lib/bitfield.h

   1 /* SPDX-License-Identifier: MIT
   2  *
   3  * Copyright 2010-2019 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   4  */
   5
   6 #ifndef _BABELTRACE_BITFIELD_H
   7 #define _BABELTRACE_BITFIELD_H
   8
   9 #include <linux/types.h>
  10 #include <lttng-endian.h>
  11
  12 #ifndef CHAR_BIT
  13 #define CHAR_BIT 8
  14 #endif
  15
  16 /*
  17  * This header strictly follows the C99 standard, except for use of the
  18  * compiler-specific __typeof__.
  19  */
  20
  21 /*
  22  * This bitfield header requires the compiler representation of signed
  23  * integers to be two's complement.
  24  */
  25 #if (-1 != ~0)
  26 #error "bitfield.h requires the compiler representation of signed integers to be two's complement."
  27 #endif
  28
  29 /*
  30  * _bt_is_signed_type() willingly generates comparison of unsigned
  31  * expression < 0, which is always false. Silence compiler warnings.
  32  */
  33 #ifdef __GNUC__
  34 # define _BT_DIAG_PUSH                  _Pragma("GCC diagnostic push")
  35 # define _BT_DIAG_POP                   _Pragma("GCC diagnostic pop")
  36
  37 # define _BT_DIAG_STRINGIFY_1(x)        #x
  38 # define _BT_DIAG_STRINGIFY(x)          _BT_DIAG_STRINGIFY_1(x)
  39
  40 # define _BT_DIAG_IGNORE(option)        \
  41         _Pragma(_BT_DIAG_STRINGIFY(GCC diagnostic ignored option))
  42 # define _BT_DIAG_IGNORE_TYPE_LIMITS    _BT_DIAG_IGNORE("-Wtype-limits")
  43 #else
  44 # define _BT_DIAG_PUSH
  45 # define _BT_DIAG_POP
  46 # define _BT_DIAG_IGNORE
  47 # define _BT_DIAG_IGNORE_TYPE_LIMITS
  48 #endif
  49
  50 #define _bt_is_signed_type(type)        ((type) -1 < (type) 0)
  51
  52 /*
  53  * Produce a build-time error if the condition `cond` is non-zero.
  54  * Evaluates as a size_t expression.
  55  */
  56 #define _BT_BUILD_ASSERT(cond)                                  \
  57         sizeof(struct { int f:(2 * !!(cond) - 1); })
  58
  59 /*
  60  * Cast value `v` to an unsigned integer of the same size as `v`.
  61  */
  62 #define _bt_cast_value_to_unsigned(v)                                   \
  63         (sizeof(v) == sizeof(uint8_t) ? (uint8_t) (v) :                 \
  64         sizeof(v) == sizeof(uint16_t) ? (uint16_t) (v) :                \
  65         sizeof(v) == sizeof(uint32_t) ? (uint32_t) (v) :                \
  66         sizeof(v) == sizeof(uint64_t) ? (uint64_t) (v) :                \
  67         _BT_BUILD_ASSERT(sizeof(v) <= sizeof(uint64_t)))
  68
  69 /*
  70  * Cast value `v` to an unsigned integer type of the size of type `type`
  71  * *without* sign-extension.
  72  *
  73  * The unsigned cast ensures that we're not shifting a negative value,
  74  * which is undefined in C. However, this limits the maximum type size
  75  * of `type` to 64-bit. Generate a compile-time error if the size of
  76  * `type` is larger than 64-bit.
