include/lttng/bitfield.h

   1 #ifndef _BABELTRACE_BITFIELD_H
   2 #define _BABELTRACE_BITFIELD_H
   3
   4 /*
   5  * Copyright 2010-2019 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   6  *
   7  * Permission is hereby granted, free of charge, to any person obtaining a copy
   8  * of this software and associated documentation files (the "Software"), to deal
   9  * in the Software without restriction, including without limitation the rights
  10  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  11  * copies of the Software, and to permit persons to whom the Software is
  12  * furnished to do so, subject to the following conditions:
  13  *
  14  * The above copyright notice and this permission notice shall be included in
  15  * all copies or substantial portions of the Software.
  16  *
  17  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  18  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  20  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  21  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  22  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  23  * SOFTWARE.
  24  */
  25
  26 #include <stdint.h>     /* C99 5.2.4.2 Numerical limits */
  27 #include <limits.h>     /* C99 5.2.4.2 Numerical limits */
  28 #include <stdbool.h>    /* C99 7.16 bool type */
  29 #include <lttng/ust-endian.h>   /* Non-standard BIG_ENDIAN, LITTLE_ENDIAN, BYTE_ORDER */
  30
  31 /*
  32  * This header strictly follows the C99 standard, except for use of the
  33  * compiler-specific __typeof__.
  34  */
  35
  36 /*
  37  * This bitfield header requires the compiler representation of signed
  38  * integers to be two's complement.
  39  */
  40 #if (-1 != ~0)
  41 #error "bitfield.h requires the compiler representation of signed integers to be two's complement."
  42 #endif
  43
  44 #define _bt_is_signed_type(type)        ((type) -1 < (type) 1)
  45
  46 /*
  47  * Produce a build-time error if the condition `cond` is non-zero.
  48  * Evaluates as a size_t expression.
  49  */
  50 #define _BT_BUILD_ASSERT(cond)                                  \
  51         sizeof(struct { int f:(2 * !!(cond) - 1); })
  52
  53 /*
  54  * Cast value `v` to an unsigned integer of the same size as `v`.
  55  */
  56 #define _bt_cast_value_to_unsigned(v)                                   \
  57         (sizeof(v) == sizeof(uint8_t) ? (uint8_t) (v) :                 \
  58         sizeof(v) == sizeof(uint16_t) ? (uint16_t) (v) :                \
  59         sizeof(v) == sizeof(uint32_t) ? (uint32_t) (v) :                \
  60         sizeof(v) == sizeof(uint64_t) ? (uint64_t) (v) :                \
  61         _BT_BUILD_ASSERT(sizeof(v) <= sizeof(uint64_t)))
  62
  63 /*
  64  * Cast value `v` to an unsigned integer type of the size of type `type`
  65  * *without* sign-extension.
  66  *
  67  * The unsigned cast ensures that we're not shifting a negative value,
  68  * which is undefined in C. However, this limits the maximum type size
  69  * of `type` to 64-bit. Generate a compile-time error if the size of
  70  * `type` is larger than 64-bit.
  71  */
  72 #define _bt_cast_value_to_unsigned_type(type, v)                        \
  73         (sizeof(type) == sizeof(uint8_t) ?                              \
  74                 (uint8_t) _bt_cast_value_to_unsigned(v) :               \
  75         sizeof(type) == sizeof(uint16_t) ?                              \
  76                 (uint16_t) _bt_cast_value_to_unsigned(v) :              \
  77         sizeof(type) == sizeof(uint32_t) ?                              \
  78                 (uint32_t) _bt_cast_value_to_unsigned(v) :              \
  79         sizeof(type) == sizeof(uint64_t) ?                              \
  80                 (uint64_t) _bt_cast_value_to_unsigned(v) :              \
  81         _BT_BUILD_ASSERT(sizeof(v) <= sizeof(uint64_t)))
  82
  83 /*
  84  * _bt_fill_mask evaluates to a "type" integer with all bits set.
  85  */
  86 #define _bt_fill_mask(type)     ((type) ~(type) 0)
  87
  88 /*
  89  * Left shift a value `v` of `shift` bits.
  90  *
  91  * The type of `v` can be signed or unsigned integer.
  92  * The value of `shift` must be less than the size of `v` (in bits),
  93  * otherwise the behavior is undefined.
  94  * Evaluates to the result of the shift operation.
