| 1 | /* Safe automatic memory allocation.
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| 2 | Copyright (C) 2003-2007, 2009-2012 Free Software Foundation, Inc.
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| 3 | Written by Bruno Haible <bruno@clisp.org>, 2003.
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| 4 |
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| 5 | This program is free software; you can redistribute it and/or modify
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| 6 | it under the terms of the GNU General Public License as published by
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| 7 | the Free Software Foundation; either version 3, or (at your option)
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| 8 | any later version.
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| 9 |
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| 10 | This program is distributed in the hope that it will be useful,
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| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 13 | GNU General Public License for more details.
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| 14 |
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| 15 | You should have received a copy of the GNU General Public License
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| 16 | along with this program; if not, see <http://www.gnu.org/licenses/>. */
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| 17 |
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| 18 | #ifndef _MALLOCA_H
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| 19 | #define _MALLOCA_H
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| 20 |
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| 21 | #include <alloca.h>
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| 22 | #include <stddef.h>
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| 23 | #include <stdlib.h>
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| 24 |
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| 25 |
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| 26 | #ifdef __cplusplus
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| 27 | extern "C" {
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| 28 | #endif
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| 29 |
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| 30 |
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| 31 | /* safe_alloca(N) is equivalent to alloca(N) when it is safe to call
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| 32 | alloca(N); otherwise it returns NULL. It either returns N bytes of
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| 33 | memory allocated on the stack, that lasts until the function returns,
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| 34 | or NULL.
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| 35 | Use of safe_alloca should be avoided:
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| 36 | - inside arguments of function calls - undefined behaviour,
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| 37 | - in inline functions - the allocation may actually last until the
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| 38 | calling function returns.
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| 39 | */
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| 40 | #if HAVE_ALLOCA
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| 41 | /* The OS usually guarantees only one guard page at the bottom of the stack,
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| 42 | and a page size can be as small as 4096 bytes. So we cannot safely
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| 43 | allocate anything larger than 4096 bytes. Also care for the possibility
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| 44 | of a few compiler-allocated temporary stack slots.
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| 45 | This must be a macro, not an inline function. */
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| 46 | # define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL)
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| 47 | #else
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| 48 | # define safe_alloca(N) ((void) (N), NULL)
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| 49 | #endif
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| 50 |
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| 51 | /* malloca(N) is a safe variant of alloca(N). It allocates N bytes of
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| 52 | memory allocated on the stack, that must be freed using freea() before
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| 53 | the function returns. Upon failure, it returns NULL. */
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| 54 | #if HAVE_ALLOCA
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| 55 | # define malloca(N) \
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| 56 | ((N) < 4032 - sa_increment \
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| 57 | ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \
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| 58 | : mmalloca (N))
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| 59 | #else
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| 60 | # define malloca(N) \
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| 61 | mmalloca (N)
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| 62 | #endif
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| 63 | extern void * mmalloca (size_t n);
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| 64 |
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| 65 | /* Free a block of memory allocated through malloca(). */
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| 66 | #if HAVE_ALLOCA
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| 67 | extern void freea (void *p);
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| 68 | #else
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| 69 | # define freea free
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| 70 | #endif
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| 71 |
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| 72 | /* nmalloca(N,S) is an overflow-safe variant of malloca (N * S).
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| 73 | It allocates an array of N objects, each with S bytes of memory,
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| 74 | on the stack. S must be positive and N must be nonnegative.
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| 75 | The array must be freed using freea() before the function returns. */
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| 76 | #if 1
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| 77 | /* Cf. the definition of xalloc_oversized. */
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| 78 | # define nmalloca(n, s) \
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| 79 | ((n) > (size_t) (sizeof (ptrdiff_t) <= sizeof (size_t) ? -1 : -2) / (s) \
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| 80 | ? NULL \
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| 81 | : malloca ((n) * (s)))
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| 82 | #else
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| 83 | extern void * nmalloca (size_t n, size_t s);
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| 84 | #endif
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| 85 |
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| 86 |
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| 87 | #ifdef __cplusplus
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| 88 | }
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| 89 | #endif
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| 90 |
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| 91 |
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| 92 | /* ------------------- Auxiliary, non-public definitions ------------------- */
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| 93 |
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| 94 | /* Determine the alignment of a type at compile time. */
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| 95 | #if defined __GNUC__
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| 96 | # define sa_alignof __alignof__
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| 97 | #elif defined __cplusplus
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| 98 | template <class type> struct sa_alignof_helper { char __slot1; type __slot2; };
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| 99 | # define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2)
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| 100 | #elif defined __hpux
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| 101 | /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof
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| 102 | values. */
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| 103 | # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
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| 104 | #elif defined _AIX
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| 105 | /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof
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| 106 | values. */
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| 107 | # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
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| 108 | #else
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| 109 | # define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
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| 110 | #endif
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| 111 |
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| 112 | enum
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| 113 | {
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| 114 | /* The desired alignment of memory allocations is the maximum alignment
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| 115 | among all elementary types. */
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| 116 | sa_alignment_long = sa_alignof (long),
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| 117 | sa_alignment_double = sa_alignof (double),
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| 118 | #if HAVE_LONG_LONG_INT
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| 119 | sa_alignment_longlong = sa_alignof (long long),
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| 120 | #endif
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| 121 | sa_alignment_longdouble = sa_alignof (long double),
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| 122 | sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1)
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| 123 | #if HAVE_LONG_LONG_INT
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| 124 | | (sa_alignment_longlong - 1)
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| 125 | #endif
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| 126 | | (sa_alignment_longdouble - 1)
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| 127 | ) + 1,
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| 128 | /* The increment that guarantees room for a magic word must be >= sizeof (int)
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| 129 | and a multiple of sa_alignment_max. */
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| 130 | sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max
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| 131 | };
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| 132 |
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| 133 | #endif /* _MALLOCA_H */
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