include/obstack.h

   1 /* obstack.h - object stack macros
   2    Copyright (C) 1988-2021 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 /* Summary:
  20
  21    All the apparent functions defined here are macros. The idea
  22    is that you would use these pre-tested macros to solve a
  23    very specific set of problems, and they would run fast.
  24    Caution: no side-effects in arguments please!! They may be
  25    evaluated MANY times!!
  26
  27    These macros operate a stack of objects.  Each object starts life
  28    small, and may grow to maturity.  (Consider building a word syllable
  29    by syllable.)  An object can move while it is growing.  Once it has
  30    been "finished" it never changes address again.  So the "top of the
  31    stack" is typically an immature growing object, while the rest of the
  32    stack is of mature, fixed size and fixed address objects.
  33
  34    These routines grab large chunks of memory, using a function you
  35    supply, called 'obstack_chunk_alloc'.  On occasion, they free chunks,
  36    by calling 'obstack_chunk_free'.  You must define them and declare
  37    them before using any obstack macros.
  38
  39    Each independent stack is represented by a 'struct obstack'.
  40    Each of the obstack macros expects a pointer to such a structure
  41    as the first argument.
  42
  43    One motivation for this package is the problem of growing char strings
  44    in symbol tables.  Unless you are "fascist pig with a read-only mind"
  45    --Gosper's immortal quote from HAKMEM item 154, out of context--you
  46    would not like to put any arbitrary upper limit on the length of your
  47    symbols.
  48
  49    In practice this often means you will build many short symbols and a
  50    few long symbols.  At the time you are reading a symbol you don't know
  51    how long it is.  One traditional method is to read a symbol into a
  52    buffer, realloc()ating the buffer every time you try to read a symbol
  53    that is longer than the buffer.  This is beaut, but you still will
  54    want to copy the symbol from the buffer to a more permanent
  55    symbol-table entry say about half the time.
  56
  57    With obstacks, you can work differently.  Use one obstack for all symbol
  58    names.  As you read a symbol, grow the name in the obstack gradually.
  59    When the name is complete, finalize it.  Then, if the symbol exists already,
  60    free the newly read name.
  61
  62    The way we do this is to take a large chunk, allocating memory from
  63    low addresses.  When you want to build a symbol in the chunk you just
  64    add chars above the current "high water mark" in the chunk.  When you
  65    have finished adding chars, because you got to the end of the symbol,
  66    you know how long the chars are, and you can create a new object.
  67    Mostly the chars will not burst over the highest address of the chunk,
  68    because you would typically expect a chunk to be (say) 100 times as
  69    long as an average object.
  70
  71    In case that isn't clear, when we have enough chars to make up
  72    the object, THEY ARE ALREADY CONTIGUOUS IN THE CHUNK (guaranteed)
  73    so we just point to it where it lies.  No moving of chars is
  74    needed and this is the second win: potentially long strings need
  75    never be explicitly shuffled. Once an object is formed, it does not
  76    change its address during its lifetime.
  77
  78    When the chars burst over a chunk boundary, we allocate a larger
  79    chunk, and then copy the partly formed object from the end of the old
  80    chunk to the beginning of the new larger chunk.  We then carry on
  81    accreting characters to the end of the object as we normally would.
  82
  83    A special macro is provided to add a single char at a time to a
  84    growing object.  This allows the use of register variables, which
  85    break the ordinary 'growth' macro.
  86
  87    Summary:
  88         We allocate large chunks.
  89         We carve out one object at a time from the current chunk.
  90         Once carved, an object never moves.
  91         We are free to append data of any size to the currently
  92           growing object.
  93         Exactly one object is growing in an obstack at any one time.
  94         You can run one obstack per control block.
  95         You may have as many control blocks as you dare.
  96         Because of the way we do it, you can "unwind" an obstack
  97           back to a previous state. (You may remove objects much
  98           as you would with a stack.)
