include/linux/log2.h

Source file repositories/reference/linux-study-clean/include/linux/log2.h

File Facts

System
Linux kernel
Corpus path
include/linux/log2.h
Extension
.h
Size
6675 bytes
Lines
273
Domain
Core OS
Bucket
Core Kernel Interface
Inferred role
Core OS: implementation source
Status
source implementation candidate

Why This File Exists

Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.

Dependency Surface

Detected Declarations

Annotated Snippet

#ifndef _LINUX_LOG2_H
#define _LINUX_LOG2_H

#include <linux/types.h>
#include <linux/bitops.h>

/*
 * non-constant log of base 2 calculators
 * - the arch may override these in asm/bitops.h if they can be implemented
 *   more efficiently than using fls() and fls64()
 * - the arch is not required to handle n==0 if implementing the fallback
 */
#ifndef CONFIG_ARCH_HAS_ILOG2_U32
static __always_inline __attribute__((const))
int __ilog2_u32(u32 n)
{
	return fls(n) - 1;
}
#endif

#ifndef CONFIG_ARCH_HAS_ILOG2_U64
static __always_inline __attribute__((const))
int __ilog2_u64(u64 n)
{
	return fls64(n) - 1;
}
#endif

/**
 * is_power_of_2() - check if a value is a power of two
 * @n: the value to check
 *
 * Determine whether some value is a power of two, where zero is
 * *not* considered a power of two.
 * Return: true if @n is a power of 2, otherwise false.
 */
static __always_inline __attribute__((const))
bool is_power_of_2(unsigned long n)
{
	return n - 1 < (n ^ (n - 1));
}

/**
 * __roundup_pow_of_two() - round up to nearest power of two
 * @n: value to round up
 */
static inline __attribute__((const))
unsigned long __roundup_pow_of_two(unsigned long n)
{
	return 1UL << fls_long(n - 1);
}

/**
 * __rounddown_pow_of_two() - round down to nearest power of two
 * @n: value to round down
 */
static inline __attribute__((const))
unsigned long __rounddown_pow_of_two(unsigned long n)
{
	return 1UL << (fls_long(n) - 1);
}

/**
 * const_ilog2 - log base 2 of 32-bit or a 64-bit constant unsigned value
 * @n: parameter
 *
 * Use this where sparse expects a true constant expression, e.g. for array
 * indices.
 */
#define const_ilog2(n)				\
(						\
	__builtin_constant_p(n) ? (		\
		(n) < 2 ? 0 :			\
		(n) & (1ULL << 63) ? 63 :	\
		(n) & (1ULL << 62) ? 62 :	\
		(n) & (1ULL << 61) ? 61 :	\
		(n) & (1ULL << 60) ? 60 :	\
		(n) & (1ULL << 59) ? 59 :	\
		(n) & (1ULL << 58) ? 58 :	\
		(n) & (1ULL << 57) ? 57 :	\
		(n) & (1ULL << 56) ? 56 :	\
		(n) & (1ULL << 55) ? 55 :	\
		(n) & (1ULL << 54) ? 54 :	\
		(n) & (1ULL << 53) ? 53 :	\
		(n) & (1ULL << 52) ? 52 :	\
		(n) & (1ULL << 51) ? 51 :	\
		(n) & (1ULL << 50) ? 50 :	\
		(n) & (1ULL << 49) ? 49 :	\
		(n) & (1ULL << 48) ? 48 :	\
		(n) & (1ULL << 47) ? 47 :	\

Annotation

Implementation Notes