  77  */
  78 #define _bt_cast_value_to_unsigned_type(type, v)                        \
  79         (sizeof(type) == sizeof(uint8_t) ?                              \
  80                 (uint8_t) _bt_cast_value_to_unsigned(v) :               \
  81         sizeof(type) == sizeof(uint16_t) ?                              \
  82                 (uint16_t) _bt_cast_value_to_unsigned(v) :              \
  83         sizeof(type) == sizeof(uint32_t) ?                              \
  84                 (uint32_t) _bt_cast_value_to_unsigned(v) :              \
  85         sizeof(type) == sizeof(uint64_t) ?                              \
  86                 (uint64_t) _bt_cast_value_to_unsigned(v) :              \
  87         _BT_BUILD_ASSERT(sizeof(v) <= sizeof(uint64_t)))
  88
  89 /*
  90  * _bt_fill_mask evaluates to a "type" integer with all bits set.
  91  */
  92 #define _bt_fill_mask(type)     ((type) ~(type) 0)
  93
  94 /*
  95  * Left shift a value `v` of `shift` bits.
  96  *
  97  * The type of `v` can be signed or unsigned integer.
  98  * The value of `shift` must be less than the size of `v` (in bits),
  99  * otherwise the behavior is undefined.
 100  * Evaluates to the result of the shift operation.
 101  *
 102  * According to the C99 standard, left shift of a left hand-side signed
 103  * type is undefined if it has a negative value or if the result cannot
 104  * be represented in the result type. This bitfield header discards the
 105  * bits that are left-shifted beyond the result type representation,
 106  * which is the behavior of an unsigned type left shift operation.
 107  * Therefore, always perform left shift on an unsigned type.
 108  *
 109  * This macro should not be used if `shift` can be greater or equal than
 110  * the bitwidth of `v`. See `_bt_safe_lshift`.
 111  */
 112 #define _bt_lshift(v, shift)                                            \
 113         ((__typeof__(v)) (_bt_cast_value_to_unsigned(v) << (shift)))
 114
 115 /*
 116  * Generate a mask of type `type` with the `length` least significant bits
 117  * cleared, and the most significant bits set.
 118  */
 119 #define _bt_make_mask_complement(type, length)                          \
 120         _bt_lshift(_bt_fill_mask(type), length)
 121
 122 /*
 123  * Generate a mask of type `type` with the `length` least significant bits
 124  * set, and the most significant bits cleared.
 125  */
 126 #define _bt_make_mask(type, length)                                     \
 127         ((type) ~_bt_make_mask_complement(type, length))
 128
 129 /*
 130  * Right shift a value `v` of `shift` bits.
 131  *
 132  * The type of `v` can be signed or unsigned integer.
 133  * The value of `shift` must be less than the size of `v` (in bits),
 134  * otherwise the behavior is undefined.
 135  * Evaluates to the result of the shift operation.
 136  *
 137  * According to the C99 standard, right shift of a left hand-side signed
 138  * type which has a negative value is implementation defined. This
 139  * bitfield header relies on the right shift implementation carrying the
 140  * sign bit. If the compiler implementation has a different behavior,
 141  * emulate carrying the sign bit.
 142  *
 143  * This macro should not be used if `shift` can be greater or equal than
 144  * the bitwidth of `v`. See `_bt_safe_rshift`.
 145  */
 146 #if ((-1 >> 1) == -1)
 147 #define _bt_rshift(v, shift)    ((v) >> (shift))
 148 #else
 149 #define _bt_rshift(v, shift)                                            \
 150         ((__typeof__(v)) ((_bt_cast_value_to_unsigned(v) >> (shift)) |  \
 151                 ((v) < 0 ? _bt_make_mask_complement(__typeof__(v),      \
 152                         sizeof(v) * CHAR_BIT - (shift)) : 0)))
 153 #endif
 154
 155 /*
 156  * Right shift a signed or unsigned integer with `shift` value being an
 157  * arbitrary number of bits. `v` is modified by this macro. The shift
 158  * is transformed into a sequence of `_nr_partial_shifts` consecutive
 159  * shift operations, each of a number of bits smaller than the bitwidth
 160  * of `v`, ending with a shift of the number of left over bits.
