From f1ce8a5cc28cecb7448ca786a6006618cd1c1ddf Mon Sep 17 00:00:00 2001
From: martynshaw99 <martynshaw99@47890b92-0858-11df-a26f-8b716316a5bc>
Date: Mon, 17 Feb 2014 00:00:59 +0000
Subject: [PATCH] Optimisation for speed, due to some code I found in an FFT
 routine.

---
 src/effects/Equalization.cpp | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/effects/Equalization.cpp b/src/effects/Equalization.cpp
index 428063d12..3c189fe27 100644
--- a/src/effects/Equalization.cpp
+++ b/src/effects/Equalization.cpp
@@ -831,11 +831,21 @@ void EqualizationPanel::OnPaint(wxPaintEvent &  WXUNUSED(event))
       freq = lin ? step*i : pow(10., loLog + i*step);   //Hz
       if( ( lin ? step : (pow(10., loLog + (i+1)*step)-freq) ) < delta)
       {   //not enough resolution in FFT
-         freq = M_PI*freq/mHiFreq;   //radians, normalized
+         // set up for calculating cos using recurrance - faster than calculating it directly each time
+         double theta = M_PI*freq/mHiFreq;   //radians, normalized
+         double wtemp = sin(0.5 * theta);
+         double wpr = -2.0 * wtemp * wtemp;
+         double wpi = -1.0 * sin(theta);
+         double wr = cos(theta*halfM);
+         double wi = sin(theta*halfM);
+
          yF = 0.;
          for(int j=0;j<halfM;j++)
          {
-            yF += 2. * mOutr[j] * cos(freq*(halfM-j));
+            yF += 2. * mOutr[j] * wr;  // This works for me, compared to the previous version.  Compare wr to cos(theta*(halfM-j)).  Works for me.  Keep everything as doubles though.
+            // do recurrance
+            wr = (wtemp = wr) * wpr - wi * wpi + wr;
+            wi = wi * wpr + wtemp * wpi + wi;
          }
          yF += mOutr[halfM];
          yF = fabs(yF);