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/typecheck.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 * field_{get,prep} are variants that take a non-const mask.
 21 *
 22 * Example:
 23 *
 24 *  #include <linux/bitfield.h>
 25 *  #include <linux/bits.h>
 26 *
 27 *  #define REG_FIELD_A  GENMASK(6, 0)
 28 *  #define REG_FIELD_B  BIT(7)
 29 *  #define REG_FIELD_C  GENMASK(15, 8)
 30 *  #define REG_FIELD_D  GENMASK(31, 16)
 31 *
 32 * Get:
 33 *  a = FIELD_GET(REG_FIELD_A, reg);
 34 *  b = FIELD_GET(REG_FIELD_B, reg);
 35 *
 36 * Set:
 37 *  reg = FIELD_PREP(REG_FIELD_A, 1) |
 38 *	  FIELD_PREP(REG_FIELD_B, 0) |
 39 *	  FIELD_PREP(REG_FIELD_C, c) |
 40 *	  FIELD_PREP(REG_FIELD_D, 0x40);
 41 *
 42 * Modify:
 43 *  FIELD_MODIFY(REG_FIELD_C, &reg, c);
 44 */
 45
 46#define __bf_shf(x) (__builtin_ffsll(x) - 1)
 47
 48#define __scalar_type_to_unsigned_cases(type)				\
 49		unsigned type:	(unsigned type)0,			\
 50		signed type:	(unsigned type)0
 51
 52#define __unsigned_scalar_typeof(x) typeof(				\
 53		_Generic((x),						\
 54			char:	(unsigned char)0,			\
 55			__scalar_type_to_unsigned_cases(char),		\
 56			__scalar_type_to_unsigned_cases(short),		\
 57			__scalar_type_to_unsigned_cases(int),		\
 58			__scalar_type_to_unsigned_cases(long),		\
 59			__scalar_type_to_unsigned_cases(long long),	\
 60			default: (x)))
 61
 62#define __bf_cast_unsigned(type, x)	((__unsigned_scalar_typeof(type))(x))
 63
 64#define __BF_FIELD_CHECK_MASK(_mask, _val, _pfx)			\
 65	({								\
 66		BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask),		\
 67				 _pfx "mask is not constant");		\
 68		BUILD_BUG_ON_MSG((_mask) == 0, _pfx "mask is zero");	\
 69		BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ?		\
 70				 ~((_mask) >> __bf_shf(_mask)) &	\
 71					(0 + (_val)) : 0,		\
 72				 _pfx "value too large for the field"); \
 73		__BUILD_BUG_ON_NOT_POWER_OF_2((_mask) +			\
 74					      (1ULL << __bf_shf(_mask))); \
 75	})
 76
 77#define __BF_FIELD_CHECK_REG(mask, reg, pfx)				\
 78	BUILD_BUG_ON_MSG(__bf_cast_unsigned(mask, mask) >		\
 79			 __bf_cast_unsigned(reg, ~0ull),		\
 80			 pfx "type of reg too small for mask")
 81
 82#define __BF_FIELD_CHECK(mask, reg, val, pfx)				\
 83	({								\
 84		__BF_FIELD_CHECK_MASK(mask, val, pfx);			\
 85		__BF_FIELD_CHECK_REG(mask, reg, pfx);			\
 86	})
 87
 88#define __FIELD_PREP(mask, val, pfx)					\
 89	({								\
 90		__BF_FIELD_CHECK_MASK(mask, val, pfx);			\
 91		((typeof(mask))(val) << __bf_shf(mask)) & (mask);	\
 92	})
 93
 94#define __FIELD_GET(mask, reg, pfx)					\
 95	({								\
 96		__BF_FIELD_CHECK_MASK(mask, 0U, pfx);			\
 97		(typeof(mask))(((reg) & (mask)) >> __bf_shf(mask));	\
 98	})
 99
100/**
101 * FIELD_MAX() - produce the maximum value representable by a field
102 * @_mask: shifted mask defining the field's length and position
103 *
104 * FIELD_MAX() returns the maximum value that can be held in the field
105 * specified by @_mask.
