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65 lines
2.6 KiB
C
65 lines
2.6 KiB
C
/* xalloc-oversized.h -- memory allocation size checking
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Copyright (C) 1990-2000, 2003-2004, 2006-2024 Free Software Foundation, Inc.
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This file is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as
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published by the Free Software Foundation; either version 2.1 of the
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License, or (at your option) any later version.
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This file 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 Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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#ifndef XALLOC_OVERSIZED_H_
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#define XALLOC_OVERSIZED_H_
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#include <stddef.h>
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#include <stdint.h>
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/* True if N * S does not fit into both ptrdiff_t and size_t.
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N and S should be nonnegative and free of side effects.
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This expands to a constant expression if N and S are both constants.
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By gnulib convention, SIZE_MAX represents overflow in size_t
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calculations, so the conservative size_t-based dividend to use here
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is SIZE_MAX - 1. */
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#define __xalloc_oversized(n, s) \
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((s) != 0 \
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&& (PTRDIFF_MAX < SIZE_MAX ? PTRDIFF_MAX : SIZE_MAX - 1) / (s) < (n))
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/* Return 1 if and only if an array of N objects, each of size S,
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cannot exist reliably because its total size in bytes would exceed
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MIN (PTRDIFF_MAX, SIZE_MAX - 1).
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N and S should be nonnegative and free of side effects.
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Warning: (xalloc_oversized (N, S) ? NULL : malloc (N * S)) can
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misbehave if N and S are both narrower than ptrdiff_t and size_t,
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and can be rewritten as (xalloc_oversized (N, S) ? NULL
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: malloc (N * (size_t) S)).
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This is a macro, not a function, so that it works even if an
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argument exceeds MAX (PTRDIFF_MAX, SIZE_MAX). */
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#if 7 <= __GNUC__ && !defined __clang__ && PTRDIFF_MAX < SIZE_MAX
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# define xalloc_oversized(n, s) \
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__builtin_mul_overflow_p (n, s, (ptrdiff_t) 1)
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#elif 5 <= __GNUC__ && !defined __ICC && PTRDIFF_MAX < SIZE_MAX
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# define xalloc_oversized(n, s) \
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(__builtin_constant_p (n) && __builtin_constant_p (s) \
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? __xalloc_oversized (n, s) \
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: __extension__ \
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({ ptrdiff_t __xalloc_count; \
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__builtin_mul_overflow (n, s, &__xalloc_count); }))
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/* Other compilers use integer division; this may be slower but is
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more portable. */
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#else
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# define xalloc_oversized(n, s) __xalloc_oversized (n, s)
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#endif
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#endif /* !XALLOC_OVERSIZED_H_ */
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