Small cleanup of IIR filter code.

TNC/IirFilter.hpp

@@ -1,4 +1,4 @@
-// Copyright 2015-2020 Rob Riggs <rob@mobilinkd.com>
+// Copyright 2015-2021 Rob Riggs <rob@mobilinkd.com>
 // All rights reserved.
 
 #pragma once
@@ -15,31 +15,32 @@ struct IirFilter {
 	const std::array<float, N>& numerator_;
 	const std::array<float, N>& denominator_;
 	std::array<float, N> history_;
-	size_t size_;
 
     IirFilter(const std::array<float, N>& b,
         const std::array<float, N>& a)
     : numerator_(b), denominator_(a)
-    , history_(), size_(N)
+    , history_()
     {
         history_.fill(0.0f);
     }
 
     ~IirFilter() {}
 
+    static constexpr size_t size() { return N; }
+
 	float operator()(float input)
 	{
 
-		for(size_t i = size_ - 1; i != 0; i--) history_[i] = history_[i - 1];
+		for (size_t i = N - 1; i != 0; i--) history_[i] = history_[i - 1];
 		
 		history_[0] = input;
 
-		for (size_t i = 1; i != size_; i++) {
+		for (size_t i = 1; i != N; i++) {
 			history_[0] -= denominator_[i] * history_[i];
 		}
 		
 		float result = 0;
-		for (size_t i = 0; i != size_; i++) {
+		for (size_t i = 0; i != N; i++) {
 			result += numerator_[i] * history_[i];
 		}
 		
@@ -48,5 +49,3 @@ struct IirFilter {
 };
 
 }} // mobilinkd::tnc
-
-