 161  */
 162 #define _bt_safe_rshift(v, shift)                                       \
 163 do {                                                                    \
 164         unsigned long _nr_partial_shifts = (shift) / (sizeof(v) * CHAR_BIT - 1); \
 165         unsigned long _leftover_bits = (shift) % (sizeof(v) * CHAR_BIT - 1); \
 166                                                                         \
 167         for (; _nr_partial_shifts; _nr_partial_shifts--)                \
 168                 (v) = _bt_rshift(v, sizeof(v) * CHAR_BIT - 1);          \
 169         (v) = _bt_rshift(v, _leftover_bits);                            \
 170 } while (0)
 171
 172 /*
 173  * Left shift a signed or unsigned integer with `shift` value being an
 174  * arbitrary number of bits. `v` is modified by this macro. The shift
 175  * is transformed into a sequence of `_nr_partial_shifts` consecutive
 176  * shift operations, each of a number of bits smaller than the bitwidth
 177  * of `v`, ending with a shift of the number of left over bits.
 178  */
 179 #define _bt_safe_lshift(v, shift)                                       \
 180 do {                                                                    \
 181         unsigned long _nr_partial_shifts = (shift) / (sizeof(v) * CHAR_BIT - 1); \
 182         unsigned long _leftover_bits = (shift) % (sizeof(v) * CHAR_BIT - 1); \
 183                                                                         \
 184         for (; _nr_partial_shifts; _nr_partial_shifts--)                \
 185                 (v) = _bt_lshift(v, sizeof(v) * CHAR_BIT - 1);          \
 186         (v) = _bt_lshift(v, _leftover_bits);                            \
 187 } while (0)
 188
 189 /*
 190  * bt_bitfield_write - write integer to a bitfield in native endianness
 191  *
 192  * Save integer to the bitfield, which starts at the "start" bit, has "len"
 193  * bits.
 194  * The inside of a bitfield is from high bits to low bits.
 195  * Uses native endianness.
 196  * For unsigned "v", pad MSB with 0 if bitfield is larger than v.
 197  * For signed "v", sign-extend v if bitfield is larger than v.
 198  *
 199  * On little endian, bytes are placed from the less significant to the most
 200  * significant. Also, consecutive bitfields are placed from lower bits to higher
 201  * bits.
 202  *
 203  * On big endian, bytes are places from most significant to less significant.
 204  * Also, consecutive bitfields are placed from higher to lower bits.
 205  */
 206
 207 #define _bt_bitfield_write_le(ptr, type, start, length, v)              \
 208 do {                                                                    \
 209         __typeof__(v) _v = (v);                                 \
 210         type *_ptr = (void *) (ptr);                                    \
 211         unsigned long _start = (start), _length = (length);             \
 212         type _mask, _cmask;                                             \
 213         unsigned long _ts = sizeof(type) * CHAR_BIT; /* type size */    \
 214         unsigned long _start_unit, _end_unit, _this_unit;               \
 215         unsigned long _end, _cshift; /* _cshift is "complement shift" */ \
 216                                                                         \
 217         if (!_length)                                                   \
 218                 break;                                                  \
 219                                                                         \
 220         _end = _start + _length;                                        \
 221         _start_unit = _start / _ts;                                     \
 222         _end_unit = (_end + (_ts - 1)) / _ts;                           \
 223                                                                         \
 224         /* Trim v high bits */                                          \
 225         if (_length < sizeof(_v) * CHAR_BIT)                            \
 226                 _v &= _bt_make_mask(__typeof__(_v), _length);           \
 227                                                                         \
 228         /* We can now append v with a simple "or", shift it piece-wise */ \
 229         _this_unit = _start_unit;                                       \
 230         if (_start_unit == _end_unit - 1) {                             \
 231                 _mask = _bt_make_mask(type, _start % _ts);              \
 232                 if (_end % _ts)                                         \
 233                         _mask |= _bt_make_mask_complement(type, _end % _ts); \
 234                 _cmask = _bt_lshift((type) (_v), _start % _ts);         \
 235                 _cmask &= ~_mask;                                       \
 236                 _ptr[_this_unit] &= _mask;                              \
 237                 _ptr[_this_unit] |= _cmask;                             \
 238                 break;                                                  \
 239         }                                                               \
