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optimize the CircularAverageMagnitudeDifference method #620

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optimize the CircularAverageMagnitudeDifference method #620

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7 changes: 6 additions & 1 deletion src/base/URecord.pas
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Original file line number Diff line number Diff line change
Expand Up @@ -489,17 +489,22 @@ function TCaptureBuffer.CircularAverageMagnitudeDifference(): TCorrelationArray;
ToneIndex: integer;
Correlation: TCorrelationArray;
SampleIndex: integer; // index of sample to analyze
const
// the value is fairly arbitrarily chosen, but this makes it analyze only 4096/SampleIndexStep samples
SampleIndexStep = 16;
begin
// accumulate the magnitude differences for samples in AnalysisBuffer
for ToneIndex := 0 to NumHalftones-1 do
begin
Correlation[ToneIndex] := 0;
for SampleIndex := 0 to (AnalysisBufferSize-1) do
SampleIndex := 0;
while SampleIndex < AnalysisBufferSize - 1 do
begin
// Suggestion for calculation efficiency improvement from deuteragenie:
// Replacing 'i mod buffersize' by 'i & (buffersize-1)' when i is positive and buffersize is a power of two should speed the modulo compuation by 5x-10x
//Correlation[ToneIndex] += Abs(AnalysisBuffer[(SampleIndex+Delays[ToneIndex]) mod AnalysisBufferSize] - AnalysisBuffer[SampleIndex]);
Correlation[ToneIndex] := Correlation[ToneIndex] + Abs(AnalysisBuffer[(SampleIndex+Delays[ToneIndex]) and (AnalysisBufferSize-1)] - AnalysisBuffer[SampleIndex]);
SampleIndex := SampleIndex + SampleIndexStep;
end;
Correlation[ToneIndex] := Correlation[ToneIndex] / AnalysisBufferSize;
end;
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