#define ARRAY_SIZE(x) (sizeof(x)/sizeof(x[0]))
#define bitsizeof(x) (CHAR_BIT * sizeof(x))
+#define maximum_signed_value_of_type(a) \
+ (INTMAX_MAX >> (bitsizeof(intmax_t) - bitsizeof(a)))
+
+/*
+ * Signed integer overflow is undefined in C, so here's a helper macro
+ * to detect if the sum of two integers will overflow.
+ *
+ * Requires: a >= 0, typeof(a) equals typeof(b)
+ */
+#define signed_add_overflows(a, b) \
+ ((b) > maximum_signed_value_of_type(a) - (a))
+
#ifdef __GNUC__
#define TYPEOF(x) (__typeof__(x))
#else