1/* Safe automatic memory allocation.
2   Copyright (C) 2003 Free Software Foundation, Inc.
3   Written by Bruno Haible <bruno@clisp.org>, 2003.
4
5   This program is free software; you can redistribute it and/or modify
6   it under the terms of the GNU General Public License as published by
7   the Free Software Foundation; either version 2, or (at your option)
8   any 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 Foundation,
17   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
18
19#ifndef _ALLOCSA_H
20#define _ALLOCSA_H
21
22#include <alloca.h>
23#include <stddef.h>
24#include <stdlib.h>
25
26/* safe_alloca(N) is equivalent to alloca(N) when it is safe to call
27   alloca(N); otherwise it returns NULL.  It either returns N bytes of
28   memory allocated on the stack, that lasts until the function returns,
29   or NULL.
30   Use of safe_alloca should be avoided:
31     - inside arguments of function calls - undefined behaviour,
32     - in inline functions - the allocation may actually last until the
33       calling function returns.
34*/
35#if HAVE_ALLOCA
36/* The OS usually guarantees only one guard page at the bottom of the stack,
37   and a page size can be as small as 4096 bytes.  So we cannot safely
38   allocate anything larger than 4096 bytes.  Also care for the possibility
39   of a few compiler-allocated temporary stack slots.
40   This must be a macro, not an inline function.  */
41# define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL)
42#else
43# define safe_alloca(N) ((N), NULL)
44#endif
45
46/* allocsa(N) is a safe variant of alloca(N).  It allocates N bytes of
47   memory allocated on the stack, that must be freed using freesa() before
48   the function returns.  Upon failure, it returns NULL.  */
49#if HAVE_ALLOCA
50# define allocsa(N) \
51  ((N) < 4032 - sa_increment					    \
52   ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \
53   : mallocsa (N))
54#else
55# define allocsa(N) \
56  mallocsa (N)
57#endif
58extern void * mallocsa (size_t n);
59
60/* Free a block of memory allocated through allocsa().  */
61#if HAVE_ALLOCA
62extern void freesa (void *p);
63#else
64# define freesa free
65#endif
66
67/* Maybe we should also define a variant
68    nallocsa (size_t n, size_t s) - behaves like allocsa (n * s)
69   If this would be useful in your application. please speak up.  */
70
71
72/* ------------------- Auxiliary, non-public definitions ------------------- */
73
74/* Determine the alignment of a type at compile time.  */
75#if defined __GNUC__
76# define sa_alignof __alignof__
77#elif defined __cplusplus
78  template <class type> struct sa_alignof_helper { char __slot1; type __slot2; };
79# define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2)
80#else
81# define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
82#endif
83
84enum
85{
86/* The desired alignment of memory allocations is the maximum alignment
87   among all elementary types.  */
88  sa_alignment_long = sa_alignof (long),
89  sa_alignment_double = sa_alignof (double),
90#ifdef HAVE_LONG_LONG
91  sa_alignment_longlong = sa_alignof (long long),
92#endif
93#ifdef HAVE_LONG_DOUBLE
94  sa_alignment_longdouble = sa_alignof (long double),
95#endif
96  sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1)
97#ifdef HAVE_LONG_LONG
98		      | (sa_alignment_longlong - 1)
99#endif
100#ifdef HAVE_LONG_DOUBLE
101		      | (sa_alignment_longdouble - 1)
102#endif
103		     ) + 1,
104/* The increment that guarantees room for a magic word must be >= sizeof (int)
105   and a multiple of sa_alignment_max.  */
106  sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max
107};
108
109#endif /* _ALLOCSA_H */
110