From 0e266d73f9aab89410c736e969eaa51ef914acf1 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Wed, 20 Jun 2018 13:33:20 +0300
Subject: [PATCH] Add support for MP3 files using libmad

---
 Build                   |   2 +
 source/mp3decoder.cpp   | 160 ++++++++++++++++++++++++++++++++++++++++
 source/mp3decoder.h     |  49 ++++++++++++
 source/sounddecoder.cpp |   3 +
 4 files changed, 214 insertions(+)
 create mode 100644 source/mp3decoder.cpp
 create mode 100644 source/mp3decoder.h

diff --git a/Build b/Build
index 4517ad5..02ebe32 100644
--- a/Build
+++ b/Build
@@ -3,7 +3,9 @@ package "mspal"
 	version "0.10";
 	description "C++ wrapper for OpenAL";
 
+	// TODO make these features
 	require "vorbisfile";
+	require "mad";
 	require "openal";
 	require "sigc++-2.0";
 	require "mspcore";
diff --git a/source/mp3decoder.cpp b/source/mp3decoder.cpp
new file mode 100644
index 0000000..a717cf4
--- /dev/null
+++ b/source/mp3decoder.cpp
@@ -0,0 +1,160 @@
+#include <limits>
+#include <mad.h>
+#include <msp/strings/format.h>
+#include "mp3decoder.h"
+
+using namespace std;
+
+namespace {
+
+Msp::Int16 scale(mad_fixed_t sample)
+{
+	if(sample<=-MAD_F_ONE)
+		return numeric_limits<Msp::Int16>::min();
+	else if(sample>=MAD_F_ONE)
+		return numeric_limits<Msp::Int16>::max();
+	else
+		return (sample + (1<<(MAD_F_FRACBITS-16))) >> (MAD_F_FRACBITS-15);
+}
+
+} // namespace
+
+
+namespace Msp {
+namespace AL {
+
+mp3_error::mp3_error(const std::string &func, int err):
+	runtime_error(format("%s: %s", func, get_message(err)))
+{ }
+
+string mp3_error::get_message(int err)
+{
+	return format("%d", err);
+}
+
+
+struct Mp3Decoder::Private
+{
+	mad_stream stream;
+	mad_frame frame;
+	mad_synth synth;
+};
+
+
+Mp3Decoder::Mp3Decoder(IO::Seekable &io):
+	priv(new Private),
+	in(io),
+	in_buf_size(16384),
+	in_buffer(new char[in_buf_size]),
+	read_pos(0)
+{
+	mad_stream_init(&priv->stream);
+	mad_frame_init(&priv->frame);
+	mad_synth_init(&priv->synth);
+
+	try
+	{
+		decode_frame();
+		format = (priv->frame.header.mode==MAD_MODE_SINGLE_CHANNEL ? MONO16 : STEREO16);
+		freq = priv->frame.header.samplerate;
+	}
+	catch(...)
+	{
+		delete[] in_buffer;
+		throw;
+	}
+}
+
+Mp3Decoder::~Mp3Decoder()
+{
+	delete[] in_buffer;
+	mad_synth_finish(&priv->synth);
+	mad_frame_finish(&priv->frame);
+	mad_stream_finish(&priv->stream);
+}
+
+bool Mp3Decoder::detect(const string &sig)
+{
+	if(sig.size()>=2 && sig[0]=='\xFF' && (sig[1]&0xE0)==0xE0)
+		return true;
+
+	static const char id3_sig[] = { 'I', 'D', '3' };
+	if(sig.size()<sizeof(id3_sig))
+		return false;
+	return !sig.compare(0, sizeof(id3_sig), id3_sig);
+}
+
+void Mp3Decoder::rewind()
+{
+	in.seek(0, IO::S_BEG);
+}
+
+unsigned Mp3Decoder::read(char *buf, unsigned len)
+{
+	unsigned nchan = (format==STEREO16 ? 2 : 1);
+	mad_pcm &pcm = priv->synth.pcm;
+
+	unsigned pos = 0;
+	while(pos+2*nchan<=len)
+	{
