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+/* Safe automatic memory allocation.
+ Copyright (C) 2003-2004 Free Software Foundation, Inc.
+ Written by Bruno Haible <bruno@clisp.org>, 2003.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 2, or (at your option)
+ any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software Foundation,
+ Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
+
+#ifndef _ALLOCSA_H
+#define _ALLOCSA_H
+
+#include <alloca.h>
+#include <stddef.h>
+#include <stdlib.h>
+
+/* safe_alloca(N) is equivalent to alloca(N) when it is safe to call
+ alloca(N); otherwise it returns NULL. It either returns N bytes of
+ memory allocated on the stack, that lasts until the function returns,
+ or NULL.
+ Use of safe_alloca should be avoided:
+ - inside arguments of function calls - undefined behaviour,
+ - in inline functions - the allocation may actually last until the
+ calling function returns.
+*/
+#if HAVE_ALLOCA
+/* The OS usually guarantees only one guard page at the bottom of the stack,
+ and a page size can be as small as 4096 bytes. So we cannot safely
+ allocate anything larger than 4096 bytes. Also care for the possibility
+ of a few compiler-allocated temporary stack slots.
+ This must be a macro, not an inline function. */
+# define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL)
+#else
+# define safe_alloca(N) ((N), NULL)
+#endif
+
+/* allocsa(N) is a safe variant of alloca(N). It allocates N bytes of
+ memory allocated on the stack, that must be freed using freesa() before
+ the function returns. Upon failure, it returns NULL. */
+#if HAVE_ALLOCA
+# define allocsa(N) \
+ ((N) < 4032 - sa_increment \
+ ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \
+ : mallocsa (N))
+#else
+# define allocsa(N) \
+ mallocsa (N)
+#endif
+extern void * mallocsa (size_t n);
+
+/* Free a block of memory allocated through allocsa(). */
+#if HAVE_ALLOCA
+extern void freesa (void *p);
+#else
+# define freesa free
+#endif
+
+/* Maybe we should also define a variant
+ nallocsa (size_t n, size_t s) - behaves like allocsa (n * s)
+ If this would be useful in your application. please speak up. */
+
+
+/* ------------------- Auxiliary, non-public definitions ------------------- */
+
+/* Determine the alignment of a type at compile time. */
+#if defined __GNUC__
+# define sa_alignof __alignof__
+#elif defined __cplusplus
+ template <class type> struct sa_alignof_helper { char __slot1; type __slot2; };
+# define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2)
+#elif defined __hpux
+ /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof
+ values. */
+# define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
+#else
+# define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
+#endif
+
+enum
+{
+/* The desired alignment of memory allocations is the maximum alignment
+ among all elementary types. */
+ sa_alignment_long = sa_alignof (long),
+ sa_alignment_double = sa_alignof (double),
+#ifdef HAVE_LONG_LONG
+ sa_alignment_longlong = sa_alignof (long long),
+#endif
+#ifdef HAVE_LONG_DOUBLE
+ sa_alignment_longdouble = sa_alignof (long double),
+#endif
+ sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1)
+#ifdef HAVE_LONG_LONG
+ | (sa_alignment_longlong - 1)
+#endif
+#ifdef HAVE_LONG_DOUBLE
+ | (sa_alignment_longdouble - 1)
+#endif
+ ) + 1,
+/* The increment that guarantees room for a magic word must be >= sizeof (int)
+ and a multiple of sa_alignment_max. */
+ sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max
+};
+
+#endif /* _ALLOCSA_H */

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