 240         if (_start % _ts) {                                             \
 241                 _cshift = _start % _ts;                                 \
 242                 _mask = _bt_make_mask(type, _cshift);                   \
 243                 _cmask = _bt_lshift((type) (_v), _cshift);              \
 244                 _cmask &= ~_mask;                                       \
 245                 _ptr[_this_unit] &= _mask;                              \
 246                 _ptr[_this_unit] |= _cmask;                             \
 247                 _bt_safe_rshift(_v, _ts - _cshift);                     \
 248                 _start += _ts - _cshift;                                \
 249                 _this_unit++;                                           \
 250         }                                                               \
 251         for (; _this_unit < _end_unit - 1; _this_unit++) {              \
 252                 _ptr[_this_unit] = (type) _v;                           \
 253                 _bt_safe_rshift(_v, _ts);                               \
 254                 _start += _ts;                                          \
 255         }                                                               \
 256         if (_end % _ts) {                                               \
 257                 _mask = _bt_make_mask_complement(type, _end % _ts);     \
 258                 _cmask = (type) _v;                                     \
 259                 _cmask &= ~_mask;                                       \
 260                 _ptr[_this_unit] &= _mask;                              \
 261                 _ptr[_this_unit] |= _cmask;                             \
 262         } else                                                          \
 263                 _ptr[_this_unit] = (type) _v;                           \
 264 } while (0)
 265
 266 #define _bt_bitfield_write_be(ptr, type, start, length, v)              \
 267 do {                                                                    \
 268         __typeof__(v) _v = (v);                                         \
 269         type *_ptr = (void *) (ptr);                                    \
 270         unsigned long _start = (start), _length = (length);             \
 271         type _mask, _cmask;                                             \
 272         unsigned long _ts = sizeof(type) * CHAR_BIT; /* type size */    \
 273         unsigned long _start_unit, _end_unit, _this_unit;               \
 274         unsigned long _end, _cshift; /* _cshift is "complement shift" */ \
 275                                                                         \
 276         if (!_length)                                                   \
 277                 break;                                                  \
 278                                                                         \
 279         _end = _start + _length;                                        \
 280         _start_unit = _start / _ts;                                     \
 281         _end_unit = (_end + (_ts - 1)) / _ts;                           \
 282                                                                         \
 283         /* Trim v high bits */                                          \
 284         if (_length < sizeof(_v) * CHAR_BIT)                            \
 285                 _v &= _bt_make_mask(__typeof__(_v), _length);           \
 286                                                                         \
 287         /* We can now append v with a simple "or", shift it piece-wise */ \
 288         _this_unit = _end_unit - 1;                                     \
 289         if (_start_unit == _end_unit - 1) {                             \
 290                 _mask = _bt_make_mask(type, (_ts - (_end % _ts)) % _ts); \
 291                 if (_start % _ts)                                       \
 292                         _mask |= _bt_make_mask_complement(type, _ts - (_start % _ts)); \
 293                 _cmask = _bt_lshift((type) (_v), (_ts - (_end % _ts)) % _ts); \
 294                 _cmask &= ~_mask;                                       \
 295                 _ptr[_this_unit] &= _mask;                              \
 296                 _ptr[_this_unit] |= _cmask;                             \
 297                 break;                                                  \
 298         }                                                               \
 299         if (_end % _ts) {                                               \
 300                 _cshift = _end % _ts;                                   \
 301                 _mask = _bt_make_mask(type, _ts - _cshift);             \
 302                 _cmask = _bt_lshift((type) (_v), _ts - _cshift);        \
 303                 _cmask &= ~_mask;                                       \
 304                 _ptr[_this_unit] &= _mask;                              \
 305                 _ptr[_this_unit] |= _cmask;                             \
