From 6578aaea02de43c38c7648e3924ee4015f54b88a Mon Sep 17 00:00:00 2001
From: Gregor Jasny <gjasny@googlemail.com>
Date: Sun, 9 Apr 2017 23:59:23 -0700
Subject: [PATCH] Avoid undefined behaviour at circular shift

Clang UBSAN complains about 64 bit wide shifts.
---
 websocketpp/frame.hpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/websocketpp/frame.hpp b/websocketpp/frame.hpp
index 8a173375a..18a990b36 100644
--- a/websocketpp/frame.hpp
+++ b/websocketpp/frame.hpp
@@ -610,6 +610,9 @@ inline size_t prepare_masking_key(const masking_key_type& key) {
  * to zero and less than sizeof(size_t).
  */
 inline size_t circshift_prepared_key(size_t prepared_key, size_t offset) {
+    if (offset == 0) {
+        return prepared_key;
+    }
     if (lib::net::is_little_endian()) {
         size_t temp = prepared_key << (sizeof(size_t)-offset)*8;
         return (prepared_key >> offset*8) | temp;