glib/galloca.h

   1 /* GLIB - Library of useful routines for C programming
   2  * Copyright (C) 1995-1997  Peter Mattis, Spencer Kimball and Josh MacDonald
   3  *
   4  * This library is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU Lesser General Public
   6  * License as published by the Free Software Foundation; either
   7  * version 2 of the License, or (at your option) any later version.
   8  *
   9  * This library is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * Lesser General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Lesser General Public
  15  * License along with this library; if not, write to the
  16  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17  * Boston, MA 02111-1307, USA.
  18  */
  19
  20 /*
  21  * Modified by the GLib Team and others 1997-2000.  See the AUTHORS
  22  * file for a list of people on the GLib Team.  See the ChangeLog
  23  * files for a list of changes.  These files are distributed with
  24  * GLib at ftp://ftp.gtk.org/pub/gtk/.
  25  */
  26
  27 #if !defined (__GLIB_H_INSIDE__) && !defined (GLIB_COMPILATION)
  28 #error "Only <glib.h> can be included directly."
  29 #endif
  30
  31 #ifndef __G_ALLOCA_H__
  32 #define __G_ALLOCA_H__
  33
  34 #include <glib/gtypes.h>
  35
  36 #ifdef  __GNUC__
  37 /* GCC does the right thing */
  38 # undef alloca
  39 # define alloca(size)   __builtin_alloca (size)
  40 #elif defined (GLIB_HAVE_ALLOCA_H)
  41 /* a native and working alloca.h is there */
  42 # include <alloca.h>
  43 #else /* !__GNUC__ && !GLIB_HAVE_ALLOCA_H */
  44 # if defined(_MSC_VER) || defined(__DMC__)
  45 #  include <malloc.h>
  46 #  define alloca _alloca
  47 # else /* !_MSC_VER && !__DMC__ */
  48 #  ifdef _AIX
  49 #   pragma alloca
  50 #  else /* !_AIX */
  51 #   ifndef alloca /* predefined by HP cc +Olibcalls */
  52 G_BEGIN_DECLS
  53 char *alloca ();
  54 G_END_DECLS
  55 #   endif /* !alloca */
  56 #  endif /* !_AIX */
  57 # endif /* !_MSC_VER && !__DMC__ */
  58 #endif /* !__GNUC__ && !GLIB_HAVE_ALLOCA_H */
  59
  60 /**
  61  * g_alloca:
  62  * @size: number of bytes to allocate.
  63  *
  64  * Allocates @size bytes on the stack; these bytes will be freed when the current
  65  * stack frame is cleaned up. This macro essentially just wraps the alloca()
  66  * function present on most UNIX variants.
  67  * Thus it provides the same advantages and pitfalls as alloca():
  68  * <variablelist>
  69  *   <varlistentry><term></term><listitem><para>
  70  *     + alloca() is very fast, as on most systems it's implemented by just adjusting
  71  *     the stack pointer register.
  72  *   </para></listitem></varlistentry>
  73  *   <varlistentry><term></term><listitem><para>
  74  *     + It doesn't cause any memory fragmentation, within its scope, separate alloca()
  75  *     blocks just build up and are released together at function end.
  76  *   </para></listitem></varlistentry>
  77  *   <varlistentry><term></term><listitem><para>
  78  *     - Allocation sizes have to fit into the current stack frame. For instance in a
  79  *       threaded environment on Linux, the per-thread stack size is limited to 2 Megabytes,
  80  *       so be sparse with alloca() uses.
  81  *   </para></listitem></varlistentry>
  82  *   <varlistentry><term></term><listitem><para>
  83  *     - Allocation failure due to insufficient stack space is not indicated with a %NULL
  84  *       return like e.g. with malloc(). Instead, most systems probably handle it the same
  85  *       way as out of stack space situations from infinite function recursion, i.e.
  86  *       with a segmentation fault.
  87  *   </para></listitem></varlistentry>
  88  *   <varlistentry><term></term><listitem><para>
  89  *     - Special care has to be taken when mixing alloca() with GNU C variable sized arrays.
  90  *       Stack space allocated with alloca() in the same scope as a variable sized array
  91  *       will be freed together with the variable sized array upon exit of that scope, and
  92  *       not upon exit of the enclosing function scope.
  93  *   </para></listitem></varlistentry>
  94  * </variablelist>
  95  *
  96  * Returns: space for @size bytes, allocated on the stack
  97  */
  98 #define g_alloca(size)           alloca (size)
  99 /**
 100  * g_newa:
 101  * @struct_type: Type of memory chunks to be allocated
 102  * @n_structs: Number of chunks to be allocated
 103  *
 104  * Wraps g_alloca() in a more typesafe manner.
 105  *
 106  * Returns: Pointer to stack space for @n_structs chunks of type @struct_type
 107  */
 108 #define g_newa(struct_type, n_structs)  ((struct_type*) g_alloca (sizeof (struct_type) * (gsize) (n_structs)))
 109
 110 #endif /* __G_ALLOCA_H__ */