  99  */
 100
 101
 102 /* Don't do the contents of this file more than once.  */
 103
 104 #ifndef _OBSTACK_H
 105 #define _OBSTACK_H 1
 106
 107 /* We need the type of a pointer subtraction.  If __PTRDIFF_TYPE__ is
 108    defined, as with GNU C, use that; that way we don't pollute the
 109    namespace with <stddef.h>'s symbols.  Otherwise, include <stddef.h>
 110    and use ptrdiff_t.  */
 111
 112 #ifdef __PTRDIFF_TYPE__
 113 # define PTR_INT_TYPE __PTRDIFF_TYPE__
 114 #else
 115 # include <stddef.h>
 116 # define PTR_INT_TYPE ptrdiff_t
 117 #endif
 118
 119 /* If B is the base of an object addressed by P, return the result of
 120    aligning P to the next multiple of A + 1.  B and P must be of type
 121    char *.  A + 1 must be a power of 2.  */
 122
 123 #define __BPTR_ALIGN(B, P, A) ((B) + (((P) - (B) + (A)) & ~(A)))
 124
 125 /* Similar to _BPTR_ALIGN (B, P, A), except optimize the common case
 126    where pointers can be converted to integers, aligned as integers,
 127    and converted back again.  If PTR_INT_TYPE is narrower than a
 128    pointer (e.g., the AS/400), play it safe and compute the alignment
 129    relative to B.  Otherwise, use the faster strategy of computing the
 130    alignment relative to 0.  */
 131
 132 #define __PTR_ALIGN(B, P, A)                                                  \
 133   __BPTR_ALIGN (sizeof (PTR_INT_TYPE) < sizeof (void *) ? (B) : (char *) 0, \
 134                 P, A)
 135
 136 #include <string.h>
 137
 138 #ifndef __attribute_pure__
 139 # define __attribute_pure__ _GL_ATTRIBUTE_PURE
 140 #endif
 141
 142 #ifdef __cplusplus
 143 extern "C" {
 144 #endif
 145
 146 struct _obstack_chunk           /* Lives at front of each chunk. */
 147 {
 148   char *limit;                  /* 1 past end of this chunk */
 149   struct _obstack_chunk *prev;  /* address of prior chunk or NULL */
 150   char contents[4];             /* objects begin here */
 151 };
 152
 153 struct obstack          /* control current object in current chunk */
 154 {
 155   long chunk_size;              /* preferred size to allocate chunks in */
 156   struct _obstack_chunk *chunk; /* address of current struct obstack_chunk */
 157   char *object_base;            /* address of object we are building */
 158   char *next_free;              /* where to add next char to current object */
 159   char *chunk_limit;            /* address of char after current chunk */
 160   union
 161   {
 162     PTR_INT_TYPE tempint;
 163     void *tempptr;
 164   } temp;                       /* Temporary for some macros.  */
 165   int alignment_mask;           /* Mask of alignment for each object. */
 166   /* These prototypes vary based on 'use_extra_arg', and we use
 167      casts to the prototypeless function type in all assignments,
 168      but having prototypes here quiets -Wstrict-prototypes.  */
 169   struct _obstack_chunk *(*chunkfun) (void *, long);
 170   void (*freefun) (void *, struct _obstack_chunk *);
 171   void *extra_arg;              /* first arg for chunk alloc/dealloc funcs */
 172   unsigned use_extra_arg : 1;     /* chunk alloc/dealloc funcs take extra arg */
 173   unsigned maybe_empty_object : 1; /* There is a possibility that the current
 174                                       chunk contains a zero-length object.  This
 175                                       prevents freeing the chunk if we allocate
 176                                       a bigger chunk to replace it. */
 177   unsigned alloc_failed : 1;      /* No longer used, as we now call the failed
 178                                      handler on error, but retained for binary
 179                                      compatibility.  */
 180 };
 181
 182 /* Declare the external functions we use; they are in obstack.c.  */
 183
 184 extern void _obstack_newchunk (struct obstack *, int);
 185 extern int _obstack_begin (struct obstack *, int, int,
 186                            void *(*)(long), void (*)(void *));
 187 extern int _obstack_begin_1 (struct obstack *, int, int,
 188                              void *(*)(void *, long),
 189                              void (*)(void *, void *), void *);
 190 extern int _obstack_memory_used (struct obstack *) __attribute_pure__;
 191
 192 /* The default name of the function for freeing a chunk is 'obstack_free',
 193    but gnulib users can override this by defining '__obstack_free'.  */
 194 #ifndef __obstack_free
 195 # define __obstack_free obstack_free
 196 #endif
 197 extern void __obstack_free (struct obstack *, void *);
 198
 199
 200 /* Error handler called when 'obstack_chunk_alloc' failed to allocate
 201    more memory.  This can be set to a user defined function which
 202    should either abort gracefully or use longjump - but shouldn't
 203    return.  The default action is to print a message and abort.  */
 204 extern void (*obstack_alloc_failed_handler) (void);
 205
 206 /* Exit value used when 'print_and_abort' is used.  */
 207 extern int obstack_exit_failure;
 208
 209 /* Pointer to beginning of object being allocated or to be allocated next.
