Merge lp:~aacid/qtmir/unlikelyResetStartTime into lp:qtmir

[Albert Astals Cid]

Provide branch prediction information to the if in compressTimestamp

 * Are there any related MPs required for this MP to build/function as expected?
Prerequisite

 * Did you perform an exploratory manual test run of your code change and any related functionality?
Yes

 * If you changed the packaging (debian), did you subscribe the ubuntu-unity team to this MP?
N/A

[Albert Astals Cid (aacid)]

This seems a pretty hot path and 99.999% of the times the if evaluates to false so i thought it might make sense telling the compiler to optimize for that.

[Gerry Boland (gerboland)]

review: Approve

[Gerry Boland (gerboland)]

review: Approve

=== modified file 'src/common/timestamp_impl.h'
--- src/common/timestamp_impl.h	2016-01-07 11:43:03 +0000
+++ src/common/timestamp_impl.h	2016-01-07 11:43:03 +0000
@@ -15,9 +15,9 @@
 {
     std::chrono::nanoseconds startTime = getStartTime(timestamp);
 
-    if ((std::chrono::nanoseconds::max() > T::max() &&
-         timestamp - startTime > std::chrono::nanoseconds(T::max()))
-        || timestamp < startTime) {
+    if (Q_UNLIKELY((std::chrono::nanoseconds::max() > T::max() &&
+                    timestamp - startTime > std::chrono::nanoseconds(T::max()))
+                   || timestamp < startTime)) {
         // we've overflowed the boundaries of the millisecond type.
         // or the timestamp has travelled to the past
         resetStartTime(timestamp);