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/* Safe automatic memory allocation.
Copyright (C) 2003 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)
#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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