 210    Note that this might not be the final address of the object
 211    because a new chunk might be needed to hold the final size.  */
 212
 213 #define obstack_base(h) ((void *) (h)->object_base)
 214
 215 /* Size for allocating ordinary chunks.  */
 216
 217 #define obstack_chunk_size(h) ((h)->chunk_size)
 218
 219 /* Pointer to next byte not yet allocated in current chunk.  */
 220
 221 #define obstack_next_free(h)    ((h)->next_free)
 222
 223 /* Mask specifying low bits that should be clear in address of an object.  */
 224
 225 #define obstack_alignment_mask(h) ((h)->alignment_mask)
 226
 227 /* To prevent prototype warnings provide complete argument list.  */
 228 #define obstack_init(h)                                                       \
 229   _obstack_begin ((h), 0, 0,                                                  \
 230                   (void *(*)(long))obstack_chunk_alloc,                       \
 231                   (void (*)(void *))obstack_chunk_free)
 232
 233 #define obstack_begin(h, size)                                                \
 234   _obstack_begin ((h), (size), 0,                                             \
 235                   (void *(*)(long))obstack_chunk_alloc,                       \
 236                   (void (*)(void *))obstack_chunk_free)
 237
 238 #define obstack_specify_allocation(h, size, alignment, chunkfun, freefun)  \
 239   _obstack_begin ((h), (size), (alignment),                                   \
 240                   (void *(*)(long))(chunkfun),                                \
 241                   (void (*)(void *))(freefun))
 242
 243 #define obstack_specify_allocation_with_arg(h, size, alignment, chunkfun, freefun, arg) \
 244   _obstack_begin_1 ((h), (size), (alignment),                                 \
 245                     (void *(*)(void *, long))(chunkfun),                      \
 246                     (void (*)(void *, void *))(freefun), (arg))
 247
 248 #define obstack_chunkfun(h, newchunkfun) \
 249   ((h)->chunkfun = (struct _obstack_chunk *(*)(void *, long))(newchunkfun))
 250
 251 #define obstack_freefun(h, newfreefun) \
 252   ((h)->freefun = (void (*)(void *, struct _obstack_chunk *))(newfreefun))
 253
 254 #define obstack_1grow_fast(h, achar) (*((h)->next_free)++ = (achar))
 255
 256 #define obstack_blank_fast(h, n) ((h)->next_free += (n))
 257
 258 #define obstack_memory_used(h) _obstack_memory_used (h)
 259
 260 #if defined __GNUC__
 261 # if ! (2 < __GNUC__ + (8 <= __GNUC_MINOR__))
 262 #  define __extension__
 263 # endif
 264
 265 /* For GNU C, if not -traditional,
 266    we can define these macros to compute all args only once
 267    without using a global variable.
