From 2298b6786935621e19c2bbbce6deb1d39e02d1a1 Mon Sep 17 00:00:00 2001
From: Chris Cannam <cannam@all-day-breakfast.com>
Date: Thu, 9 Jun 2022 16:39:30 +0100
Subject: [PATCH] Avoid recalculating window scale factor every time

---
 src/finer/R3StretcherImpl.cpp | 16 ++--------------
 src/finer/R3StretcherImpl.h   | 12 +++++++++++-
 2 files changed, 13 insertions(+), 15 deletions(-)

diff --git a/src/finer/R3StretcherImpl.cpp b/src/finer/R3StretcherImpl.cpp
index 95f088c..327ff1d 100644
--- a/src/finer/R3StretcherImpl.cpp
+++ b/src/finer/R3StretcherImpl.cpp
@@ -532,8 +532,6 @@ R3StretcherImpl::analyseChannel(int c, int inhop, int prevInhop, int prevOuthop)
     // where the inhop has changed as above, in which case we need to
     // do both readahead and current)
 
-    v_fftshift(readahead.timeDomain.data(), classify);
-
     if (haveValidReadahead) {
         v_copy(classifyScale->mag.data(),
                readahead.mag.data(),
@@ -543,6 +541,7 @@ R3StretcherImpl::analyseChannel(int c, int inhop, int prevInhop, int prevOuthop)
                classifyScale->bufSize);
     }
 
+    v_fftshift(readahead.timeDomain.data(), classify);
     m_scaleData.at(classify)->fft.forward(readahead.timeDomain.data(),
                                           classifyScale->real.data(),
                                           classifyScale->imag.data());
@@ -776,18 +775,7 @@ R3StretcherImpl::synthesiseChannel(int c, int outhop)
         auto &scale = cd->scales.at(fftSize);
         auto &scaleData = m_scaleData.at(fftSize);
 
-        //!!! messy and slow, but leave it until we've
-        //!!! discovered whether we need a window accumulator
-        //!!! (we probably do)
-        int analysisWindowSize = scaleData->analysisWindow.getSize();
-        int synthesisWindowSize = scaleData->synthesisWindow.getSize();
-        int offset = (analysisWindowSize - synthesisWindowSize) / 2;
-        double winscale = 0.0;
-        for (int i = 0; i < synthesisWindowSize; ++i) {
-            winscale += scaleData->analysisWindow.getValue(i + offset) *
-                scaleData->synthesisWindow.getValue(i);
-        }
-        winscale = double(outhop) / winscale;
+        double winscale = double(outhop) / scaleData->windowScaleFactor;
 
         // The frequency filter is applied naively in the frequency
         // domain. Aliasing is reduced by the shorter resynthesis
diff --git a/src/finer/R3StretcherImpl.h b/src/finer/R3StretcherImpl.h
index ab6db5f..7d5c8ee 100644
--- a/src/finer/R3StretcherImpl.h
+++ b/src/finer/R3StretcherImpl.h
@@ -233,6 +233,7 @@ protected:
         FFT fft;
         Window<double> analysisWindow;
         Window<double> synthesisWindow;
+        double windowScaleFactor;
         GuidedPhaseAdvance guided;
         ScaleData(GuidedPhaseAdvance::Parameters guidedParameters) :
             fftSize(guidedParameters.fftSize),
@@ -241,7 +242,16 @@ protected:
                            analysisWindowLength(fftSize)),
             synthesisWindow(synthesisWindowShape(fftSize),
                             synthesisWindowLength(fftSize)),
-            guided(guidedParameters) { }
+            guided(guidedParameters),
+            windowScaleFactor(0.0)
+        {
+            int asz = analysisWindow.getSize(), ssz = synthesisWindow.getSize();
+            int off = (asz - ssz) / 2;
+            for (int i = 0; i < ssz; ++i) {
+                windowScaleFactor += analysisWindow.getValue(i + off) *
+                    synthesisWindow.getValue(i);
+            }
+        }
 
         WindowType analysisWindowShape(int fftSize);
         int analysisWindowLength(int fftSize);