Add Karplus-Strong guitar generation algorithm

libs/audio/include/psemek/audio/wave/karplus_strong.hpp

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <psemek/audio/stream.hpp>
+
+namespace psemek::audio
+{
+
+	stream_ptr karplus_strong(float frequency);
+
+}

libs/audio/source/wave/karplus_strong.cpp

@@ -0,0 +1,69 @@
+#include <psemek/audio/wave/karplus_strong.hpp>
+#include <psemek/audio/constants.hpp>
+#include <psemek/random/generator.hpp>
+#include <psemek/random/uniform.hpp>
+
+#include <vector>
+#include <atomic>
+
+namespace psemek::audio
+{
+
+	namespace
+	{
+
+		struct karplus_strong_impl
+			: stream
+		{
+			karplus_strong_impl(float frequency)
+				: buffer_(2 * std::round(audio::frequency / frequency))
+			{
+				random::generator rng{0x4b0a763ef6573bf2ull, 0};
+				for (auto & v : buffer_)
+					v = random::uniform(rng, -1.f, 1.f);
+			}
+
+			std::optional<std::size_t> length() const override
+			{
+				return std::nullopt;
+			}
+
+			std::size_t read(float * data, std::size_t sample_count) override
+			{
+				std::size_t const size = buffer_.size();
+
+				for (std::size_t i = 0; i < sample_count; i += 2)
+				{
+					buffer_[buffer_pos_ + 0] = (buffer_[buffer_pos_ + 0] + buffer_[(buffer_pos_ + 2) % size + 0]) / 2.f;
+					buffer_[buffer_pos_ + 1] = (buffer_[buffer_pos_ + 1] + buffer_[(buffer_pos_ + 2) % size + 1]) / 2.f;
+
+					data[i + 0] = buffer_[buffer_pos_ + 0];
+					data[i + 1] = buffer_[buffer_pos_ + 1];
+
+					buffer_pos_ += 2;
+					buffer_pos_ %= size;
+				}
+
+				return sample_count;
+			}
+
+			std::size_t played() const override
+			{
+				return played_.load();
+			}
+
+		private:
+			std::vector<float> buffer_;
+			std::size_t buffer_pos_{0};
+
+			std::atomic<std::size_t> played_;
+		};
+
+	}
+
+	stream_ptr karplus_strong(float frequency)
+	{
+		return std::make_shared<karplus_strong_impl>(frequency);
+	}
+
+}