++;

	return v;
}


// http://graphics.stanford.edu/~seander/bithacks.html
static inline uint32
count_set_bits(uint32 v)
{
	v = v - ((v >> 1) & 0x55555555);
	v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
	return (((v + (v >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24;
}


static inline uint32
log2(uint32 v)
{
	static const int MultiplyDeBruijnBitPosition[32] = {
		0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30,
		8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31
	};

	v |= v >> 1;
	v |= v >> 2;
	v |= v >> 4;
	v |= v >> 8;
	v |= v >> 16;

	return MultiplyDeBruijnBitPosition[(uint32)(v * 0x07C4ACDDU) >> 27];
}


#endif	// KERNEL_UTIL_BITUTIL_H