1 files changed, 28 insertions, 0 deletions
diff --git a/src/lib/intmath/addsub.c b/src/lib/intmath/addsub.c
new file mode 100644
index 0000000000..12146f4e72
--- /dev/null
+++ b/src/lib/intmath/addsub.c
@@ -0,0 +1,28 @@
+/* Copyright (c) 2003-2004, Roger Dingledine
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2019, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file addsub.c
+ *
+ * \brief Helpers for addition and subtraction.
+ *
+ * Currently limited to non-wrapping (saturating) addition.
+ **/
+
+#include "lib/intmath/addsub.h"
+#include "lib/cc/compat_compiler.h"
+
+/* Helper: safely add two uint32_t's, capping at UINT32_MAX rather
+ * than overflow */
+uint32_t
+tor_add_u32_nowrap(uint32_t a, uint32_t b)
+{
+  /* a+b > UINT32_MAX check, without overflow */
+  if (PREDICT_UNLIKELY(a > UINT32_MAX - b)) {
+    return UINT32_MAX;
+  } else {
+    return a+b;
+  }
+}