 306                 _bt_safe_rshift(_v, _cshift);                           \
 307                 _end -= _cshift;                                        \
 308                 _this_unit--;                                           \
 309         }                                                               \
 310         for (; (long) _this_unit >= (long) _start_unit + 1; _this_unit--) { \
 311                 _ptr[_this_unit] = (type) _v;                           \
 312                 _bt_safe_rshift(_v, _ts);                               \
 313                 _end -= _ts;                                            \
 314         }                                                               \
 315         if (_start % _ts) {                                             \
 316                 _mask = _bt_make_mask_complement(type, _ts - (_start % _ts)); \
 317                 _cmask = (type) _v;                                     \
 318                 _cmask &= ~_mask;                                       \
 319                 _ptr[_this_unit] &= _mask;                              \
 320                 _ptr[_this_unit] |= _cmask;                             \
 321         } else                                                          \
 322                 _ptr[_this_unit] = (type) _v;                           \
 323 } while (0)
 324
 325 /*
 326  * bt_bitfield_write - write integer to a bitfield in native endianness
 327  * bt_bitfield_write_le - write integer to a bitfield in little endian
 328  * bt_bitfield_write_be - write integer to a bitfield in big endian
 329  */
 330
 331 #if (__BYTE_ORDER == __LITTLE_ENDIAN)
 332
 333 #define bt_bitfield_write(ptr, type, start, length, v)                  \
 334         _bt_bitfield_write_le(ptr, type, start, length, v)
 335
 336 #define bt_bitfield_write_le(ptr, type, start, length, v)               \
 337         _bt_bitfield_write_le(ptr, type, start, length, v)
 338
 339 #define bt_bitfield_write_be(ptr, type, start, length, v)               \
 340         _bt_bitfield_write_be(ptr, unsigned char, start, length, v)
 341
 342 #elif (__BYTE_ORDER == __BIG_ENDIAN)
 343
 344 #define bt_bitfield_write(ptr, type, start, length, v)                  \
 345         _bt_bitfield_write_be(ptr, type, start, length, v)
 346
 347 #define bt_bitfield_write_le(ptr, type, start, length, v)               \
 348         _bt_bitfield_write_le(ptr, unsigned char, start, length, v)
 349
 350 #define bt_bitfield_write_be(ptr, type, start, length, v)               \
 351         _bt_bitfield_write_be(ptr, type, start, length, v)
 352
 353 #else /* (__BYTE_ORDER == __PDP_ENDIAN) */
 354
 355 #error "Byte order not supported"
 356
 357 #endif
 358
 359 #define _bt_bitfield_read_le(ptr, type, start, length, vptr)            \
 360 do {                                                                    \
 361         __typeof__(*(vptr)) *_vptr = (vptr);                            \
 362         __typeof__(*_vptr) _v;                                          \
 363         type *_ptr = (void *) (ptr);                                    \
 364         unsigned long _start = (start), _length = (length);             \
 365         type _mask, _cmask;                                             \
 366         unsigned long _ts = sizeof(type) * CHAR_BIT; /* type size */    \
 367         unsigned long _start_unit, _end_unit, _this_unit;               \
 368         unsigned long _end, _cshift; /* _cshift is "complement shift" */ \
 369         bool _is_signed_type;                                           \
 370                                                                         \
 371         if (!_length) {                                                 \
 372                 *_vptr = 0;                                             \
 373                 break;                                                  \
 374         }                                                               \
 375                                                                         \
 376         _end = _start + _length;                                        \
 377         _start_unit = _start / _ts;                                     \
 378         _end_unit = (_end + (_ts - 1)) / _ts;                           \
 379                                                                         \
 380         _this_unit = _end_unit - 1;                                     \
 381         _BT_DIAG_PUSH                                                   \
 382         _BT_DIAG_IGNORE_TYPE_LIMITS                                     \
 383         _is_signed_type = _bt_is_signed_type(__typeof__(_v));           \
 384         _BT_DIAG_POP                                                    \
 385         if (_is_signed_type                                             \
 386             && (_ptr[_this_unit] & _bt_lshift((type) 1, (_end % _ts ? _end % _ts : _ts) - 1))) \
 387                 _v = ~(__typeof__(_v)) 0;                               \
 388         else                                                            \