  95  *
  96  * According to the C99 standard, left shift of a left hand-side signed
  97  * type is undefined if it has a negative value or if the result cannot
  98  * be represented in the result type. This bitfield header discards the
  99  * bits that are left-shifted beyond the result type representation,
 100  * which is the behavior of an unsigned type left shift operation.
 101  * Therefore, always perform left shift on an unsigned type.
 102  *
 103  * This macro should not be used if `shift` can be greater or equal than
 104  * the bitwidth of `v`. See `_bt_safe_lshift`.
 105  */
 106 #define _bt_lshift(v, shift)                                            \
 107         ((__typeof__(v)) (_bt_cast_value_to_unsigned(v) << (shift)))
 108
 109 /*
 110  * Generate a mask of type `type` with the `length` least significant bits
 111  * cleared, and the most significant bits set.
 112  */
 113 #define _bt_make_mask_complement(type, length)                          \
 114         _bt_lshift(_bt_fill_mask(type), length)
 115
 116 /*
 117  * Generate a mask of type `type` with the `length` least significant bits
 118  * set, and the most significant bits cleared.
 119  */
 120 #define _bt_make_mask(type, length)                                     \
 121         ((type) ~_bt_make_mask_complement(type, length))
 122
 123 /*
 124  * Right shift a value `v` of `shift` bits.
 125  *
 126  * The type of `v` can be signed or unsigned integer.
 127  * The value of `shift` must be less than the size of `v` (in bits),
 128  * otherwise the behavior is undefined.
 129  * Evaluates to the result of the shift operation.
 130  *
 131  * According to the C99 standard, right shift of a left hand-side signed
 132  * type which has a negative value is implementation defined. This
 133  * bitfield header relies on the right shift implementation carrying the
 134  * sign bit. If the compiler implementation has a different behavior,
 135  * emulate carrying the sign bit.
 136  *
 137  * This macro should not be used if `shift` can be greater or equal than
 138  * the bitwidth of `v`. See `_bt_safe_rshift`.
 139  */
 140 #if ((-1 >> 1) == -1)
 141 #define _bt_rshift(v, shift)    ((v) >> (shift))
 142 #else
 143 #define _bt_rshift(v, shift)                                            \
 144         ((__typeof__(v)) ((_bt_cast_value_to_unsigned(v) >> (shift)) |  \
 145                 ((v) < 0 ? _bt_make_mask_complement(__typeof__(v),      \
 146                         sizeof(v) * CHAR_BIT - (shift)) : 0)))
 147 #endif
 148
 149 /*
 150  * Right shift a signed or unsigned integer with `shift` value being an
 151  * arbitrary number of bits. `v` is modified by this macro. The shift
 152  * is transformed into a sequence of `_nr_partial_shifts` consecutive
 153  * shift operations, each of a number of bits smaller than the bitwidth
 154  * of `v`, ending with a shift of the number of left over bits.
 155  */
 156 #define _bt_safe_rshift(v, shift)                                       \
 157 do {                                                                    \
 158         unsigned long _nr_partial_shifts = (shift) / (sizeof(v) * CHAR_BIT - 1); \
 159         unsigned long _leftover_bits = (shift) % (sizeof(v) * CHAR_BIT - 1); \
 160                                                                         \
 161         for (; _nr_partial_shifts; _nr_partial_shifts--)                \
 162                 (v) = _bt_rshift(v, sizeof(v) * CHAR_BIT - 1);          \
 163         (v) = _bt_rshift(v, _leftover_bits);                            \
 164 } while (0)
 165
 166 /*
 167  * Left shift a signed or unsigned integer with `shift` value being an
 168  * arbitrary number of bits. `v` is modified by this macro. The shift
 169  * is transformed into a sequence of `_nr_partial_shifts` consecutive
 170  * shift operations, each of a number of bits smaller than the bitwidth
 171  * of `v`, ending with a shift of the number of left over bits.
 172  */
 173 #define _bt_safe_lshift(v, shift)                                       \
 174 do {                                                                    \
 175         unsigned long _nr_partial_shifts = (shift) / (sizeof(v) * CHAR_BIT - 1); \
 176         unsigned long _leftover_bits = (shift) % (sizeof(v) * CHAR_BIT - 1); \
 177                                                                         \
 178         for (; _nr_partial_shifts; _nr_partial_shifts--)                \
 179                 (v) = _bt_lshift(v, sizeof(v) * CHAR_BIT - 1);          \
 180         (v) = _bt_lshift(v, _leftover_bits);                            \
 181 } while (0)
 182
 183 /*
 184  * bt_bitfield_write - write integer to a bitfield in native endianness
 185  *
 186  * Save integer to the bitfield, which starts at the "start" bit, has "len"
 187  * bits.
