include/linux/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 <asm/byteorder.h>
  12
  13 /*
  14  * Bitfield access macros
  15  *
  16  * FIELD_{GET,PREP} macros take as first parameter shifted mask
  17  * from which they extract the base mask and shift amount.
  18  * Mask must be a compilation time constant.
  19  *
  20  * Example:
  21  *
  22  *  #include <linux/bitfield.h>
  23  *  #include <linux/bits.h>
  24  *
  25  *  #define REG_FIELD_A  GENMASK(6, 0)
  26  *  #define REG_FIELD_B  BIT(7)
  27  *  #define REG_FIELD_C  GENMASK(15, 8)
  28  *  #define REG_FIELD_D  GENMASK(31, 16)
  29  *
  30  * Get:
  31  *  a = FIELD_GET(REG_FIELD_A, reg);
  32  *  b = FIELD_GET(REG_FIELD_B, reg);
  33  *
  34  * Set:
  35  *  reg = FIELD_PREP(REG_FIELD_A, 1) |
  36  *        FIELD_PREP(REG_FIELD_B, 0) |
  37  *        FIELD_PREP(REG_FIELD_C, c) |
  38  *        FIELD_PREP(REG_FIELD_D, 0x40);
  39  *
  40  * Modify:
  41  *  reg &= ~REG_FIELD_C;
  42  *  reg |= FIELD_PREP(REG_FIELD_C, c);
  43  */
  44
  45 #define __bf_shf(x) (__builtin_ffsll(x) - 1)
  46
  47 #define __scalar_type_to_unsigned_cases(type)                           \
  48                 unsigned type:  (unsigned type)0,                       \
  49                 signed type:    (unsigned type)0
  50
  51 #define __unsigned_scalar_typeof(x) typeof(                             \
  52                 _Generic((x),                                           \
  53                         char:   (unsigned char)0,                       \
  54                         __scalar_type_to_unsigned_cases(char),          \
  55                         __scalar_type_to_unsigned_cases(short),         \
  56                         __scalar_type_to_unsigned_cases(int),           \
  57                         __scalar_type_to_unsigned_cases(long),          \
  58                         __scalar_type_to_unsigned_cases(long long),     \
  59                         default: (x)))
  60
  61 #define __bf_cast_unsigned(type, x)     ((__unsigned_scalar_typeof(type))(x))
  62
  63 #define __BF_FIELD_CHECK(_mask, _reg, _val, _pfx)                       \
  64         ({                                                              \
  65                 BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask),          \
  66                                  _pfx "mask is not constant");          \
  67                 BUILD_BUG_ON_MSG((_mask) == 0, _pfx "mask is zero");    \
  68                 BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ?           \
  69                                  ~((_mask) >> __bf_shf(_mask)) &        \
  70                                         (0 + (_val)) : 0,               \
  71                                  _pfx "value too large for the field"); \
  72                 BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask) >     \
  73                                  __bf_cast_unsigned(_reg, ~0ull),       \
  74                                  _pfx "type of reg too small for mask"); \
  75                 __BUILD_BUG_ON_NOT_POWER_OF_2((_mask) +                 \
  76                                               (1ULL << __bf_shf(_mask))); \
  77         })
  78
  79 /**
  80  * FIELD_MAX() - produce the maximum value representable by a field
  81  * @_mask: shifted mask defining the field's length and position
  82  *
  83  * FIELD_MAX() returns the maximum value that can be held in the field
  84  * specified by @_mask.
  85  */
  86 #define FIELD_MAX(_mask)                                                \
  87         ({                                                              \
  88                 __BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_MAX: ");     \
  89                 (typeof(_mask))((_mask) >> __bf_shf(_mask));            \
  90         })
  91
  92 /**
  93  * FIELD_FIT() - check if value fits in the field
  94  * @_mask: shifted mask defining the field's length and position
  95  * @_val:  value to test against the field
  96  *
  97  * Return: true if @_val can fit inside @_mask, false if @_val is too big.
  98  */
  99 #define FIELD_FIT(_mask, _val)                                          \
 100         ({                                                              \
 101                 __BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_FIT: ");     \
 102                 !((((typeof(_mask))_val) << __bf_shf(_mask)) & ~(_mask)); \
 103         })
 104
 105 /**
 106  * FIELD_PREP() - prepare a bitfield element
 107  * @_mask: shifted mask defining the field's length and position
 108  * @_val:  value to put in the field
 109  *
 110  * FIELD_PREP() masks and shifts up the value.  The result should
 111  * be combined with other fields of the bitfield using logical OR.
