include/objalloc.h

   1 /* objalloc.h -- routines to allocate memory for objects
   2    Copyright 1997 Free Software Foundation, Inc.
   3    Written by Ian Lance Taylor, Cygnus Solutions.
   4
   5 This program is free software; you can redistribute it and/or modify it
   6 under the terms of the GNU General Public License as published by the
   7 Free Software Foundation; either version 2, or (at your option) any
   8 later version.
   9
  10 This program 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
  13 GNU General Public License for more details.
  14
  15 You should have received a copy of the GNU General Public License
  16 along with this program; if not, write to the Free Software
  17 Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
  18
  19 #ifndef OBJALLOC_H
  20 #define OBJALLOC_H
  21
  22 #include "ansidecl.h"
  23
  24 /* These routines allocate space for an object.  The assumption is
  25    that the object will want to allocate space as it goes along, but
  26    will never want to free any particular block.  There is a function
  27    to free a block, which also frees all more recently allocated
  28    blocks.  There is also a function to free all the allocated space.
  29
  30    This is essentially a specialization of obstacks.  The main
  31    difference is that a block may not be allocated a bit at a time.
  32    Another difference is that these routines are always built on top
  33    of malloc, and always pass an malloc failure back to the caller,
  34    unlike more recent versions of obstacks.  */
  35
  36 /* This is what an objalloc structure looks like.  Callers should not
  37    refer to these fields, nor should they allocate these structure
  38    themselves.  Instead, they should only create them via
  39    objalloc_init, and only access them via the functions and macros
  40    listed below.  The structure is only defined here so that we can
  41    access it via macros.  */
  42
  43 struct objalloc
  44 {
  45   char *current_ptr;
  46   unsigned int current_space;
  47   PTR chunks;
  48 };
  49
  50 /* Work out the required alignment.  */
  51
  52 struct objalloc_align { char x; double d; };
  53
  54 #if defined (__STDC__) && __STDC__
  55 #ifndef offsetof
  56 #include <stddef.h>
  57 #endif
  58 #define OBJALLOC_ALIGN \
  59   ((ptrdiff_t) ((char *) &((struct objalloc_align *) 0)->d - (char *) 0))
  60 #else
  61 #define OBJALLOC_ALIGN \
  62   ((long) ((char *) &((struct objalloc_align *) 0)->d - (char *) 0))
  63 #endif
  64
  65 /* Create an objalloc structure.  Returns NULL if malloc fails.  */
  66
  67 extern struct objalloc *objalloc_create PARAMS ((void));
  68
  69 /* Allocate space from an objalloc structure.  Returns NULL if malloc
  70    fails.  */
  71
  72 extern PTR _objalloc_alloc PARAMS ((struct objalloc *, unsigned long));
  73
  74 /* The macro version of objalloc_alloc.  We only define this if using
  75    gcc, because otherwise we would have to evaluate the arguments
  76    multiple times, or use a temporary field as obstack.h does.  */
  77
  78 #if defined (__GNUC__) && defined (__STDC__) && __STDC__
  79
  80 /* NextStep 2.0 cc is really gcc 1.93 but it defines __GNUC__ = 2 and
  81    does not implement __extension__.  But that compiler doesn't define
  82    __GNUC_MINOR__.  */
  83 #if __GNUC__ < 2 || (__NeXT__ && !__GNUC_MINOR__)
  84 #define __extension__
  85 #endif
  86
  87 #define objalloc_alloc(o, l)                                            \
  88   __extension__                                                         \
  89   ({ struct objalloc *__o = (o);                                        \
  90      unsigned long __len = (l);                                         \
  91      if (__len == 0)                                                    \
  92        __len = 1;                                                       \
  93      __len = (__len + OBJALLOC_ALIGN - 1) &~ (OBJALLOC_ALIGN - 1);      \
  94      (__len <= __o->current_space                                       \
  95       ? (__o->current_ptr += __len,                                     \
  96          __o->current_space -= __len,                                   \
  97          (PTR) (__o->current_ptr - __len))                              \
  98       : _objalloc_alloc (__o, __len)); })
  99
 100 #else /* ! __GNUC__ */
 101
 102 #define objalloc_alloc(o, l) _objalloc_alloc ((o), (l))
 103
 104 #endif /* ! __GNUC__ */
 105
 106 /* Free an entire objalloc structure.  */
 107
 108 extern void objalloc_free PARAMS ((struct objalloc *));
 109
 110 /* Free a block allocated by objalloc_alloc.  This also frees all more
 111    recently allocated blocks.  */
 112
 113 extern void objalloc_free_block PARAMS ((struct objalloc *, PTR));
 114
 115 #endif /* OBJALLOC_H */