QtMir

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

  1. unlikelyResetStartTime
  2. Merge into trunk
Proposed by Albert Astals Cid on 2016-01-07
Status: Merged
Approved by: Gerry Boland on 2016-01-07
Approved revision: 431
Merged at revision: 446
Proposed branch: lp:~aacid/qtmir/unlikelyResetStartTime
Merge into: lp:qtmir
Prerequisite: lp:~aacid/qtmir/timestampsInPast
Diff against target: 16 lines (+3/-3)
1 file modified
src/common/timestamp_impl.h (+3/-3)
To merge this branch: bzr merge lp:~aacid/qtmir/unlikelyResetStartTime
Reviewer Review Type Date Requested Status
Gerry Boland 2016-01-07 Approve on 2016-01-07
Albert Astals Cid Pending
Review via email: mp+281843@code.launchpad.net

This proposal supersedes a proposal from 2015-12-15.

Commit Message

Provide branch prediction information to the if in compressTimestamp

Description of the Change

 * 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

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Albert Astals Cid (aacid) wrote : Posted in a previous version of this proposal

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) : Posted in a previous version of this proposal
review: Approve
Gerry Boland (gerboland) :
review: Approve

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1=== modified file 'src/common/timestamp_impl.h'
2--- src/common/timestamp_impl.h 2016-01-07 11:43:03 +0000
3+++ src/common/timestamp_impl.h 2016-01-07 11:43:03 +0000
4@@ -15,9 +15,9 @@
5 {
6 std::chrono::nanoseconds startTime = getStartTime(timestamp);
7
8- if ((std::chrono::nanoseconds::max() > T::max() &&
9- timestamp - startTime > std::chrono::nanoseconds(T::max()))
10- || timestamp < startTime) {
11+ if (Q_UNLIKELY((std::chrono::nanoseconds::max() > T::max() &&
12+ timestamp - startTime > std::chrono::nanoseconds(T::max()))
13+ || timestamp < startTime)) {
14 // we've overflowed the boundaries of the millisecond type.
15 // or the timestamp has travelled to the past
16 resetStartTime(timestamp);

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