tools/include/linux/bitfield.h

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

File Facts

System
Linux kernel
Corpus path
tools/include/linux/bitfield.h
Extension
.h
Size
5486 bytes
Lines
178
Domain
Support Tooling And Documentation
Bucket
tools
Inferred role
Support Tooling And Documentation: implementation source
Status
source implementation candidate

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

#ifndef _LINUX_BITFIELD_H
#define _LINUX_BITFIELD_H

#include <linux/build_bug.h>
#include <linux/kernel.h>
#include <asm/byteorder.h>

/*
 * Bitfield access macros
 *
 * FIELD_{GET,PREP} macros take as first parameter shifted mask
 * from which they extract the base mask and shift amount.
 * Mask must be a compilation time constant.
 *
 * Example:
 *
 *  #define REG_FIELD_A  GENMASK(6, 0)
 *  #define REG_FIELD_B  BIT(7)
 *  #define REG_FIELD_C  GENMASK(15, 8)
 *  #define REG_FIELD_D  GENMASK(31, 16)
 *
 * Get:
 *  a = FIELD_GET(REG_FIELD_A, reg);
 *  b = FIELD_GET(REG_FIELD_B, reg);
 *
 * Set:
 *  reg = FIELD_PREP(REG_FIELD_A, 1) |
 *	  FIELD_PREP(REG_FIELD_B, 0) |
 *	  FIELD_PREP(REG_FIELD_C, c) |
 *	  FIELD_PREP(REG_FIELD_D, 0x40);
 *
 * Modify:
 *  reg &= ~REG_FIELD_C;
 *  reg |= FIELD_PREP(REG_FIELD_C, c);
 */

#define __bf_shf(x) (__builtin_ffsll(x) - 1)

#define __scalar_type_to_unsigned_cases(type)				\
		unsigned type:	(unsigned type)0,			\
		signed type:	(unsigned type)0

#define __unsigned_scalar_typeof(x) typeof(				\
		_Generic((x),						\
			char:	(unsigned char)0,			\
			__scalar_type_to_unsigned_cases(char),		\
			__scalar_type_to_unsigned_cases(short),		\
			__scalar_type_to_unsigned_cases(int),		\
			__scalar_type_to_unsigned_cases(long),		\
			__scalar_type_to_unsigned_cases(long long),	\
			default: (x)))

#define __bf_cast_unsigned(type, x)	((__unsigned_scalar_typeof(type))(x))

#define __BF_FIELD_CHECK(_mask, _reg, _val, _pfx)			\
	({								\
		BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask),		\
				 _pfx "mask is not constant");		\
		BUILD_BUG_ON_MSG((_mask) == 0, _pfx "mask is zero");	\
		BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ?		\
				 ~((_mask) >> __bf_shf(_mask)) & (_val) : 0, \
				 _pfx "value too large for the field"); \
		BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask) >	\
				 __bf_cast_unsigned(_reg, ~0ull),	\
				 _pfx "type of reg too small for mask"); \
		__BUILD_BUG_ON_NOT_POWER_OF_2((_mask) +			\
					      (1ULL << __bf_shf(_mask))); \
	})

/**
 * FIELD_MAX() - produce the maximum value representable by a field
 * @_mask: shifted mask defining the field's length and position
 *
 * FIELD_MAX() returns the maximum value that can be held in the field
 * specified by @_mask.
 */
#define FIELD_MAX(_mask)						\
	({								\
		__BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_MAX: ");	\
		(typeof(_mask))((_mask) >> __bf_shf(_mask));		\
	})

/**
 * FIELD_FIT() - check if value fits in the field
 * @_mask: shifted mask defining the field's length and position
 * @_val:  value to test against the field
 *
 * Return: true if @_val can fit inside @_mask, false if @_val is too big.
 */
#define FIELD_FIT(_mask, _val)						\

Annotation

Implementation Notes