From 45e2e7ef67825d0428963114ffc61bc95d58743a Mon Sep 17 00:00:00 2001
From: Mike Walters <mike@flomp.net>
Date: Sat, 4 Jun 2016 14:46:28 +0100
Subject: [PATCH] spectrogram: Pull some constants out of the loop

---
 spectrogramplot.cpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/spectrogramplot.cpp b/spectrogramplot.cpp
index fb947f9..291c3fc 100644
--- a/spectrogramplot.cpp
+++ b/spectrogramplot.cpp
@@ -142,13 +142,15 @@ void SpectrogramPlot::getLine(float *dest, off_t sample)
         }
 
         fft->process(buffer.get(), buffer.get());
+        const float invFFTSize = 1.0f / fftSize;
+        const float dbMult = 10.0f / log2f(10.0f);
         for (int i = 0; i < fftSize; i++) {
             // Start from the middle of the FFTW array and wrap
             // to rearrange the data
             int k = (i + fftSize / 2) & (fftSize - 1);
-            auto s = buffer[k] / (float)fftSize;
+            auto s = buffer[k] * invFFTSize;
             float mag = sqrt(s.real() * s.real() + s.imag() * s.imag());
-            float magdb = 10 * log2f(mag) / log2f(10);
+            float magdb = log2f(mag) * dbMult;
             *dest = magdb;
             dest++;
         }