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114 lines
4.0 KiB
C++
114 lines
4.0 KiB
C++
/* Safe automatic memory allocation.
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Copyright (C) 2003-2004 Free Software Foundation, Inc.
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Written by Bruno Haible <bruno@clisp.org>, 2003.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software Foundation,
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Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
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#ifndef _ALLOCSA_H
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#define _ALLOCSA_H
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#include <alloca.h>
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#include <stddef.h>
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#include <stdlib.h>
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/* safe_alloca(N) is equivalent to alloca(N) when it is safe to call
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alloca(N); otherwise it returns NULL. It either returns N bytes of
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memory allocated on the stack, that lasts until the function returns,
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or NULL.
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Use of safe_alloca should be avoided:
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- inside arguments of function calls - undefined behaviour,
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- in inline functions - the allocation may actually last until the
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calling function returns.
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*/
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#if HAVE_ALLOCA
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/* The OS usually guarantees only one guard page at the bottom of the stack,
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and a page size can be as small as 4096 bytes. So we cannot safely
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allocate anything larger than 4096 bytes. Also care for the possibility
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of a few compiler-allocated temporary stack slots.
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This must be a macro, not an inline function. */
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# define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL)
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#else
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# define safe_alloca(N) ((N), NULL)
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#endif
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/* allocsa(N) is a safe variant of alloca(N). It allocates N bytes of
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memory allocated on the stack, that must be freed using freesa() before
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the function returns. Upon failure, it returns NULL. */
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#if HAVE_ALLOCA
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# define allocsa(N) \
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((N) < 4032 - sa_increment \
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? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \
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: mallocsa (N))
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#else
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# define allocsa(N) \
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mallocsa (N)
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#endif
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extern void * mallocsa (size_t n);
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/* Free a block of memory allocated through allocsa(). */
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#if HAVE_ALLOCA
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extern void freesa (void *p);
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#else
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# define freesa free
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#endif
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/* Maybe we should also define a variant
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nallocsa (size_t n, size_t s) - behaves like allocsa (n * s)
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If this would be useful in your application. please speak up. */
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/* ------------------- Auxiliary, non-public definitions ------------------- */
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/* Determine the alignment of a type at compile time. */
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#if defined __GNUC__
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# define sa_alignof __alignof__
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#elif defined __cplusplus
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template <class type> struct sa_alignof_helper { char __slot1; type __slot2; };
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# define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2)
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#elif defined __hpux
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/* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof
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values. */
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# define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
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#else
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# define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
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#endif
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enum
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{
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/* The desired alignment of memory allocations is the maximum alignment
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among all elementary types. */
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sa_alignment_long = sa_alignof (long),
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sa_alignment_double = sa_alignof (double),
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#ifdef HAVE_LONG_LONG
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sa_alignment_longlong = sa_alignof (long long),
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#endif
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#ifdef HAVE_LONG_DOUBLE
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sa_alignment_longdouble = sa_alignof (long double),
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#endif
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sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1)
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#ifdef HAVE_LONG_LONG
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| (sa_alignment_longlong - 1)
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#endif
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#ifdef HAVE_LONG_DOUBLE
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| (sa_alignment_longdouble - 1)
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#endif
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) + 1,
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/* The increment that guarantees room for a magic word must be >= sizeof (int)
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and a multiple of sa_alignment_max. */
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sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max
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};
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#endif /* _ALLOCSA_H */
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