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audio/decoders/g711.cpp

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+/* ScummVM - Graphic Adventure Engine
+ *
+ * ScummVM is the legal property of its developers, whose names
+ * are too numerous to list here. Please refer to the COPYRIGHT
+ * file distributed with this source distribution.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "audio/decoders/g711.h"
+
+#include "audio/audiostream.h"
+#include "common/stream.h"
+#include "common/util.h"
+
+/* from g711.c by SUN microsystems (unrestricted use) */
+
+#define         SIGN_BIT        (0x80)      /* Sign bit for a A-law byte. */
+#define         QUANT_MASK      (0xf)       /* Quantization field mask. */
+#define         SEG_SHIFT       (4)         /* Left shift for segment number. */
+#define         SEG_MASK        (0x70)      /* Segment field mask. */
+#define         BIAS            (0x84)      /* Bias for linear code. */
+
+namespace Audio {
+
+/**
+ * Logarithmic PCM (G.711)
+ * https://en.wikipedia.org/wiki/G.711
+ * https://wiki.multimedia.cx/index.php/PCM#Logarithmic_PCM
+ */
+class G711AudioStream : public SeekableAudioStream {
+	Common::DisposablePtr<Common::SeekableReadStream> _stream;
+	const int _rate;
+	const int _channels;
+
+protected:
+	virtual int16 decodeSample(uint8 val) = 0;
+
+public:
+	G711AudioStream(Common::SeekableReadStream *stream, DisposeAfterUse::Flag disposeAfterUse, int rate, int channels) :
+		_stream(stream, disposeAfterUse),
+		_rate(rate),
+		_channels(channels) {
+	}
+
+	int readBuffer(int16 *buffer, const int numSamples) override {
+		int samples;
+
+		for (samples = 0; samples < numSamples; samples++) {
+			uint8 val = _stream->readByte();
+			if (endOfData())
+				break;
+			buffer[samples] = decodeSample(val);
+		}
+
+		return samples;
+	}
+
+	bool isStereo() const override { return (_channels == 2); }
+	int getRate() const override { return _rate; }
+	bool endOfData() const override { return _stream->eos(); }
+	bool seek(const Timestamp &where) override {
+		const uint32 seekSample = convertTimeToStreamPos(where, getRate(), isStereo()).totalNumberOfFrames();
+		return _stream->seek(seekSample, SEEK_SET);
+	}
+	Timestamp getLength() const override {
+		return Timestamp(0, _stream->size() / _channels, _rate);
+	}
+};
+
+class G711ALawStream : public G711AudioStream {
+	int16 decodeSample(uint8 val) override {
+		val ^= 0x55;
+
+		int t = val & QUANT_MASK;
+		int seg = ((unsigned)val & SEG_MASK) >> SEG_SHIFT;
+		if (seg)
+			t = (t + t + 1 + 32) << (seg + 2);
+		else
+			t = (t + t + 1) << 3;
+
+		return (val & SIGN_BIT) ? t : -t;
+	}
+	
+public:
+	G711ALawStream(Common::SeekableReadStream *stream, DisposeAfterUse::Flag disposeAfterUse, int rate, int channels) :
+		G711AudioStream(stream, disposeAfterUse, rate, channels) {
+	}
+};
+
+SeekableAudioStream *makeALawStream(Common::SeekableReadStream *stream, DisposeAfterUse::Flag disposeAfterUse, int rate, int channels) {
+	return new G711ALawStream(stream, disposeAfterUse, rate, channels);
+}
+
+class G711MuLawStream : public G711AudioStream {
+	int16 decodeSample(uint8 val) override {
+		val = ~val;
+
+		int t = ((val & QUANT_MASK) << 3) + BIAS;
+		t <<= ((unsigned)val & SEG_MASK) >> SEG_SHIFT;
+
+		return (val & SIGN_BIT) ? (BIAS - t) : (t - BIAS);
+	}
+	
+public:
+	G711MuLawStream(Common::SeekableReadStream *stream, DisposeAfterUse::Flag disposeAfterUse, int rate, int channels) :
+		G711AudioStream(stream, disposeAfterUse, rate, channels) {
+	}
+};
+
+SeekableAudioStream *makeMuLawStream(Common::SeekableReadStream *stream, DisposeAfterUse::Flag disposeAfterUse, int rate, int channels) {
+	return new G711MuLawStream(stream, disposeAfterUse, rate, channels);
+}
+
+} // End of namespace Audio