 188  * The inside of a bitfield is from high bits to low bits.
 189  * Uses native endianness.
 190  * For unsigned "v", pad MSB with 0 if bitfield is larger than v.
 191  * For signed "v", sign-extend v if bitfield is larger than v.
 192  *
 193  * On little endian, bytes are placed from the less significant to the most
 194  * significant. Also, consecutive bitfields are placed from lower bits to higher
 195  * bits.
 196  *
 197  * On big endian, bytes are places from most significant to less significant.
 198  * Also, consecutive bitfields are placed from higher to lower bits.
 199  */
 200
 201 #define _bt_bitfield_write_le(ptr, type, start, length, v)              \
 202 do {                                                                    \
 203         __typeof__(v) _v = (v);                                 \
 204         type *_ptr = (void *) (ptr);                                    \
 205         unsigned long _start = (start), _length = (length);             \
 206         type _mask, _cmask;                                             \
 207         unsigned long _ts = sizeof(type) * CHAR_BIT; /* type size */    \
 208         unsigned long _start_unit, _end_unit, _this_unit;               \
 209         unsigned long _end, _cshift; /* _cshift is "complement shift" */ \
 210                                                                         \
 211         if (!_length)                                                   \
 212                 break;                                                  \
 213                                                                         \
 214         _end = _start + _length;                                        \
 215         _start_unit = _start / _ts;                                     \
 216         _end_unit = (_end + (_ts - 1)) / _ts;                           \
 217                                                                         \
 218         /* Trim v high bits */                                          \
 219         if (_length < sizeof(_v) * CHAR_BIT)                            \
 220                 _v &= _bt_make_mask(__typeof__(_v), _length);           \
 221                                                                         \
 222         /* We can now append v with a simple "or", shift it piece-wise */ \
 223         _this_unit = _start_unit;                                       \
 224         if (_start_unit == _end_unit - 1) {                             \
 225                 _mask = _bt_make_mask(type, _start % _ts);              \
 226                 if (_end % _ts)                                         \
 227                         _mask |= _bt_make_mask_complement(type, _end % _ts); \
 228                 _cmask = _bt_lshift((type) (_v), _start % _ts);         \
 229                 _cmask &= ~_mask;                                       \
 230                 _ptr[_this_unit] &= _mask;                              \
 231                 _ptr[_this_unit] |= _cmask;                             \
 232                 break;                                                  \
 233         }                                                               \
 234         if (_start % _ts) {                                             \
 235                 _cshift = _start % _ts;                                 \
 236                 _mask = _bt_make_mask(type, _cshift);                   \
 237                 _cmask = _bt_lshift((type) (_v), _cshift);              \
 238                 _cmask &= ~_mask;                                       \
 239                 _ptr[_this_unit] &= _mask;                              \
 240                 _ptr[_this_unit] |= _cmask;                             \
 241                 _bt_safe_rshift(_v, _ts - _cshift);                     \
 242                 _start += _ts - _cshift;                                \
 243                 _this_unit++;                                           \
 244         }                                                               \
 245         for (; _this_unit < _end_unit - 1; _this_unit++) {              \
 246                 _ptr[_this_unit] = (type) _v;                           \
 247                 _bt_safe_rshift(_v, _ts);                               \
 248                 _start += _ts;                                          \
 249         }                                                               \
 250         if (_end % _ts) {                                               \
 251                 _mask = _bt_make_mask_complement(type, _end % _ts);     \
 252                 _cmask = (type) _v;                                     \
 253                 _cmask &= ~_mask;                                       \
 254                 _ptr[_this_unit] &= _mask;                              \
 255                 _ptr[_this_unit] |= _cmask;                             \
 256         } else                                                          \
 257                 _ptr[_this_unit] = (type) _v;                           \
 258 } while (0)
 259
 260 #define _bt_bitfield_write_be(ptr, type, start, length, v)              \
 261 do {                                                                    \
 262         __typeof__(v) _v = (v);                                         \
 263         type *_ptr = (void *) (ptr);                                    \
 264         unsigned long _start = (start), _length = (length);             \
 265         type _mask, _cmask;                                             \
 266         unsigned long _ts = sizeof(type) * CHAR_BIT; /* type size */    \
 267         unsigned long _start_unit, _end_unit, _this_unit;               \
