From 26293db40f8ac62f3971e0e9dbbc0bf3439e61c0 Mon Sep 17 00:00:00 2001
From: Vasile Vilvoiu <vasi.vilvoiu@gmail.com>
Date: Tue, 29 Dec 2020 19:33:03 +0200
Subject: Initial commit

---
 src/window-function.cpp | 88 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 src/window-function.cpp

(limited to 'src/window-function.cpp')

diff --git a/src/window-function.cpp b/src/window-function.cpp
new file mode 100644
index 0000000..8f381ec
--- /dev/null
+++ b/src/window-function.cpp
@@ -0,0 +1,88 @@
+/*
+ * Copyright (c) 2020-2021 Vasile Vilvoiu <vasi.vilvoiu@gmail.com>
+ *
+ * specgram is free software; you can redistribute it and/or modify
+ * it under the terms of the MIT license. See LICENSE for details.
+ */
+#include "window-function.hpp"
+
+#include <cassert>
+
+WindowFunction::WindowFunction(std::size_t window_size) : window_size_(window_size)
+{
+    cached_factors_.resize(window_size);
+}
+
+std::unique_ptr<WindowFunction>
+WindowFunction::FromType(WindowFunctionType type, std::size_t window_size)
+{
+    switch (type) {
+        case WindowFunctionType::kNone:
+            return nullptr; /* no window needed */
+
+        case WindowFunctionType::kHann:
+            return std::make_unique<HannWindowFunction>(window_size);
+
+        case WindowFunctionType::kHamming:
+            return std::make_unique<HammingWindowFunction>(window_size);
+
+        case WindowFunctionType::kBlackman:
+            return std::make_unique<BlackmanWindowFunction>(window_size);
+
+        case WindowFunctionType::kNuttall:
+            return std::make_unique<NuttallWindowFunction>(window_size);
+
+        default:
+            throw std::runtime_error("unknown window function");
+    }
+}
+
+ComplexWindow
+WindowFunction::Apply(const ComplexWindow& window) const
+{
+    /* only matching windows */
+    if (window.size() != this->window_size_) {
+        throw std::runtime_error("incorrect window size for window function application");
+    }
+    assert(this->cached_factors_.size() == this->window_size_);
+
+    ComplexWindow output;
+    output.resize(this->window_size_);
+    for (std::size_t i = 0; i < this->window_size_; i++) {
+        output[i] = window[i] * this->cached_factors_[i];
+    }
+    return output;
+}
+
+GeneralizedCosineWindowFunction::GeneralizedCosineWindowFunction(std::size_t window_size,
+                                                                 const std::vector<double>& a)
+    : WindowFunction(window_size)
+{
+    for (std::size_t n = 0; n < this->window_size_; n++) {
+        this->cached_factors_[n] = 0;
+        for (unsigned int k = 0; k < a.size(); k++) {
+            this->cached_factors_[n] +=
+                std::pow<double>(-1.0f, k) * a[k] * std::cos(2.0f * (double)M_PI * k * n / this->window_size_);
+        }
+    }
+}
+
+HannWindowFunction::HannWindowFunction(std::size_t window_size)
+    : GeneralizedCosineWindowFunction(window_size, { 0.5f, 0.5f })
+{
+}
+
+HammingWindowFunction::HammingWindowFunction(std::size_t window_size)
+        : GeneralizedCosineWindowFunction(window_size, { 0.53836f, 0.46164f })
+{
+}
+
+BlackmanWindowFunction::BlackmanWindowFunction(std::size_t window_size)
+        : GeneralizedCosineWindowFunction(window_size, { 7938.0f / 18608.0f, 9240.0f / 18608.0f, 1430.0f / 18608.0f })
+{
+}
+
+NuttallWindowFunction::NuttallWindowFunction(std::size_t window_size)
+        : GeneralizedCosineWindowFunction(window_size, { 0.355768f, 0.487396f, 0.144232f, 0.012604f })
+{
+}
\ No newline at end of file
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