From 61a63a673ca3759d5c7c168cbad0e8cc9cacabb6 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Mon, 26 Nov 2018 22:34:04 -0500
Subject: [PATCH] Adds a negative operator.

---
 SignalProcessing/FIRFilter.cpp | 13 +++++++++++++
 SignalProcessing/FIRFilter.hpp |  5 +++++
 2 files changed, 18 insertions(+)

diff --git a/SignalProcessing/FIRFilter.cpp b/SignalProcessing/FIRFilter.cpp
index e7d593dd9..ef92db1f7 100644
--- a/SignalProcessing/FIRFilter.cpp
+++ b/SignalProcessing/FIRFilter.cpp
@@ -114,6 +114,9 @@ FIRFilter::FIRFilter(std::size_t number_of_taps, float input_sample_rate, float
 	std::size_t Np = (number_of_taps - 1) / 2;
 	float two_over_sample_rate = 2.0f / input_sample_rate;
 
+	// Clamp the high cutoff frequency.
+	high_frequency = std::min(high_frequency, input_sample_rate * 0.5f);
+
 	std::vector<float> A(Np+1);
 	A[0] = 2.0f * (high_frequency - low_frequency) / input_sample_rate;
 	for(unsigned int i = 1; i <= Np; ++i) {
@@ -146,6 +149,16 @@ FIRFilter FIRFilter::operator+(const FIRFilter &rhs) const {
 	return FIRFilter(sum);
 }
 
+FIRFilter FIRFilter::operator-() const {
+	std::vector<float> negative_coefficients;
+
+	for(const auto coefficient: get_coefficients()) {
+		negative_coefficients.push_back(1.0f - coefficient);
+	}
+
+	return FIRFilter(negative_coefficients);
+}
+
 FIRFilter FIRFilter::operator*(const FIRFilter &rhs) const {
 	std::vector<float> coefficients = get_coefficients();
 	std::vector<float> rhs_coefficients = rhs.get_coefficients();
diff --git a/SignalProcessing/FIRFilter.hpp b/SignalProcessing/FIRFilter.hpp
index c6c7e7e56..8ee2d09bd 100644
--- a/SignalProcessing/FIRFilter.hpp
+++ b/SignalProcessing/FIRFilter.hpp
@@ -83,6 +83,11 @@ class FIRFilter {
 		*/
 		FIRFilter operator*(const FIRFilter &) const;
 
+		/*!
+			@returns A filter that would have the opposite effect of this filter.
+		*/
+		FIRFilter operator-() const;
+
 	private:
 		std::vector<short> filter_coefficients_;