bitfield.h

  1/* SPDX-License-Identifier: GPL-2.0-only */
  2/*
  3 * Copyright (C) 2014 Felix Fietkau <nbd@nbd.name>
  4 * Copyright (C) 2004 - 2009 Ivo van Doorn <IvDoorn@gmail.com>
  5 */
  6
  7#ifndef _LINUX_BITFIELD_H
  8#define _LINUX_BITFIELD_H
  9
 10#include <linux/build_bug.h>
 11#include <linux/kernel.h>
 12#include <asm/byteorder.h>
 13
 14/*
 15 * Bitfield access macros
 16 *
 17 * FIELD_{GET,PREP} macros take as first parameter shifted mask
 18 * from which they extract the base mask and shift amount.
 19 * Mask must be a compilation time constant.
 20 *
 21 * Example:
 22 *
 23 *  #define REG_FIELD_A  GENMASK(6, 0)
 24 *  #define REG_FIELD_B  BIT(7)
 25 *  #define REG_FIELD_C  GENMASK(15, 8)
 26 *  #define REG_FIELD_D  GENMASK(31, 16)
 27 *
 28 * Get:
 29 *  a = FIELD_GET(REG_FIELD_A, reg);
 30 *  b = FIELD_GET(REG_FIELD_B, reg);
 31 *
 32 * Set:
 33 *  reg = FIELD_PREP(REG_FIELD_A, 1) |
 34 *	  FIELD_PREP(REG_FIELD_B, 0) |
 35 *	  FIELD_PREP(REG_FIELD_C, c) |
 36 *	  FIELD_PREP(REG_FIELD_D, 0x40);
 37 *
 38 * Modify:
 39 *  reg &= ~REG_FIELD_C;
 40 *  reg |= FIELD_PREP(REG_FIELD_C, c);
 41 */
 42
 43#define __bf_shf(x) (__builtin_ffsll(x) - 1)
 44
 45#define __scalar_type_to_unsigned_cases(type)				\
 46		unsigned type:	(unsigned type)0,			\
 47		signed type:	(unsigned type)0
 48
 49#define __unsigned_scalar_typeof(x) typeof(				\
 50		_Generic((x),						\
 51			char:	(unsigned char)0,			\
 52			__scalar_type_to_unsigned_cases(char),		\
 53			__scalar_type_to_unsigned_cases(short),		\
 54			__scalar_type_to_unsigned_cases(int),		\
 55			__scalar_type_to_unsigned_cases(long),		\
 56			__scalar_type_to_unsigned_cases(long long),	\
 57			default: (x)))
 58
 59#define __bf_cast_unsigned(type, x)	((__unsigned_scalar_typeof(type))(x))
 60
 61#define __BF_FIELD_CHECK(_mask, _reg, _val, _pfx)			\
 62	({								\
 63		BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask),		\
 64				 _pfx "mask is not constant");		\
 65		BUILD_BUG_ON_MSG((_mask) == 0, _pfx "mask is zero");	\
 66		BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ?		\
 67				 ~((_mask) >> __bf_shf(_mask)) & (_val) : 0, \
 68				 _pfx "value too large for the field"); \
 69		BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask) >	\
 70				 __bf_cast_unsigned(_reg, ~0ull),	\
 71				 _pfx "type of reg too small for mask"); \
 72		__BUILD_BUG_ON_NOT_POWER_OF_2((_mask) +			\
 73					      (1ULL << __bf_shf(_mask))); \
 74	})
 75
 76/**
 77 * FIELD_MAX() - produce the maximum value representable by a field
 78 * @_mask: shifted mask defining the field's length and position
 79 *
 80 * FIELD_MAX() returns the maximum value that can be held in the field
 81 * specified by @_mask.
 82 */
 83#define FIELD_MAX(_mask)						\
 84	({								\
 85		__BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_MAX: ");	\
 86		(typeof(_mask))((_mask) >> __bf_shf(_mask));		\
 87	})
 88
 89/**
 90 * FIELD_FIT() - check if value fits in the field
 91 * @_mask: shifted mask defining the field's length and position
 92 * @_val:  value to test against the field
 93 *
 94 * Return: true if @_val can fit inside @_mask, false if @_val is too big.
 95 */
 96#define FIELD_FIT(_mask, _val)						\
 97	({								\
 98		__BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_FIT: ");	\
 99		!((((typeof(_mask))_val) << __bf_shf(_mask)) & ~(_mask)); \
100	})
101
102/**
103 * FIELD_PREP() - prepare a bitfield element
104 * @_mask: shifted mask defining the field's length and position
105 * @_val:  value to put in the field
106 *
107 * FIELD_PREP() masks and shifts up the value.  The result should
108 * be combined with other fields of the bitfield using logical OR.
109 */
110#define FIELD_PREP(_mask, _val)						\
111	({								\
112		__BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: ");	\
113		((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask);	\
114	})
115
116/**
117 * FIELD_GET() - extract a bitfield element
118 * @_mask: shifted mask defining the field's length and position
119 * @_reg:  value of entire bitfield
120 *
121 * FIELD_GET() extracts the field specified by @_mask from the
122 * bitfield passed in as @_reg by masking and shifting it down.
123 */
124#define FIELD_GET(_mask, _reg)						\
125	({								\
126		__BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: ");	\
127		(typeof(_mask))(((_reg) & (_mask)) >> __bf_shf(_mask));	\
128	})
129
130extern void __compiletime_error("value doesn't fit into mask")
131__field_overflow(void);
132extern void __compiletime_error("bad bitfield mask")
133__bad_mask(void);
134static __always_inline u64 field_multiplier(u64 field)
135{
136	if ((field | (field - 1)) & ((field | (field - 1)) + 1))
137		__bad_mask();
138	return field & -field;
139}
140static __always_inline u64 field_mask(u64 field)
141{
142	return field / field_multiplier(field);
143}
144#define field_max(field)	((typeof(field))field_mask(field))
145#define ____MAKE_OP(type,base,to,from)					\
146static __always_inline __##type type##_encode_bits(base v, base field)	\
147{									\
148	if (__builtin_constant_p(v) && (v & ~field_mask(field)))	\
149		__field_overflow();					\
150	return to((v & field_mask(field)) * field_multiplier(field));	\
151}									\
152static __always_inline __##type type##_replace_bits(__##type old,	\
153					base val, base field)		\
154{									\
155	return (old & ~to(field)) | type##_encode_bits(val, field);	\
156}									\
157static __always_inline void type##p_replace_bits(__##type *p,		\
158					base val, base field)		\
159{									\
160	*p = (*p & ~to(field)) | type##_encode_bits(val, field);	\
161}									\
162static __always_inline base type##_get_bits(__##type v, base field)	\
163{									\
164	return (from(v) & field)/field_multiplier(field);		\
165}
166#define __MAKE_OP(size)							\
167	____MAKE_OP(le##size,u##size,cpu_to_le##size,le##size##_to_cpu)	\
168	____MAKE_OP(be##size,u##size,cpu_to_be##size,be##size##_to_cpu)	\
169	____MAKE_OP(u##size,u##size,,)
170____MAKE_OP(u8,u8,,)
171__MAKE_OP(16)
172__MAKE_OP(32)
173__MAKE_OP(64)
174#undef __MAKE_OP
175#undef ____MAKE_OP
176
177#endif