 389                 _v = 0;                                                 \
 390         if (_start_unit == _end_unit - 1) {                             \
 391                 _cmask = _ptr[_this_unit];                              \
 392                 _cmask = _bt_rshift(_cmask, _start % _ts);              \
 393                 if ((_end - _start) % _ts) {                            \
 394                         _mask = _bt_make_mask(type, _end - _start);     \
 395                         _cmask &= _mask;                                \
 396                 }                                                       \
 397                 _bt_safe_lshift(_v, _end - _start);                     \
 398                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _cmask); \
 399                 *_vptr = _v;                                            \
 400                 break;                                                  \
 401         }                                                               \
 402         if (_end % _ts) {                                               \
 403                 _cshift = _end % _ts;                                   \
 404                 _mask = _bt_make_mask(type, _cshift);                   \
 405                 _cmask = _ptr[_this_unit];                              \
 406                 _cmask &= _mask;                                        \
 407                 _bt_safe_lshift(_v, _cshift);                           \
 408                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _cmask); \
 409                 _end -= _cshift;                                        \
 410                 _this_unit--;                                           \
 411         }                                                               \
 412         for (; (long) _this_unit >= (long) _start_unit + 1; _this_unit--) { \
 413                 _bt_safe_lshift(_v, _ts);                               \
 414                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _ptr[_this_unit]); \
 415                 _end -= _ts;                                            \
 416         }                                                               \
 417         if (_start % _ts) {                                             \
 418                 _mask = _bt_make_mask(type, _ts - (_start % _ts));      \
 419                 _cmask = _ptr[_this_unit];                              \
 420                 _cmask = _bt_rshift(_cmask, _start % _ts);              \
 421                 _cmask &= _mask;                                        \
 422                 _bt_safe_lshift(_v, _ts - (_start % _ts));              \
 423                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _cmask); \
 424         } else {                                                        \
 425                 _bt_safe_lshift(_v, _ts);                               \
 426                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _ptr[_this_unit]); \
 427         }                                                               \
 428         *_vptr = _v;                                                    \
 429 } while (0)
 430
 431 #define _bt_bitfield_read_be(ptr, type, start, length, vptr)            \
 432 do {                                                                    \
 433         __typeof__(*(vptr)) *_vptr = (vptr);                            \
 434         __typeof__(*_vptr) _v;                                          \
 435         type *_ptr = (void *) (ptr);                                    \
 436         unsigned long _start = (start), _length = (length);             \
 437         type _mask, _cmask;                                             \
 438         unsigned long _ts = sizeof(type) * CHAR_BIT; /* type size */    \
 439         unsigned long _start_unit, _end_unit, _this_unit;               \
 440         unsigned long _end, _cshift; /* _cshift is "complement shift" */ \
 441         bool _is_signed_type;                                           \
 442                                                                         \
 443         if (!_length) {                                                 \
 444                 *_vptr = 0;                                             \
 445                 break;                                                  \
 446         }                                                               \
 447                                                                         \
 448         _end = _start + _length;                                        \
 449         _start_unit = _start / _ts;                                     \
 450         _end_unit = (_end + (_ts - 1)) / _ts;                           \
 451                                                                         \
 452         _this_unit = _start_unit;                                       \
 453         _BT_DIAG_PUSH                                                   \
 454         _BT_DIAG_IGNORE_TYPE_LIMITS                                     \
