include/linux/bitfield.h

0001 /* SPDX-License-Identifier: GPL-2.0-only */
0002 /*
0003  * Copyright (C) 2014 Felix Fietkau <nbd@nbd.name>
0004  * Copyright (C) 2004 - 2009 Ivo van Doorn <IvDoorn@gmail.com>
0005  */
0006
0007 #ifndef _LINUX_BITFIELD_H
0008 #define _LINUX_BITFIELD_H
0009
0010 #include <linux/build_bug.h>
0011 #include <asm/byteorder.h>
0012
0013 /*
0014  * Bitfield access macros
0015  *
0016  * FIELD_{GET,PREP} macros take as first parameter shifted mask
0017  * from which they extract the base mask and shift amount.
0018  * Mask must be a compilation time constant.
0019  *
0020  * Example:
0021  *
0022  *  #include <linux/bitfield.h>
0023  *  #include <linux/bits.h>
0024  *
0025  *  #define REG_FIELD_A  GENMASK(6, 0)
0026  *  #define REG_FIELD_B  BIT(7)
0027  *  #define REG_FIELD_C  GENMASK(15, 8)
0028  *  #define REG_FIELD_D  GENMASK(31, 16)
0029  *
0030  * Get:
0031  *  a = FIELD_GET(REG_FIELD_A, reg);
0032  *  b = FIELD_GET(REG_FIELD_B, reg);
0033  *
0034  * Set:
0035  *  reg = FIELD_PREP(REG_FIELD_A, 1) |
0036  *    FIELD_PREP(REG_FIELD_B, 0) |
0037  *    FIELD_PREP(REG_FIELD_C, c) |
0038  *    FIELD_PREP(REG_FIELD_D, 0x40);
0039  *
0040  * Modify:
0041  *  reg &= ~REG_FIELD_C;
0042  *  reg |= FIELD_PREP(REG_FIELD_C, c);
0043  */
0044
0045 #define __bf_shf(x) (__builtin_ffsll(x) - 1)
0046
0047 #define __scalar_type_to_unsigned_cases(type)               \
0048         unsigned type:  (unsigned type)0,           \
0049         signed type:    (unsigned type)0
0050
0051 #define __unsigned_scalar_typeof(x) typeof(             \
0052         _Generic((x),                       \
0053             char:   (unsigned char)0,           \
0054             __scalar_type_to_unsigned_cases(char),      \
0055             __scalar_type_to_unsigned_cases(short),     \
0056             __scalar_type_to_unsigned_cases(int),       \
0057             __scalar_type_to_unsigned_cases(long),      \
0058             __scalar_type_to_unsigned_cases(long long), \
0059             default: (x)))
0060
0061 #define __bf_cast_unsigned(type, x) ((__unsigned_scalar_typeof(type))(x))
0062
0063 #define __BF_FIELD_CHECK(_mask, _reg, _val, _pfx)           \
0064     ({                              \
0065         BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask),      \
0066                  _pfx "mask is not constant");      \
0067         BUILD_BUG_ON_MSG((_mask) == 0, _pfx "mask is zero");    \
0068         BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ?       \
0069                  ~((_mask) >> __bf_shf(_mask)) & (_val) : 0, \
0070                  _pfx "value too large for the field"); \
0071         BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask) > \
0072                  __bf_cast_unsigned(_reg, ~0ull),   \
0073                  _pfx "type of reg too small for mask"); \
0074         __BUILD_BUG_ON_NOT_POWER_OF_2((_mask) +         \
0075                           (1ULL << __bf_shf(_mask))); \
0076     })
0077
0078 /**
0079  * FIELD_MAX() - produce the maximum value representable by a field
0080  * @_mask: shifted mask defining the field's length and position
0081  *
0082  * FIELD_MAX() returns the maximum value that can be held in the field
0083  * specified by @_mask.
