DSP: Implement audio filters (simple, biquad)

src/audio_core/hle/common.h

@@ -0,0 +1,35 @@
+// Copyright 2016 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <algorithm>
+#include <array>
+
+#include "audio_core/audio_core.h"
+
+#include "common/common_types.h"
+
+namespace DSP {
+namespace HLE {
+
+/// The final output to the speakers is stereo. Preprocessing output in Source is also stereo.
+using StereoFrame16 = std::array<std::array<s16, 2>, AudioCore::samples_per_frame>;
+
+/// The DSP is quadraphonic internally.
+using QuadFrame32   = std::array<std::array<s32, 4>, AudioCore::samples_per_frame>;
+
+/**
+ * This performs the filter operation defined by FilterT::ProcessSample on the frame in-place.
+ * FilterT::ProcessSample is called sequentially on the samples.
+ */
+template<typename FrameT, typename FilterT>
+void FilterFrame(FrameT& frame, FilterT& filter) {
+    std::transform(frame.begin(), frame.end(), frame.begin(), [&filter](const typename FrameT::value_type& sample) {
+        return filter.ProcessSample(sample);
+    });
+}
+
+} // namespace HLE
+} // namespace DSP