 268    Also, we can avoid using the 'temp' slot, to make faster code.  */
 269
 270 # define obstack_object_size(OBSTACK)                                         \
 271   __extension__                                                               \
 272     ({ struct obstack const *__o = (OBSTACK);                                 \
 273        (unsigned) (__o->next_free - __o->object_base); })
 274
 275 # define obstack_room(OBSTACK)                                                \
 276   __extension__                                                               \
 277     ({ struct obstack const *__o = (OBSTACK);                                 \
 278        (unsigned) (__o->chunk_limit - __o->next_free); })
 279
 280 # define obstack_make_room(OBSTACK, length)                                   \
 281   __extension__                                                               \
 282     ({ struct obstack *__o = (OBSTACK);                                       \
 283        int __len = (length);                                                  \
 284        if (__o->chunk_limit - __o->next_free < __len)                         \
 285          _obstack_newchunk (__o, __len);                                      \
 286        (void) 0; })
 287
 288 # define obstack_empty_p(OBSTACK)                                             \
 289   __extension__                                                               \
 290     ({ struct obstack const *__o = (OBSTACK);                                 \
 291        (__o->chunk->prev == 0                                                 \
 292         && __o->next_free == __PTR_ALIGN ((char *) __o->chunk,                \
 293                                           __o->chunk->contents,               \
 294                                           __o->alignment_mask)); })
 295
 296 # define obstack_grow(OBSTACK, where, length)                                 \
 297   __extension__                                                               \
 298     ({ struct obstack *__o = (OBSTACK);                                       \
 299        int __len = (length);                                                  \
 300        if (__o->next_free + __len > __o->chunk_limit)                         \
 301          _obstack_newchunk (__o, __len);                                      \
 302        memcpy (__o->next_free, where, __len);                                 \
 303        __o->next_free += __len;                                               \
 304        (void) 0; })
 305
 306 # define obstack_grow0(OBSTACK, where, length)                                \
 307   __extension__                                                               \
 308     ({ struct obstack *__o = (OBSTACK);                                       \
 309        int __len = (length);                                                  \
 310        if (__o->next_free + __len + 1 > __o->chunk_limit)                     \
 311          _obstack_newchunk (__o, __len + 1);                                  \
 312        memcpy (__o->next_free, where, __len);                                 \
 313        __o->next_free += __len;                                               \
 314        *(__o->next_free)++ = 0;                                               \
 315        (void) 0; })
 316
 317 # define obstack_1grow(OBSTACK, datum)                                        \
 318   __extension__                                                               \
 319     ({ struct obstack *__o = (OBSTACK);                                       \
 320        if (__o->next_free + 1 > __o->chunk_limit)                             \
 321          _obstack_newchunk (__o, 1);                                          \
 322        obstack_1grow_fast (__o, datum);                                       \
 323        (void) 0; })
 324
 325 /* These assume that the obstack alignment is good enough for pointers
 326    or ints, and that the data added so far to the current object
 327    shares that much alignment.  */
 328
 329 # define obstack_ptr_grow(OBSTACK, datum)                                     \
 330   __extension__                                                               \
 331     ({ struct obstack *__o = (OBSTACK);                                       \
 332        if (__o->next_free + sizeof (void *) > __o->chunk_limit)               \
 333          _obstack_newchunk (__o, sizeof (void *));                            \
 334        obstack_ptr_grow_fast (__o, datum); })                                 \
 335
 336 # define obstack_int_grow(OBSTACK, datum)                                     \
 337   __extension__                                                               \
 338     ({ struct obstack *__o = (OBSTACK);                                       \
 339        if (__o->next_free + sizeof (int) > __o->chunk_limit)                  \
 340          _obstack_newchunk (__o, sizeof (int));                               \
 341        obstack_int_grow_fast (__o, datum); })
 342
 343 # define obstack_ptr_grow_fast(OBSTACK, aptr)                                 \
 344   __extension__                                                               \