 112  */
 113 #define FIELD_PREP(_mask, _val)                                         \
 114         ({                                                              \
 115                 __BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: ");    \
 116                 ((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask);   \
 117         })
 118
 119 #define __BF_CHECK_POW2(n)      BUILD_BUG_ON_ZERO(((n) & ((n) - 1)) != 0)
 120
 121 /**
 122  * FIELD_PREP_CONST() - prepare a constant bitfield element
 123  * @_mask: shifted mask defining the field's length and position
 124  * @_val:  value to put in the field
 125  *
 126  * FIELD_PREP_CONST() masks and shifts up the value.  The result should
 127  * be combined with other fields of the bitfield using logical OR.
 128  *
 129  * Unlike FIELD_PREP() this is a constant expression and can therefore
 130  * be used in initializers. Error checking is less comfortable for this
 131  * version, and non-constant masks cannot be used.
 132  */
 133 #define FIELD_PREP_CONST(_mask, _val)                                   \
 134         (                                                               \
 135                 /* mask must be non-zero */                             \
 136                 BUILD_BUG_ON_ZERO((_mask) == 0) +                       \
 137                 /* check if value fits */                               \
 138                 BUILD_BUG_ON_ZERO(~((_mask) >> __bf_shf(_mask)) & (_val)) + \
 139                 /* check if mask is contiguous */                       \
 140                 __BF_CHECK_POW2((_mask) + (1ULL << __bf_shf(_mask))) +  \
 141                 /* and create the value */                              \
 142                 (((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask))  \
 143         )
 144
 145 /**
 146  * FIELD_GET() - extract a bitfield element
 147  * @_mask: shifted mask defining the field's length and position
 148  * @_reg:  value of entire bitfield
 149  *
 150  * FIELD_GET() extracts the field specified by @_mask from the
 151  * bitfield passed in as @_reg by masking and shifting it down.
 152  */
 153 #define FIELD_GET(_mask, _reg)                                          \
 154         ({                                                              \
 155                 __BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: ");       \
 156                 (typeof(_mask))(((_reg) & (_mask)) >> __bf_shf(_mask)); \
 157         })
 158
 159 extern void __compiletime_error("value doesn't fit into mask")
 160 __field_overflow(void);
 161 extern void __compiletime_error("bad bitfield mask")
 162 __bad_mask(void);
 163 static __always_inline u64 field_multiplier(u64 field)
 164 {
 165         if ((field | (field - 1)) & ((field | (field - 1)) + 1))
 166                 __bad_mask();
 167         return field & -field;
 168 }
 169 static __always_inline u64 field_mask(u64 field)
 170 {
 171         return field / field_multiplier(field);
 172 }
 173 #define field_max(field)        ((typeof(field))field_mask(field))
 174 #define ____MAKE_OP(type,base,to,from)                                  \
 175 static __always_inline __##type type##_encode_bits(base v, base field)  \
 176 {                                                                       \
 177         if (__builtin_constant_p(v) && (v & ~field_mask(field)))        \
 178                 __field_overflow();                                     \
 179         return to((v & field_mask(field)) * field_multiplier(field));   \
 180 }                                                                       \
 181 static __always_inline __##type type##_replace_bits(__##type old,       \
 182                                         base val, base field)           \
 183 {                                                                       \
 184         return (old & ~to(field)) | type##_encode_bits(val, field);     \
 185 }                                                                       \
 186 static __always_inline void type##p_replace_bits(__##type *p,           \
 187                                         base val, base field)           \
 188 {                                                                       \
 189         *p = (*p & ~to(field)) | type##_encode_bits(val, field);        \
 190 }                                                                       \
 191 static __always_inline base type##_get_bits(__##type v, base field)     \
 192 {                                                                       \
 193         return (from(v) & field)/field_multiplier(field);               \
 194 }
 195 #define __MAKE_OP(size)                                                 \
 196         ____MAKE_OP(le##size,u##size,cpu_to_le##size,le##size##_to_cpu) \
 197         ____MAKE_OP(be##size,u##size,cpu_to_be##size,be##size##_to_cpu) \
 198         ____MAKE_OP(u##size,u##size,,)
 199 ____MAKE_OP(u8,u8,,)
 200 __MAKE_OP(16)
 201 __MAKE_OP(32)
 202 __MAKE_OP(64)
 203 #undef __MAKE_OP
 204 #undef ____MAKE_OP
 205
 206 #endif