106 */
107#define FIELD_MAX(_mask)						\
108	({								\
109		__BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_MAX: ");	\
110		(typeof(_mask))((_mask) >> __bf_shf(_mask));		\
111	})
112
113/**
114 * FIELD_FIT() - check if value fits in the field
115 * @_mask: shifted mask defining the field's length and position
116 * @_val:  value to test against the field
117 *
118 * Return: true if @_val can fit inside @_mask, false if @_val is too big.
119 */
120#define FIELD_FIT(_mask, _val)						\
121	({								\
122		__BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_FIT: ");	\
123		!((((typeof(_mask))_val) << __bf_shf(_mask)) & ~(_mask)); \
124	})
125
126/**
127 * FIELD_PREP() - prepare a bitfield element
128 * @_mask: shifted mask defining the field's length and position
129 * @_val:  value to put in the field
130 *
131 * FIELD_PREP() masks and shifts up the value.  The result should
132 * be combined with other fields of the bitfield using logical OR.
133 */
134#define FIELD_PREP(_mask, _val)						\
135	({								\
136		__BF_FIELD_CHECK_REG(_mask, 0ULL, "FIELD_PREP: ");	\
137		__FIELD_PREP(_mask, _val, "FIELD_PREP: ");		\
138	})
139
140#define __BF_CHECK_POW2(n)	BUILD_BUG_ON_ZERO(((n) & ((n) - 1)) != 0)
141
142/**
143 * FIELD_PREP_CONST() - prepare a constant bitfield element
144 * @_mask: shifted mask defining the field's length and position
145 * @_val:  value to put in the field
146 *
147 * FIELD_PREP_CONST() masks and shifts up the value.  The result should
148 * be combined with other fields of the bitfield using logical OR.
149 *
150 * Unlike FIELD_PREP() this is a constant expression and can therefore
151 * be used in initializers. Error checking is less comfortable for this
152 * version, and non-constant masks cannot be used.
153 */
154#define FIELD_PREP_CONST(_mask, _val)					\
155	(								\
156		/* mask must be non-zero */				\
157		BUILD_BUG_ON_ZERO((_mask) == 0) +			\
158		/* check if value fits */				\
159		BUILD_BUG_ON_ZERO(~((_mask) >> __bf_shf(_mask)) & (_val)) + \
160		/* check if mask is contiguous */			\
161		__BF_CHECK_POW2((_mask) + (1ULL << __bf_shf(_mask))) +	\
162		/* and create the value */				\
163		(((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask))	\
164	)
165
166/**
167 * FIELD_GET() - extract a bitfield element
168 * @_mask: shifted mask defining the field's length and position
169 * @_reg:  value of entire bitfield
170 *
171 * FIELD_GET() extracts the field specified by @_mask from the
172 * bitfield passed in as @_reg by masking and shifting it down.
173 */
174#define FIELD_GET(_mask, _reg)						\
175	({								\
176		__BF_FIELD_CHECK_REG(_mask, _reg, "FIELD_GET: ");	\
177		__FIELD_GET(_mask, _reg, "FIELD_GET: ");		\
178	})
179
180/**
181 * FIELD_MODIFY() - modify a bitfield element
182 * @_mask: shifted mask defining the field's length and position
183 * @_reg_p: pointer to the memory that should be updated
184 * @_val: value to store in the bitfield
185 *
186 * FIELD_MODIFY() modifies the set of bits in @_reg_p specified by @_mask,
187 * by replacing them with the bitfield value passed in as @_val.
