1 files changed, 12 insertions, 0 deletions
diff --git a/git-compat-util.h b/git-compat-util.h
index 81883e7..2af8d3e 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -28,6 +28,18 @@
 #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