1/* Safe automatic memory allocation.
2   Copyright (C) 2003-2005 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
27#ifdef __cplusplus
28extern "C" {
29#endif
30
31
32/* safe_alloca(N) is equivalent to alloca(N) when it is safe to call
33   alloca(N); otherwise it returns NULL.  It either returns N bytes of
34   memory allocated on the stack, that lasts until the function returns,
35   or NULL.
36   Use of safe_alloca should be avoided:
37     - inside arguments of function calls - undefined behaviour,
38     - in inline functions - the allocation may actually last until the
39       calling function returns.
40*/
41#if HAVE_ALLOCA
42/* The OS usually guarantees only one guard page at the bottom of the stack,
43   and a page size can be as small as 4096 bytes.  So we cannot safely
44   allocate anything larger than 4096 bytes.  Also care for the possibility
45   of a few compiler-allocated temporary stack slots.
46   This must be a macro, not an inline function.  */
47# define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL)
48#else
49# define safe_alloca(N) ((N), NULL)
50#endif
51
52/* allocsa(N) is a safe variant of alloca(N).  It allocates N bytes of
53   memory allocated on the stack, that must be freed using freesa() before
54   the function returns.  Upon failure, it returns NULL.  */
55#if HAVE_ALLOCA
56# define allocsa(N) \
57  ((N) < 4032 - sa_increment					    \
58   ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \
59   : mallocsa (N))
60#else
61# define allocsa(N) \
62  mallocsa (N)
63#endif
64extern void * mallocsa (size_t n);
65
66/* Free a block of memory allocated through allocsa().  */
67#if HAVE_ALLOCA
68extern void freesa (void *p);
69#else
70# define freesa free
71#endif
72
73/* Maybe we should also define a variant
74    nallocsa (size_t n, size_t s) - behaves like allocsa (n * s)
75   If this would be useful in your application. please speak up.  */
76
77
78#ifdef __cplusplus
79}
80#endif
81
82
83/* ------------------- Auxiliary, non-public definitions ------------------- */
84
85/* Determine the alignment of a type at compile time.  */
86#if defined __GNUC__
87# define sa_alignof __alignof__
88#elif defined __cplusplus
89  template <class type> struct sa_alignof_helper { char __slot1; type __slot2; };
90# define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2)
91#elif defined __hpux
92  /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof
93     values.  */
94# define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
95#elif defined _AIX
96  /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof
97     values.  */
98# define sa_alignof(type) 4
99#else
100# define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
101#endif
102
103enum
104{
105/* The desired alignment of memory allocations is the maximum alignment
106   among all elementary types.  */
107  sa_alignment_long = sa_alignof (long),
108  sa_alignment_double = sa_alignof (double),
109#ifdef HAVE_LONG_LONG
110  sa_alignment_longlong = sa_alignof (long long),
111#endif
112#ifdef HAVE_LONG_DOUBLE
113  sa_alignment_longdouble = sa_alignof (long double),
114#endif
115  sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1)
116#ifdef HAVE_LONG_LONG
117		      | (sa_alignment_longlong - 1)
118#endif
119#ifdef HAVE_LONG_DOUBLE
120		      | (sa_alignment_longdouble - 1)
121#endif
122		     ) + 1,
123/* The increment that guarantees room for a magic word must be >= sizeof (int)
124   and a multiple of sa_alignment_max.  */
125  sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max
126};
127
128#endif /* _ALLOCSA_H */
129