 345     ({ struct obstack *__o1 = (OBSTACK);                                      \
 346        void *__p1 = __o1->next_free;                                          \
 347        *(const void **) __p1 = (aptr);                                        \
 348        __o1->next_free += sizeof (const void *);                              \
 349        (void) 0; })
 350
 351 # define obstack_int_grow_fast(OBSTACK, aint)                                 \
 352   __extension__                                                               \
 353     ({ struct obstack *__o1 = (OBSTACK);                                      \
 354        void *__p1 = __o1->next_free;                                          \
 355        *(int *) __p1 = (aint);                                                \
 356        __o1->next_free += sizeof (int);                                       \
 357        (void) 0; })
 358
 359 # define obstack_blank(OBSTACK, length)                                       \
 360   __extension__                                                               \
 361     ({ struct obstack *__o = (OBSTACK);                                       \
 362        int __len = (length);                                                  \
 363        if (__o->chunk_limit - __o->next_free < __len)                         \
 364          _obstack_newchunk (__o, __len);                                      \
 365        obstack_blank_fast (__o, __len);                                       \
 366        (void) 0; })
 367
 368 # define obstack_alloc(OBSTACK, length)                                       \
 369   __extension__                                                               \
 370     ({ struct obstack *__h = (OBSTACK);                                       \
 371        obstack_blank (__h, (length));                                         \
 372        obstack_finish (__h); })
 373
 374 # define obstack_copy(OBSTACK, where, length)                                 \
 375   __extension__                                                               \
 376     ({ struct obstack *__h = (OBSTACK);                                       \
 377        obstack_grow (__h, (where), (length));                                 \
 378        obstack_finish (__h); })
 379
 380 # define obstack_copy0(OBSTACK, where, length)                                \
 381   __extension__                                                               \
 382     ({ struct obstack *__h = (OBSTACK);                                       \
 383        obstack_grow0 (__h, (where), (length));                                \
 384        obstack_finish (__h); })
 385
 386 /* The local variable is named __o1 to avoid a name conflict
 387    when obstack_blank is called.  */
 388 # define obstack_finish(OBSTACK)                                              \
 389   __extension__                                                               \
 390     ({ struct obstack *__o1 = (OBSTACK);                                      \
 391        void *__value = (void *) __o1->object_base;                            \
 392        if (__o1->next_free == __value)                                        \
 393          __o1->maybe_empty_object = 1;                                        \
 394        __o1->next_free                                                        \
 395          = __PTR_ALIGN (__o1->object_base, __o1->next_free,                   \
 396                         __o1->alignment_mask);                                \
 397        if (__o1->next_free - (char *) __o1->chunk                             \
 398            > __o1->chunk_limit - (char *) __o1->chunk)                        \
 399          __o1->next_free = __o1->chunk_limit;                                 \
 400        __o1->object_base = __o1->next_free;                                   \
 401        __value; })
 402
 403 # define obstack_free(OBSTACK, OBJ)                                           \
 404   __extension__                                                               \
 405     ({ struct obstack *__o = (OBSTACK);                                       \
 406        void *__obj = (OBJ);                                                   \
 407        if (__obj > (void *) __o->chunk && __obj < (void *) __o->chunk_limit)  \
 408          __o->next_free = __o->object_base = (char *) __obj;                  \
 409        else (__obstack_free) (__o, __obj); })
 410
 411 #else /* not __GNUC__ */
 412
 413 # define obstack_object_size(h) \
 414   (unsigned) ((h)->next_free - (h)->object_base)
 415
 416 # define obstack_room(h)                                                      \
 417   (unsigned) ((h)->chunk_limit - (h)->next_free)
 418
 419 # define obstack_empty_p(h) \
 420   ((h)->chunk->prev == 0                                                      \
 421    && (h)->next_free == __PTR_ALIGN ((char *) (h)->chunk,                     \
 422                                      (h)->chunk->contents,                    \
 423                                      (h)->alignment_mask))
 424
 425 /* Note that the call to _obstack_newchunk is enclosed in (..., 0)
 426    so that we can avoid having void expressions
 427    in the arms of the conditional expression.
