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/* SPDX-License-Identifier: GPL-2.0-only */
/*
* Copyright 2023 Red Hat
*/
#ifndef _LINUX_LOG2_H
#define _LINUX_LOG2_H
#include "permassert.h"
/* Compute the number of bits to represent n */
static inline unsigned int bits_per(unsigned int n)
{
unsigned int bits = 1;
while (n > 1) {
n >>= 1;
bits++;
}
return bits;
}
/**
* is_power_of_2() - Return true if and only if a number is a power of two.
*/
static inline bool is_power_of_2(uint64_t n)
{
return (n > 0) && ((n & (n - 1)) == 0);
}
/**
* ilog2() - Efficiently calculate the base-2 logarithm of a number truncated
* to an integer value.
* @n: The input value.
*
* This also happens to be the bit index of the highest-order non-zero bit in
* the binary representation of the number, which can easily be used to
* calculate the bit shift corresponding to a bit mask or an array capacity,
* or to calculate the binary floor or ceiling (next lowest or highest power
* of two).
*
* Return: The integer log2 of the value, or -1 if the value is zero.
*/
static inline int ilog2(uint64_t n)
{
VDO_ASSERT_LOG_ONLY(n != 0, "ilog2() may not be passed 0");
/*
* Many CPUs, including x86, directly support this calculation, so use
* the GCC function for counting the number of leading high-order zero
* bits.
*/
return 63 - __builtin_clzll(n);
}
#endif /* _LINUX_LOG2_H */
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