 455         _is_signed_type = _bt_is_signed_type(__typeof__(_v));           \
 456         _BT_DIAG_POP                                                    \
 457         if (_is_signed_type                                             \
 458             && (_ptr[_this_unit] & _bt_lshift((type) 1, _ts - (_start % _ts) - 1))) \
 459                 _v = ~(__typeof__(_v)) 0;                               \
 460         else                                                            \
 461                 _v = 0;                                                 \
 462         if (_start_unit == _end_unit - 1) {                             \
 463                 _cmask = _ptr[_this_unit];                              \
 464                 _cmask = _bt_rshift(_cmask, (_ts - (_end % _ts)) % _ts); \
 465                 if ((_end - _start) % _ts) {                            \
 466                         _mask = _bt_make_mask(type, _end - _start);     \
 467                         _cmask &= _mask;                                \
 468                 }                                                       \
 469                 _bt_safe_lshift(_v, _end - _start);                     \
 470                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _cmask); \
 471                 *_vptr = _v;                                            \
 472                 break;                                                  \
 473         }                                                               \
 474         if (_start % _ts) {                                             \
 475                 _cshift = _start % _ts;                                 \
 476                 _mask = _bt_make_mask(type, _ts - _cshift);             \
 477                 _cmask = _ptr[_this_unit];                              \
 478                 _cmask &= _mask;                                        \
 479                 _bt_safe_lshift(_v, _ts - _cshift);                     \
 480                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _cmask); \
 481                 _start += _ts - _cshift;                                \
 482                 _this_unit++;                                           \
 483         }                                                               \
 484         for (; _this_unit < _end_unit - 1; _this_unit++) {              \
 485                 _bt_safe_lshift(_v, _ts);                               \
 486                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _ptr[_this_unit]); \
 487                 _start += _ts;                                          \
 488         }                                                               \
 489         if (_end % _ts) {                                               \
 490                 _mask = _bt_make_mask(type, _end % _ts);                \
 491                 _cmask = _ptr[_this_unit];                              \
 492                 _cmask = _bt_rshift(_cmask, _ts - (_end % _ts));        \
 493                 _cmask &= _mask;                                        \
 494                 _bt_safe_lshift(_v, _end % _ts);                        \
 495                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _cmask); \
 496         } else {                                                        \
 497                 _bt_safe_lshift(_v, _ts);                               \
 498                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _ptr[_this_unit]); \
 499         }                                                               \
 500         *_vptr = _v;                                                    \
 501 } while (0)
 502
 503 /*
 504  * bt_bitfield_read - read integer from a bitfield in native endianness
 505  * bt_bitfield_read_le - read integer from a bitfield in little endian
 506  * bt_bitfield_read_be - read integer from a bitfield in big endian
 507  */
 508
 509 #if (__BYTE_ORDER == __LITTLE_ENDIAN)
 510
 511 #define bt_bitfield_read(ptr, type, start, length, vptr)                \
 512         _bt_bitfield_read_le(ptr, type, start, length, vptr)
 513
 514 #define bt_bitfield_read_le(ptr, type, start, length, vptr)             \
 515         _bt_bitfield_read_le(ptr, type, start, length, vptr)
 516
 517 #define bt_bitfield_read_be(ptr, type, start, length, vptr)             \
 518         _bt_bitfield_read_be(ptr, unsigned char, start, length, vptr)
 519
 520 #elif (__BYTE_ORDER == __BIG_ENDIAN)
 521
 522 #define bt_bitfield_read(ptr, type, start, length, vptr)                \
 523         _bt_bitfield_read_be(ptr, type, start, length, vptr)
 524
 525 #define bt_bitfield_read_le(ptr, type, start, length, vptr)             \
 526         _bt_bitfield_read_le(ptr, unsigned char, start, length, vptr)
 527
 528 #define bt_bitfield_read_be(ptr, type, start, length, vptr)             \
 529         _bt_bitfield_read_be(ptr, type, start, length, vptr)
 530
 531 #else /* (__BYTE_ORDER == __PDP_ENDIAN) */
 532
 533 #error "Byte order not supported"
 534
 535 #endif
 536
 537 #endif /* _BABELTRACE_BITFIELD_H */