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+/* xalloc-oversized.h -- memory allocation size checking
+
+ Copyright (C) 1990-2000, 2003-2004, 2006-2017 Free Software Foundation, Inc.
+
+ This program is free software: you can redistribute it and/or
+ modify it under the terms of either:
+
+ * the GNU Lesser General Public License as published by the Free
+ Software Foundation; either version 3 of the License, or (at your
+ option) any later version.
+
+ or
+
+ * the GNU General Public License as published by the Free
+ Software Foundation; either version 2 of the License, or (at your
+ option) any later version.
+
+ or both in parallel, as here.
+ 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_ */