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/* Safe automatic memory allocation.
Copyright (C) 2003-2006 Free Software Foundation, Inc.
Written by Bruno Haible <>, 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 3, 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
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, see <>. */
#ifndef _ALLOCSA_H
#define _ALLOCSA_H
#include <alloca.h>
#include <stddef.h>
#include <stdlib.h>
#ifdef __cplusplus
extern "C" {
/* 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.
/* 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)
# define safe_alloca(N) ((N), NULL)
/* 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. */
# define allocsa(N) \
((N) < 4032 - sa_increment \
? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \
: mallocsa (N))
# define allocsa(N) \
mallocsa (N)
extern void * mallocsa (size_t n);
/* Free a block of memory allocated through allocsa(). */
extern void freesa (void *p);
# define freesa free
/* 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. */
#ifdef __cplusplus
/* ------------------- 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)
#elif defined _AIX
/* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof
values. */
# define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
# define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
/* 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),
sa_alignment_longlong = sa_alignof (long long),
sa_alignment_longdouble = sa_alignof (long double),
sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1)
| (sa_alignment_longlong - 1)
| (sa_alignment_longdouble - 1)
) + 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 */