#include <stddef.h>
+/* Default for (non-Clang) compilers that lack __has_builtin. */
#ifndef __has_builtin
# define __has_builtin(x) 0
#endif
-/* Return 1 if an array of N objects, each of size S, cannot exist due
- to size 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.
-
+/* True if N * S would overflow in a size calculation.
+ 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 dividend to use here is
SIZE_MAX - 1, since SIZE_MAX might represent an overflowed value.
sizeof (ptrdiff_t) <= sizeof (size_t), so do not bother to test for
exactly-SIZE_MAX allocations on such hosts; this avoids a test and
branch when S is known to be 1. */
-#if 5 <= __GNUC__ || __has_builtin (__builtin_mul_overflow)
+#define __xalloc_oversized(n, s) \
+ ((size_t) (sizeof (ptrdiff_t) <= sizeof (size_t) ? -1 : -2) / (s) < (n))
+
+
+/* Return 1 if an array of N objects, each of size S, cannot exist due
+ to size 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. */
+
+/* GCC 7 __builtin_mul_overflow should easily compute this. See:
+ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68120 */
+#if 7 <= __GNUC__
+# define xalloc_oversized(n, s) __builtin_mul_overflow (n, s, (size_t *) NULL)
+
+/* GCC 5 and Clang __builtin_mul_overflow needs a temporary, and
+ should be used only for non-constant operands, so that
+ xalloc_oversized is a constant expression if both arguments are.
+ Do not use this if pedantic, since pedantic GCC issues a diagnostic
+ for ({ ... }). */
+#elif ((5 <= __GNUC__ \
+ || (__has_builtin (__builtin_mul_overflow) \
+ && __has_builtin (__builtin_constant_p))) \
+ && !__STRICT_ANSI__)
# define xalloc_oversized(n, s) \
- ({ size_t __xalloc_size; __builtin_mul_overflow (n, s, &__xalloc_size); })
+ (__builtin_constant_p (n) && __builtin_constant_p (s) \
+ ? __xalloc_oversized (n, s) \
+ : ({ size_t __xalloc_size; __builtin_mul_overflow (n, s, &__xalloc_size); }))
+
+/* Other compilers use integer division; this may be slower but is
+ more portable. */
#else
-# define xalloc_oversized(n, s) \
- ((size_t) (sizeof (ptrdiff_t) <= sizeof (size_t) ? -1 : -2) / (s) < (n))
+# define xalloc_oversized(n, s) __xalloc_oversized (n, s)
#endif
#endif /* !XALLOC_OVERSIZED_H_ */