From a0299cc63aecdd668ee35785661f5cb42e3bc831 Mon Sep 17 00:00:00 2001
From: Bartosz Taudul <wolf.pld@gmail.com>
Date: Thu, 14 Mar 2019 01:23:37 +0100
Subject: [PATCH] Optimize calculation of standard deviation.

---
 server/TracyView.cpp   | 10 +++-------
 server/TracyWorker.cpp |  2 ++
 server/TracyWorker.hpp |  1 +
 3 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/server/TracyView.cpp b/server/TracyView.cpp
index ca2b8ec2..60ac721a 100644
--- a/server/TracyView.cpp
+++ b/server/TracyView.cpp
@@ -6029,14 +6029,10 @@ void View::DrawFindZone()
                         TextFocused( "Median time:", TimeToString( m_findZone.median ) );
                         if( m_findZone.sorted.size() > 1 )
                         {
+                            const auto sz = m_findZone.sorted.size();
                             const auto avg = m_findZone.average;
-                            double ss = 0;
-                            for( auto& v : m_findZone.sorted )
-                            {
-                                const auto d = double( v ) - avg;
-                                ss += d*d;
-                            }
-                            const auto sd = sqrt( ss / ( m_findZone.sorted.size() - 1 ) );
+                            const auto ss = zoneData.sumSq - 2. * zoneData.total * avg + avg * avg * sz;
+                            const auto sd = sqrt( ss / ( sz - 1 ) );
 
                             ImGui::SameLine();
                             ImGui::Spacing();
diff --git a/server/TracyWorker.cpp b/server/TracyWorker.cpp
index dddc7b7a..8f89d17d 100644
--- a/server/TracyWorker.cpp
+++ b/server/TracyWorker.cpp
@@ -2590,6 +2590,7 @@ void Worker::ProcessZoneEnd( const QueueZoneEnd& ev )
         slz.min = std::min( slz.min, timeSpan );
         slz.max = std::max( slz.max, timeSpan );
         slz.total += timeSpan;
+        slz.sumSq += double( timeSpan ) * timeSpan;
         if( zone->child >= 0 )
         {
             for( auto& v : GetZoneChildren( zone->child ) )
@@ -3587,6 +3588,7 @@ void Worker::ReadTimelineUpdateStatistics( ZoneEvent* zone, uint16_t thread )
             slz.min = std::min( slz.min, timeSpan );
             slz.max = std::max( slz.max, timeSpan );
             slz.total += timeSpan;
+            slz.sumSq += double( timeSpan ) * timeSpan;
             if( zone->child >= 0 )
             {
                 for( auto& v : GetZoneChildren( zone->child ) )
diff --git a/server/TracyWorker.hpp b/server/TracyWorker.hpp
index 9c2c1123..4847d0b7 100644
--- a/server/TracyWorker.hpp
+++ b/server/TracyWorker.hpp
@@ -86,6 +86,7 @@ private:
         int64_t min = std::numeric_limits<int64_t>::max();
         int64_t max = std::numeric_limits<int64_t>::min();
         int64_t total = 0;
+        double sumSq = 0;
         int64_t selfMin = std::numeric_limits<int64_t>::max();
         int64_t selfMax = std::numeric_limits<int64_t>::min();
         int64_t selfTotal = 0;