 268         unsigned long _end, _cshift; /* _cshift is "complement shift" */ \
 269                                                                         \
 270         if (!_length)                                                   \
 271                 break;                                                  \
 272                                                                         \
 273         _end = _start + _length;                                        \
 274         _start_unit = _start / _ts;                                     \
 275         _end_unit = (_end + (_ts - 1)) / _ts;                           \
 276                                                                         \
 277         /* Trim v high bits */                                          \
 278         if (_length < sizeof(_v) * CHAR_BIT)                            \
 279                 _v &= _bt_make_mask(__typeof__(_v), _length);           \
 280                                                                         \
 281         /* We can now append v with a simple "or", shift it piece-wise */ \
 282         _this_unit = _end_unit - 1;                                     \
 283         if (_start_unit == _end_unit - 1) {                             \
 284                 _mask = _bt_make_mask(type, (_ts - (_end % _ts)) % _ts); \
 285                 if (_start % _ts)                                       \
 286                         _mask |= _bt_make_mask_complement(type, _ts - (_start % _ts)); \
 287                 _cmask = _bt_lshift((type) (_v), (_ts - (_end % _ts)) % _ts); \
 288                 _cmask &= ~_mask;                                       \
 289                 _ptr[_this_unit] &= _mask;                              \
 290                 _ptr[_this_unit] |= _cmask;                             \
 291                 break;                                                  \
 292         }                                                               \
 293         if (_end % _ts) {                                               \
 294                 _cshift = _end % _ts;                                   \
 295                 _mask = _bt_make_mask(type, _ts - _cshift);             \
 296                 _cmask = _bt_lshift((type) (_v), _ts - _cshift);        \
 297                 _cmask &= ~_mask;                                       \
 298                 _ptr[_this_unit] &= _mask;                              \
 299                 _ptr[_this_unit] |= _cmask;                             \
 300                 _bt_safe_rshift(_v, _cshift);                           \
 301                 _end -= _cshift;                                        \
 302                 _this_unit--;                                           \
 303         }                                                               \
 304         for (; (long) _this_unit >= (long) _start_unit + 1; _this_unit--) { \
 305                 _ptr[_this_unit] = (type) _v;                           \
 306                 _bt_safe_rshift(_v, _ts);                               \
 307                 _end -= _ts;                                            \
 308         }                                                               \
 309         if (_start % _ts) {                                             \
 310                 _mask = _bt_make_mask_complement(type, _ts - (_start % _ts)); \
 311                 _cmask = (type) _v;                                     \
 312                 _cmask &= ~_mask;                                       \
 313                 _ptr[_this_unit] &= _mask;                              \
 314                 _ptr[_this_unit] |= _cmask;                             \
 315         } else                                                          \
 316                 _ptr[_this_unit] = (type) _v;                           \
 317 } while (0)
 318
 319 /*
 320  * bt_bitfield_write - write integer to a bitfield in native endianness
 321  * bt_bitfield_write_le - write integer to a bitfield in little endian
 322  * bt_bitfield_write_be - write integer to a bitfield in big endian
 323  */
 324
 325 #if (BYTE_ORDER == LITTLE_ENDIAN)
 326
 327 #define bt_bitfield_write(ptr, type, start, length, v)                  \
 328         _bt_bitfield_write_le(ptr, type, start, length, v)
 329
 330 #define bt_bitfield_write_le(ptr, type, start, length, v)               \
 331         _bt_bitfield_write_le(ptr, type, start, length, v)
 332
 333 #define bt_bitfield_write_be(ptr, type, start, length, v)               \
 334         _bt_bitfield_write_be(ptr, unsigned char, start, length, v)
 335
 336 #elif (BYTE_ORDER == BIG_ENDIAN)
 337
 338 #define bt_bitfield_write(ptr, type, start, length, v)                  \
 339         _bt_bitfield_write_be(ptr, type, start, length, v)
 340
 341 #define bt_bitfield_write_le(ptr, type, start, length, v)               \
 342         _bt_bitfield_write_le(ptr, unsigned char, start, length, v)
 343
 344 #define bt_bitfield_write_be(ptr, type, start, length, v)               \
 345         _bt_bitfield_write_be(ptr, type, start, length, v)
 346
 347 #else /* (BYTE_ORDER == PDP_ENDIAN) */
 348
 349 #error "Byte order not supported"
 350
 351 #endif
 352
 353 #define _bt_bitfield_read_le(ptr, type, start, length, vptr)            \
 354 do {                                                                    \
 355         __typeof__(*(vptr)) *_vptr = (vptr);                            \
 356         __typeof__(*_vptr) _v;                                          \
 357         type *_ptr = (void *) (ptr);                                    \