+		if(read_pos>=pcm.length)
+		{
+			if(!decode_frame())
+				break;
+		}
+
+		for(unsigned i=0; i<nchan; ++i)
+		{
+			Int16 sample = scale(pcm.samples[i][read_pos]);
+			buf[pos++] = sample;
+			buf[pos++] = sample>>8;
+		}
+
+		++read_pos;
+	}
+
+	return pos;
+}
+
+bool Mp3Decoder::fill_input()
+{
+	unsigned in_pos = 0;
+	if(priv->stream.next_frame && priv->stream.next_frame<priv->stream.bufend)
+	{
+		copy(priv->stream.next_frame, priv->stream.bufend, in_buffer);
+		in_pos = priv->stream.bufend-priv->stream.next_frame;
+	}
+
+	unsigned len = in.read(in_buffer+in_pos, in_buf_size-in_pos);
+	in_pos += len;
+
+	mad_stream_buffer(&priv->stream, reinterpret_cast<unsigned char *>(in_buffer), in_pos);
+	priv->stream.error = MAD_ERROR_NONE;
+
+	return len;
+}
+
+bool Mp3Decoder::decode_frame()
+{
+	while(1)
+	{
+		if(!priv->stream.buffer || priv->stream.error==MAD_ERROR_BUFLEN)
+			if(!fill_input())
+				return false;
+
+		if(!mad_frame_decode(&priv->frame, &priv->stream))
+		{
+			mad_synth_frame(&priv->synth, &priv->frame);
+			read_pos = 0;
+			return true;
+		}
+
+		if(priv->stream.error==MAD_ERROR_BUFLEN)
+			continue;
+		else if(!MAD_RECOVERABLE(priv->stream.error))
+			throw mp3_error("mad_frame_decode", priv->stream.error);
+	}
+}
+
+} // namespace AL
+} // namespace Msp
diff --git a/source/mp3decoder.h b/source/mp3decoder.h
new file mode 100644
index 0000000..06060de
--- /dev/null
+++ b/source/mp3decoder.h
@@ -0,0 +1,49 @@
+#ifndef MSP_AL_MP3DECODER_H_
+#define MSP_AL_MP3DECODER_H_
+
+#include <stdexcept>
+#include "sounddecoder.h"
+
+namespace Msp {
+namespace AL {
+
+class mp3_error: public std::runtime_error
+{
+public:
+	mp3_error(const std::string &, int);
+	virtual ~mp3_error() throw() { }
+
+private:
+	static std::string get_message(int);
+};
+
+
+class Mp3Decoder: public SoundDecoder
+{
+private:
+	struct Private;
+
+	Private *priv;
+	IO::Seekable &in;
+	unsigned in_buf_size;
+	char *in_buffer;
+	unsigned read_pos;
+
+public:
+	Mp3Decoder(IO::Seekable &);
+	virtual ~Mp3Decoder();
+
+	static bool detect(const std::string &);
+
+	virtual void rewind();
+	virtual unsigned read(char *, unsigned);
+
+private:
+	bool fill_input();
+	bool decode_frame();
+};
+
+} // namespace AL
+} // namespace Msp
+
+#endif
diff --git a/source/sounddecoder.cpp b/source/sounddecoder.cpp
index a2cd51a..38ae8fa 100644
--- a/source/sounddecoder.cpp
+++ b/source/sounddecoder.cpp
@@ -1,6 +1,7 @@
 #include <msp/core/refptr.h>
 #include <msp/io/file.h>
 #include <msp/strings/format.h>
+#include "mp3decoder.h"
 #include "oggdecoder.h"
 #include "sounddecoder.h"
 
@@ -42,6 +43,8 @@ SoundDecoder *SoundDecoder::open_io(IO::Seekable &io)
 	string signature(sig_buf, sizeof(sig_buf));
 	if(OggDecoder::detect(signature))
 		return new OggDecoder(io);
+	else if(Mp3Decoder::detect(signature))
+		return new Mp3Decoder(io);
 	else
 	{
 		string sig_hex;
-- 
2.43.0