xref: /linux-6.15/include/linux/int_log.h (revision 9ab04d7e)

/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * Provides fixed-point logarithm operations.
 *
 * Copyright (C) 2006 Christoph Pfister ([email protected])
 */

#ifndef __LINUX_INT_LOG_H
#define __LINUX_INT_LOG_H

#include <linux/types.h>

/**
 * intlog2 - computes log2 of a value; the result is shifted left by 24 bits
 *
 * @value: The value (must be != 0)
 *
 * to use rational values you can use the following method:
 *
 *   intlog2(value) = intlog2(value * 2^x) - x * 2^24
 *
 * Some usecase examples:
 *
 *	intlog2(8) will give 3 << 24 = 3 * 2^24
 *
 *	intlog2(9) will give 3 << 24 + ... = 3.16... * 2^24
 *
 *	intlog2(1.5) = intlog2(3) - 2^24 = 0.584... * 2^24
 *
 *
 * return: log2(value) * 2^24
 */
extern unsigned int intlog2(u32 value);

/**
 * intlog10 - computes log10 of a value; the result is shifted left by 24 bits
 *
 * @value: The value (must be != 0)
 *
 * to use rational values you can use the following method:
 *
 *   intlog10(value) = intlog10(value * 10^x) - x * 2^24
 *
 * An usecase example:
 *
 *	intlog10(1000) will give 3 << 24 = 3 * 2^24
 *
 *   due to the implementation intlog10(1000) might be not exactly 3 * 2^24
 *
 * look at intlog2 for similar examples
 *
 * return: log10(value) * 2^24
 */
extern unsigned int intlog10(u32 value);

#endif