 358         unsigned long _start = (start), _length = (length);             \
 359         type _mask, _cmask;                                             \
 360         unsigned long _ts = sizeof(type) * CHAR_BIT; /* type size */    \
 361         unsigned long _start_unit, _end_unit, _this_unit;               \
 362         unsigned long _end, _cshift; /* _cshift is "complement shift" */ \
 363                                                                         \
 364         if (!_length) {                                                 \
 365                 *_vptr = 0;                                             \
 366                 break;                                                  \
 367         }                                                               \
 368                                                                         \
 369         _end = _start + _length;                                        \
 370         _start_unit = _start / _ts;                                     \
 371         _end_unit = (_end + (_ts - 1)) / _ts;                           \
 372                                                                         \
 373         _this_unit = _end_unit - 1;                                     \
 374         if (_bt_is_signed_type(__typeof__(_v))                          \
 375             && (_ptr[_this_unit] & _bt_lshift((type) 1, (_end % _ts ? _end % _ts : _ts) - 1))) \
 376                 _v = ~(__typeof__(_v)) 0;                               \
 377         else                                                            \
 378                 _v = 0;                                                 \
 379         if (_start_unit == _end_unit - 1) {                             \
 380                 _cmask = _ptr[_this_unit];                              \
 381                 _cmask = _bt_rshift(_cmask, _start % _ts);              \
 382                 if ((_end - _start) % _ts) {                            \
 383                         _mask = _bt_make_mask(type, _end - _start);     \
 384                         _cmask &= _mask;                                \
 385                 }                                                       \
 386                 _bt_safe_lshift(_v, _end - _start);                     \
 387                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _cmask); \
 388                 *_vptr = _v;                                            \
 389                 break;                                                  \
 390         }                                                               \
 391         if (_end % _ts) {                                               \
 392                 _cshift = _end % _ts;                                   \
 393                 _mask = _bt_make_mask(type, _cshift);                   \
 394                 _cmask = _ptr[_this_unit];                              \
 395                 _cmask &= _mask;                                        \
 396                 _bt_safe_lshift(_v, _cshift);                           \
 397                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _cmask); \
 398                 _end -= _cshift;                                        \
 399                 _this_unit--;                                           \
 400         }                                                               \
 401         for (; (long) _this_unit >= (long) _start_unit + 1; _this_unit--) { \
 402                 _bt_safe_lshift(_v, _ts);                               \
 403                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _ptr[_this_unit]); \
 404                 _end -= _ts;                                            \
 405         }                                                               \
 406         if (_start % _ts) {                                             \
 407                 _mask = _bt_make_mask(type, _ts - (_start % _ts));      \
 408                 _cmask = _ptr[_this_unit];                              \
 409                 _cmask = _bt_rshift(_cmask, _start % _ts);              \
 410                 _cmask &= _mask;                                        \
 411                 _bt_safe_lshift(_v, _ts - (_start % _ts));              \
 412                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _cmask); \
 413         } else {                                                        \
 414                 _bt_safe_lshift(_v, _ts);                               \
 415                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _ptr[_this_unit]); \
 416         }                                                               \
 417         *_vptr = _v;                                                    \
 418 } while (0)
 419
 420 #define _bt_bitfield_read_be(ptr, type, start, length, vptr)            \
 421 do {                                                                    \
 422         __typeof__(*(vptr)) *_vptr = (vptr);                            \
 423         __typeof__(*_vptr) _v;                                          \
 424         type *_ptr = (void *) (ptr);                                    \
 425         unsigned long _start = (start), _length = (length);             \
 426         type _mask, _cmask;                                             \
 427         unsigned long _ts = sizeof(type) * CHAR_BIT; /* type size */    \
 428         unsigned long _start_unit, _end_unit, _this_unit;               \
 429         unsigned long _end, _cshift; /* _cshift is "complement shift" */ \
 430                                                                         \
