DSP: Implement audio codecs (PCM8, PCM16, ADPCM)

src/audio_core/codec.h

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+// Copyright 2016 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <array>
+#include <vector>
+
+#include "common/common_types.h"
+
+namespace Codec {
+
+/// A variable length buffer of signed PCM16 stereo samples.
+using StereoBuffer16 = std::vector<std::array<s16, 2>>;
+
+/// See: Codec::DecodeADPCM
+struct ADPCMState {
+    // Two historical samples from previous processed buffer,
+    // required for ADPCM decoding
+    s16 yn1; ///< y[n-1]
+    s16 yn2; ///< y[n-2]
+};
+
+/**
+ * @param data Pointer to buffer that contains ADPCM data to decode
+ * @param sample_count Length of buffer in terms of number of samples
+ * @param adpcm_coeff ADPCM coefficients
+ * @param state ADPCM state, this is updated with new state
+ * @return Decoded stereo signed PCM16 data, sample_count in length
+ */
+StereoBuffer16 DecodeADPCM(const u8* const data, const size_t sample_count, const std::array<s16, 16>& adpcm_coeff, ADPCMState& state);
+
+/**
+ * @param num_channels Number of channels
+ * @param data Pointer to buffer that contains PCM8 data to decode
+ * @param sample_count Length of buffer in terms of number of samples
+ * @return Decoded stereo signed PCM16 data, sample_count in length
+ */
+StereoBuffer16 DecodePCM8(const unsigned num_channels, const u8* const data, const size_t sample_count);
+
+/**
+ * @param num_channels Number of channels
+ * @param data Pointer to buffer that contains PCM16 data to decode
+ * @param sample_count Length of buffer in terms of number of samples
+ * @return Decoded stereo signed PCM16 data, sample_count in length
+ */
+StereoBuffer16 DecodePCM16(const unsigned num_channels, const u8* const data, const size_t sample_count);
+
+};