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diff --git a/lib/xalloc-oversized.h b/lib/xalloc-oversized.h
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+++ b/lib/xalloc-oversized.h
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+/* xalloc-oversized.h -- memory allocation size checking
+
+   Copyright (C) 1990-2000, 2003-2004, 2006-2018 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+#ifndef XALLOC_OVERSIZED_H_
+#define XALLOC_OVERSIZED_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+/* True if N * S would overflow in a size_t calculation,
+   or would generate a value larger than PTRDIFF_MAX.
+   This expands to a constant expression if N and S are both constants.
+   By gnulib convention, SIZE_MAX represents overflow in size
+   calculations, so the conservative size_t-based dividend to use here
+   is SIZE_MAX - 1.  */
+#define __xalloc_oversized(n, s) \
+  ((size_t) (PTRDIFF_MAX < SIZE_MAX ? PTRDIFF_MAX : SIZE_MAX - 1) / (s) < (n))
+
+#if PTRDIFF_MAX < SIZE_MAX
+typedef ptrdiff_t __xalloc_count_type;
+#else
+typedef size_t __xalloc_count_type;
+#endif
+
+/* Return 1 if an array of N objects, each of size S, cannot exist
+   reliably due to size or ptrdiff_t arithmetic overflow.  S must be
+   positive and N must be nonnegative.  This is a macro, not a
+   function, so that it works correctly even when SIZE_MAX < N.  */
+
+#if 7 <= __GNUC__
+# define xalloc_oversized(n, s) \
+   __builtin_mul_overflow_p (n, s, (__xalloc_count_type) 1)
+#elif 5 <= __GNUC__ && !defined __ICC && !__STRICT_ANSI__
+# define xalloc_oversized(n, s) \
+   (__builtin_constant_p (n) && __builtin_constant_p (s) \
+    ? __xalloc_oversized (n, s) \
+    : ({ __xalloc_count_type __xalloc_count; \
+         __builtin_mul_overflow (n, s, &__xalloc_count); }))
+
+/* Other compilers use integer division; this may be slower but is
+   more portable.  */
+#else
+# define xalloc_oversized(n, s) __xalloc_oversized (n, s)
+#endif
+
+#endif /* !XALLOC_OVERSIZED_H_ */