 431         if (!_length) {                                                 \
 432                 *_vptr = 0;                                             \
 433                 break;                                                  \
 434         }                                                               \
 435                                                                         \
 436         _end = _start + _length;                                        \
 437         _start_unit = _start / _ts;                                     \
 438         _end_unit = (_end + (_ts - 1)) / _ts;                           \
 439                                                                         \
 440         _this_unit = _start_unit;                                       \
 441         if (_bt_is_signed_type(__typeof__(_v))                          \
 442             && (_ptr[_this_unit] & _bt_lshift((type) 1, _ts - (_start % _ts) - 1))) \
 443                 _v = ~(__typeof__(_v)) 0;                               \
 444         else                                                            \
 445                 _v = 0;                                                 \
 446         if (_start_unit == _end_unit - 1) {                             \
 447                 _cmask = _ptr[_this_unit];                              \
 448                 _cmask = _bt_rshift(_cmask, (_ts - (_end % _ts)) % _ts); \
 449                 if ((_end - _start) % _ts) {                            \
 450                         _mask = _bt_make_mask(type, _end - _start);     \
 451                         _cmask &= _mask;                                \
 452                 }                                                       \
 453                 _bt_safe_lshift(_v, _end - _start);                     \
 454                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _cmask); \
 455                 *_vptr = _v;                                            \
 456                 break;                                                  \
 457         }                                                               \
 458         if (_start % _ts) {                                             \
 459                 _cshift = _start % _ts;                                 \
 460                 _mask = _bt_make_mask(type, _ts - _cshift);             \
 461                 _cmask = _ptr[_this_unit];                              \
 462                 _cmask &= _mask;                                        \
 463                 _bt_safe_lshift(_v, _ts - _cshift);                     \
 464                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _cmask); \
 465                 _start += _ts - _cshift;                                \
 466                 _this_unit++;                                           \
 467         }                                                               \
 468         for (; _this_unit < _end_unit - 1; _this_unit++) {              \
 469                 _bt_safe_lshift(_v, _ts);                               \
 470                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _ptr[_this_unit]); \
 471                 _start += _ts;                                          \
 472         }                                                               \
 473         if (_end % _ts) {                                               \
 474                 _mask = _bt_make_mask(type, _end % _ts);                \
 475                 _cmask = _ptr[_this_unit];                              \
 476                 _cmask = _bt_rshift(_cmask, _ts - (_end % _ts));        \
 477                 _cmask &= _mask;                                        \
 478                 _bt_safe_lshift(_v, _end % _ts);                        \
 479                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _cmask); \
 480         } else {                                                        \
 481                 _bt_safe_lshift(_v, _ts);                               \
 482                 _v |= _bt_cast_value_to_unsigned_type(__typeof__(_v), _ptr[_this_unit]); \
 483         }                                                               \
 484         *_vptr = _v;                                                    \
 485 } while (0)
 486
 487 /*
 488  * bt_bitfield_read - read integer from a bitfield in native endianness
 489  * bt_bitfield_read_le - read integer from a bitfield in little endian
 490  * bt_bitfield_read_be - read integer from a bitfield in big endian
 491  */
 492
 493 #if (BYTE_ORDER == LITTLE_ENDIAN)
 494
 495 #define bt_bitfield_read(ptr, type, start, length, vptr)                \
 496         _bt_bitfield_read_le(ptr, type, start, length, vptr)
 497
 498 #define bt_bitfield_read_le(ptr, type, start, length, vptr)             \
 499         _bt_bitfield_read_le(ptr, type, start, length, vptr)
 500
 501 #define bt_bitfield_read_be(ptr, type, start, length, vptr)             \
 502         _bt_bitfield_read_be(ptr, unsigned char, start, length, vptr)
 503
 504 #elif (BYTE_ORDER == BIG_ENDIAN)
 505
 506 #define bt_bitfield_read(ptr, type, start, length, vptr)                \
 507         _bt_bitfield_read_be(ptr, type, start, length, vptr)
 508
 509 #define bt_bitfield_read_le(ptr, type, start, length, vptr)             \
 510         _bt_bitfield_read_le(ptr, unsigned char, start, length, vptr)
 511
 512 #define bt_bitfield_read_be(ptr, type, start, length, vptr)             \
 513         _bt_bitfield_read_be(ptr, type, start, length, vptr)
 514
 515 #else /* (BYTE_ORDER == PDP_ENDIAN) */
 516
 517 #error "Byte order not supported"
 518
 519 #endif
 520
 521 #endif /* _BABELTRACE_BITFIELD_H */