0084  */
0085 #define FIELD_MAX(_mask)                        \
0086     ({                              \
0087         __BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_MAX: "); \
0088         (typeof(_mask))((_mask) >> __bf_shf(_mask));        \
0089     })
0090
0091 /**
0092  * FIELD_FIT() - check if value fits in the field
0093  * @_mask: shifted mask defining the field's length and position
0094  * @_val:  value to test against the field
0095  *
0096  * Return: true if @_val can fit inside @_mask, false if @_val is too big.
0097  */
0098 #define FIELD_FIT(_mask, _val)                      \
0099     ({                              \
0100         __BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_FIT: "); \
0101         !((((typeof(_mask))_val) << __bf_shf(_mask)) & ~(_mask)); \
0102     })
0103
0104 /**
0105  * FIELD_PREP() - prepare a bitfield element
0106  * @_mask: shifted mask defining the field's length and position
0107  * @_val:  value to put in the field
0108  *
0109  * FIELD_PREP() masks and shifts up the value.  The result should
0110  * be combined with other fields of the bitfield using logical OR.
0111  */
0112 #define FIELD_PREP(_mask, _val)                     \
0113     ({                              \
0114         __BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: ");    \
0115         ((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask);   \
0116     })
0117
0118 /**
0119  * FIELD_GET() - extract a bitfield element
0120  * @_mask: shifted mask defining the field's length and position
0121  * @_reg:  value of entire bitfield
0122  *
0123  * FIELD_GET() extracts the field specified by @_mask from the
0124  * bitfield passed in as @_reg by masking and shifting it down.
0125  */
0126 #define FIELD_GET(_mask, _reg)                      \
0127     ({                              \
0128         __BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: ");   \
0129         (typeof(_mask))(((_reg) & (_mask)) >> __bf_shf(_mask)); \
0130     })
0131
0132 extern void __compiletime_error("value doesn't fit into mask")
0133 __field_overflow(void);
0134 extern void __compiletime_error("bad bitfield mask")
0135 __bad_mask(void);
0136 static __always_inline u64 field_multiplier(u64 field)
0137 {
0138     if ((field | (field - 1)) & ((field | (field - 1)) + 1))
0139         __bad_mask();
0140     return field & -field;
0141 }
0142 static __always_inline u64 field_mask(u64 field)
0143 {
0144     return field / field_multiplier(field);
0145 }
0146 #define field_max(field)    ((typeof(field))field_mask(field))
0147 #define ____MAKE_OP(type,base,to,from)                  \
0148 static __always_inline __##type type##_encode_bits(base v, base field)  \
0149 {                                   \
0150     if (__builtin_constant_p(v) && (v & ~field_mask(field)))    \
0151         __field_overflow();                 \
0152     return to((v & field_mask(field)) * field_multiplier(field));   \
0153 }                                   \
0154 static __always_inline __##type type##_replace_bits(__##type old,   \
0155                     base val, base field)       \
0156 {                                   \
0157     return (old & ~to(field)) | type##_encode_bits(val, field); \
0158 }                                   \
0159 static __always_inline void type##p_replace_bits(__##type *p,       \
0160                     base val, base field)       \
0161 {                                   \
0162     *p = (*p & ~to(field)) | type##_encode_bits(val, field);    \
0163 }                                   \
0164 static __always_inline base type##_get_bits(__##type v, base field) \
0165 {                                   \
0166     return (from(v) & field)/field_multiplier(field);       \
0167 }
0168 #define __MAKE_OP(size)                         \
0169     ____MAKE_OP(le##size,u##size,cpu_to_le##size,le##size##_to_cpu) \
0170     ____MAKE_OP(be##size,u##size,cpu_to_be##size,be##size##_to_cpu) \
0171     ____MAKE_OP(u##size,u##size,,)
0172 ____MAKE_OP(u8,u8,,)
0173 __MAKE_OP(16)
0174 __MAKE_OP(32)
0175 __MAKE_OP(64)
0176 #undef __MAKE_OP
0177 #undef ____MAKE_OP
0178
0179 #endif