 428    Casting the third operand to void was tried before,
 429    but some compilers won't accept it.  */
 430
 431 # define obstack_make_room(h, length)                                         \
 432   ((h)->temp.tempint = (length),                                              \
 433    (((h)->next_free + (h)->temp.tempint > (h)->chunk_limit)                   \
 434    ? (_obstack_newchunk ((h), (h)->temp.tempint), 0) : 0))
 435
 436 # define obstack_grow(h, where, length)                                       \
 437   ((h)->temp.tempint = (length),                                              \
 438    (((h)->next_free + (h)->temp.tempint > (h)->chunk_limit)                   \
 439    ? (_obstack_newchunk ((h), (h)->temp.tempint), 0) : 0),                    \
 440    memcpy ((h)->next_free, where, (h)->temp.tempint),                         \
 441    (h)->next_free += (h)->temp.tempint)
 442
 443 # define obstack_grow0(h, where, length)                                      \
 444   ((h)->temp.tempint = (length),                                              \
 445    (((h)->next_free + (h)->temp.tempint + 1 > (h)->chunk_limit)               \
 446    ? (_obstack_newchunk ((h), (h)->temp.tempint + 1), 0) : 0),                \
 447    memcpy ((h)->next_free, where, (h)->temp.tempint),                         \
 448    (h)->next_free += (h)->temp.tempint,                                       \
 449    *((h)->next_free)++ = 0)
 450
 451 # define obstack_1grow(h, datum)                                              \
 452   ((((h)->next_free + 1 > (h)->chunk_limit)                                   \
 453     ? (_obstack_newchunk ((h), 1), 0) : 0),                                   \
 454    obstack_1grow_fast (h, datum))
 455
 456 # define obstack_ptr_grow(h, datum)                                           \
 457   ((((h)->next_free + sizeof (char *) > (h)->chunk_limit)                     \
 458     ? (_obstack_newchunk ((h), sizeof (char *)), 0) : 0),                     \
 459    obstack_ptr_grow_fast (h, datum))
 460
 461 # define obstack_int_grow(h, datum)                                           \
 462   ((((h)->next_free + sizeof (int) > (h)->chunk_limit)                        \
 463     ? (_obstack_newchunk ((h), sizeof (int)), 0) : 0),                        \
 464    obstack_int_grow_fast (h, datum))
 465
 466 # define obstack_ptr_grow_fast(h, aptr)                                       \
 467   (((const void **) ((h)->next_free += sizeof (void *)))[-1] = (aptr))
 468
 469 # define obstack_int_grow_fast(h, aint)                                       \
 470   (((int *) ((h)->next_free += sizeof (int)))[-1] = (aint))
 471
 472 # define obstack_blank(h, length)                                             \
 473   ((h)->temp.tempint = (length),                                              \
 474    (((h)->chunk_limit - (h)->next_free < (h)->temp.tempint)                   \
 475    ? (_obstack_newchunk ((h), (h)->temp.tempint), 0) : 0),                    \
 476    obstack_blank_fast (h, (h)->temp.tempint))
 477
 478 # define obstack_alloc(h, length)                                             \
 479   (obstack_blank ((h), (length)), obstack_finish ((h)))
 480
 481 # define obstack_copy(h, where, length)                                       \
 482   (obstack_grow ((h), (where), (length)), obstack_finish ((h)))
 483
 484 # define obstack_copy0(h, where, length)                                      \
 485   (obstack_grow0 ((h), (where), (length)), obstack_finish ((h)))
 486
 487 # define obstack_finish(h)                                                    \
 488   (((h)->next_free == (h)->object_base                                        \
 489     ? (((h)->maybe_empty_object = 1), 0)                                      \
 490     : 0),                                                                     \
 491    (h)->temp.tempptr = (h)->object_base,                                      \
 492    (h)->next_free                                                             \
 493      = __PTR_ALIGN ((h)->object_base, (h)->next_free,                         \
 494                     (h)->alignment_mask),                                     \
 495    (((h)->next_free - (char *) (h)->chunk                                     \
 496      > (h)->chunk_limit - (char *) (h)->chunk)                                \
 497    ? ((h)->next_free = (h)->chunk_limit) : 0),                                \
 498    (h)->object_base = (h)->next_free,                                         \
 499    (h)->temp.tempptr)
 500
 501 # define obstack_free(h, obj)                                                 \
 502   ((h)->temp.tempint = (char *) (obj) - (char *) (h)->chunk,                  \
 503    ((((h)->temp.tempint > 0                                                   \
 504       && (h)->temp.tempint < (h)->chunk_limit - (char *) (h)->chunk))         \
 505     ? (void) ((h)->next_free = (h)->object_base                               \
 506               = (h)->temp.tempint + (char *) (h)->chunk)                      \
 507     : (__obstack_free) (h, (h)->temp.tempint + (char *) (h)->chunk)))
 508
 509 #endif /* not __GNUC__ */
 510
 511 #ifdef __cplusplus
 512 }       /* C++ */
 513 #endif
 514
 515 #endif /* obstack.h */