188 */
189#define FIELD_MODIFY(_mask, _reg_p, _val)						\
190	({										\
191		typecheck_pointer(_reg_p);						\
192		__BF_FIELD_CHECK(_mask, *(_reg_p), _val, "FIELD_MODIFY: ");		\
193		*(_reg_p) &= ~(_mask);							\
194		*(_reg_p) |= (((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask));	\
195	})
196
197extern void __compiletime_error("value doesn't fit into mask")
198__field_overflow(void);
199extern void __compiletime_error("bad bitfield mask")
200__bad_mask(void);
201static __always_inline u64 field_multiplier(u64 field)
202{
203	if ((field | (field - 1)) & ((field | (field - 1)) + 1))
204		__bad_mask();
205	return field & -field;
206}
207static __always_inline u64 field_mask(u64 field)
208{
209	return field / field_multiplier(field);
210}
211#define field_max(field)	((typeof(field))field_mask(field))
212#define ____MAKE_OP(type,base,to,from)					\
213static __always_inline __##type __must_check type##_encode_bits(base v, base field)	\
214{									\
215	if (__builtin_constant_p(v) && (v & ~field_mask(field)))	\
216		__field_overflow();					\
217	return to((v & field_mask(field)) * field_multiplier(field));	\
218}									\
219static __always_inline __##type __must_check type##_replace_bits(__##type old,	\
220							base val, base field)	\
221{									\
222	return (old & ~to(field)) | type##_encode_bits(val, field);	\
223}									\
224static __always_inline void type##p_replace_bits(__##type *p,		\
225					base val, base field)		\
226{									\
227	*p = (*p & ~to(field)) | type##_encode_bits(val, field);	\
228}									\
229static __always_inline base __must_check type##_get_bits(__##type v, base field)	\
230{									\
231	return (from(v) & field)/field_multiplier(field);		\
232}
233#define __MAKE_OP(size)							\
234	____MAKE_OP(le##size,u##size,cpu_to_le##size,le##size##_to_cpu)	\
235	____MAKE_OP(be##size,u##size,cpu_to_be##size,be##size##_to_cpu)	\
236	____MAKE_OP(u##size,u##size,,)
237____MAKE_OP(u8,u8,,)
238__MAKE_OP(16)
239__MAKE_OP(32)
240__MAKE_OP(64)
241#undef __MAKE_OP
242#undef ____MAKE_OP
243
244#define __field_prep(mask, val)						\
245	({								\
246		__auto_type __mask = (mask);				\
247		typeof(__mask) __val = (val);				\
248		unsigned int __shift = BITS_PER_TYPE(__mask) <= 32 ?	\
249				       __ffs(__mask) : __ffs64(__mask);	\
250		(__val << __shift) & __mask;				\
251	})
252
253#define __field_get(mask, reg)						\
254	({								\
255		__auto_type __mask = (mask);				\
256		typeof(__mask) __reg =  (reg);				\
257		unsigned int __shift = BITS_PER_TYPE(__mask) <= 32 ?	\
258				       __ffs(__mask) : __ffs64(__mask);	\
259		(__reg & __mask) >> __shift;				\
260	})
261
262/**
263 * field_prep() - prepare a bitfield element
264 * @mask: shifted mask defining the field's length and position, must be
265 *        non-zero
266 * @val:  value to put in the field
267 *
268 * Return: field value masked and shifted to its final destination
269 *
270 * field_prep() masks and shifts up the value.  The result should be
271 * combined with other fields of the bitfield using logical OR.
272 * Unlike FIELD_PREP(), @mask is not limited to a compile-time constant.
273 * Typical usage patterns are a value stored in a table, or calculated by
274 * shifting a constant by a variable number of bits.
275 * If you want to ensure that @mask is a compile-time constant, please use
276 * FIELD_PREP() directly instead.
277 */
278#define field_prep(mask, val)						\
279	(__builtin_constant_p(mask) ? __FIELD_PREP(mask, val, "field_prep: ") \
280				    : __field_prep(mask, val))
281
282/**
283 * field_get() - extract a bitfield element
284 * @mask: shifted mask defining the field's length and position, must be
285 *        non-zero
286 * @reg:  value of entire bitfield
287 *
288 * Return: extracted field value
289 *
290 * field_get() extracts the field specified by @mask from the
291 * bitfield passed in as @reg by masking and shifting it down.
292 * Unlike FIELD_GET(), @mask is not limited to a compile-time constant.
293 * Typical usage patterns are a value stored in a table, or calculated by
294 * shifting a constant by a variable number of bits.
295 * If you want to ensure that @mask is a compile-time constant, please use
296 * FIELD_GET() directly instead.
297 */
298#define field_get(mask, reg)						\
299	(__builtin_constant_p(mask) ? __FIELD_GET(mask, reg, "field_get: ") \
300				    : __field_get(mask, reg))
301
302#endif