From 95c46d8b7b03b1e0fce5169e78474cb2163ccde4 Mon Sep 17 00:00:00 2001 From: Loic Prylli Date: Wed, 10 Apr 2019 14:25:35 -0700 Subject: [PATCH] Fix wrap-aware isAfter function in Congestion.cxx Result of overflow on signed integer arithmetic is undefined in C/C++ standard. So in previous version clang was compiling the statement as (int)a > (int)b (i.e. assuming no overflow), which leads to incorrect result. Correct deterministic behavior means doing overflow arithmetic as unsigned, i.e. a != b && a - b <= UINT_MAX / 2 --- common/rfb/Congestion.cxx | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/common/rfb/Congestion.cxx b/common/rfb/Congestion.cxx index 4a784522..f3f9ceea 100644 --- a/common/rfb/Congestion.cxx +++ b/common/rfb/Congestion.cxx @@ -70,7 +70,7 @@ static const unsigned MAXIMUM_WINDOW = 4194304; // Compare position even when wrapped around static inline bool isAfter(unsigned a, unsigned b) { - return (int)a - (int)b > 0; + return a != b && a - b <= UINT_MAX / 2; } static LogWriter vlog("Congestion"); -- 2.39.5