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1/* Safe automatic memory allocation.
2 Copyright (C) 2003-2007, 2009-2010 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 3, 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 _MALLOCA_H
20#define _MALLOCA_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) ((void) (N), NULL)
50#endif
51
52/* malloca(N) is a safe variant of alloca(N). It allocates N bytes of
53 memory allocated on the stack, that must be freed using freea() before
54 the function returns. Upon failure, it returns NULL. */
55#if HAVE_ALLOCA
56# define malloca(N) \
57 ((N) < 4032 - sa_increment \
58 ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \
59 : mmalloca (N))
60#else
61# define malloca(N) \
62 mmalloca (N)
63#endif
64extern void * mmalloca (size_t n);
65
66/* Free a block of memory allocated through malloca(). */
67#if HAVE_ALLOCA
68extern void freea (void *p);
69#else
70# define freea free
71#endif
72
73/* nmalloca(N,S) is an overflow-safe variant of malloca (N * S).
74 It allocates an array of N objects, each with S bytes of memory,
75 on the stack. S must be positive and N must be nonnegative.
76 The array must be freed using freea() before the function returns. */
77#if 1
78/* Cf. the definition of xalloc_oversized. */
79# define nmalloca(n, s) \
80 ((n) > (size_t) (sizeof (ptrdiff_t) <= sizeof (size_t) ? -1 : -2) / (s) \
81 ? NULL \
82 : malloca ((n) * (s)))
83#else
84extern void * nmalloca (size_t n, size_t s);
85#endif
86
87
88#ifdef __cplusplus
89}
90#endif
91
92
93/* ------------------- Auxiliary, non-public definitions ------------------- */
94
95/* Determine the alignment of a type at compile time. */
96#if defined __GNUC__
97# define sa_alignof __alignof__
98#elif defined __cplusplus
99 template <class type> struct sa_alignof_helper { char __slot1; type __slot2; };
100# define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2)
101#elif defined __hpux
102 /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof
103 values. */
104# define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
105#elif defined _AIX
106 /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof
107 values. */
108# define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
109#else
110# define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
111#endif
112
113enum
114{
115/* The desired alignment of memory allocations is the maximum alignment
116 among all elementary types. */
117 sa_alignment_long = sa_alignof (long),
118 sa_alignment_double = sa_alignof (double),
119#if HAVE_LONG_LONG_INT
120 sa_alignment_longlong = sa_alignof (long long),
121#endif
122 sa_alignment_longdouble = sa_alignof (long double),
123 sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1)
124#if HAVE_LONG_LONG_INT
125 | (sa_alignment_longlong - 1)
126#endif
127 | (sa_alignment_longdouble - 1)
128 ) + 1,
129/* The increment that guarantees room for a magic word must be >= sizeof (int)
130 and a multiple of sa_alignment_max. */
131 sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max
132};
133
134#endif /* _MALLOCA_H */