DecoderAPI: use std::chrono::duration for decoder_seek*()

For type safety and code readability.

Makefile.am

@@ -178,6 +178,7 @@ libmpd_a_SOURCES = \
 	src/TagStream.cxx src/TagStream.hxx \
 	src/TimePrint.cxx src/TimePrint.hxx \
 	src/mixer/Volume.cxx src/mixer/Volume.hxx \
+	src/Chrono.hxx \
 	src/SongFilter.cxx src/SongFilter.hxx \
 	src/PlaylistFile.cxx src/PlaylistFile.hxx
 

src/Chrono.hxx

@@ -0,0 +1,66 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_CHRONO_HXX
+#define MPD_CHRONO_HXX
+
+#include <chrono>
+#include <cstdint>
+
+/**
+ * A time stamp within a song.  Granularity is 1 millisecond and the
+ * maximum value is about 49 days.
+ */
+class SongTime : public std::chrono::duration<std::uint32_t, std::milli> {
+	typedef std::chrono::duration<std::uint32_t, std::milli> Base;
+	typedef Base::rep rep;
+
+public:
+	SongTime() = default;
+
+	template<typename T>
+	explicit constexpr SongTime(T t):Base(t) {}
+
+	static constexpr SongTime FromS(unsigned s) {
+		return SongTime(rep(s) * 1000);
+	}
+
+	static constexpr SongTime FromS(float s) {
+		return SongTime(rep(s * 1000));
+	}
+
+	static constexpr SongTime FromS(double s) {
+		return SongTime(rep(s * 1000));
+	}
+
+	static constexpr SongTime FromMS(rep ms) {
+		return SongTime(ms);
+	}
+
+	constexpr rep ToMS() const {
+		return count();
+	}
+
+	constexpr unsigned ToScale(unsigned base) const {
+		// TODO: case to 64 bit to avoid integer overflow?
+		return count() * base / 1000;
+	}
+};
+
+#endif

src/decoder/DecoderAPI.cxx

@@ -204,37 +204,21 @@ decoder_command_finished(Decoder &decoder)
 	dc.Unlock();
 }
 
-double decoder_seek_where(gcc_unused Decoder & decoder)
+SongTime
+decoder_seek_time(Decoder &decoder)
 {
 	const DecoderControl &dc = decoder.dc;
 
 	assert(dc.pipe != nullptr);
 
 	if (decoder.initial_seek_running)
-		return dc.start_ms / 1000.;
+		return SongTime(dc.start_ms);
 
 	assert(dc.command == DecoderCommand::SEEK);
 
 	decoder.seeking = true;
 
-	return dc.seek_where;
+	return SongTime::FromS(dc.seek_where);
-}
-
-unsigned
-decoder_seek_where_ms(Decoder &decoder)
-{
-	const DecoderControl &dc = decoder.dc;
-
-	assert(dc.pipe != nullptr);
-
-	if (decoder.initial_seek_running)
-		return dc.start_ms;
-
-	assert(dc.command == DecoderCommand::SEEK);
-
-	decoder.seeking = true;
-
-	return unsigned(dc.seek_where * 1000);
 }
 
 uint64_t

src/decoder/DecoderAPI.hxx

@@ -37,6 +37,7 @@
 #include "AudioFormat.hxx"
 #include "MixRampInfo.hxx"
 #include "config/ConfigData.hxx"
+#include "Chrono.hxx"
 
 // IWYU pragma: end_exports
 
@@ -80,16 +81,6 @@ decoder_get_command(Decoder &decoder);
 void
 decoder_command_finished(Decoder &decoder);
 
-/**
- * Call this when you have received the DecoderCommand::SEEK command.
- *
- * @param decoder the decoder object
- * @return the destination position for the week
- */
-gcc_pure
-double
-decoder_seek_where(Decoder &decoder);
-
 /**
  * Call this when you have received the DecoderCommand::SEEK command.
  *
@@ -97,8 +88,8 @@ decoder_seek_where(Decoder &decoder);
  * @return the destination position for the seek in milliseconds
  */
 gcc_pure
-unsigned
+SongTime
-decoder_seek_where_ms(Decoder &decoder);
+decoder_seek_time(Decoder &decoder);
 
 /**
  * Call this when you have received the DecoderCommand::SEEK command.

src/decoder/plugins/FfmpegDecoderPlugin.cxx

@@ -210,11 +210,19 @@ time_from_ffmpeg(int64_t t, const AVRational time_base)
 		/ (double)1024;
 }
 
+template<typename Ratio>
+static constexpr AVRational
+RatioToAVRational()
+{
+	return { Ratio::num, Ratio::den };
+}
+
 gcc_const
 static int64_t
-time_to_ffmpeg(double t_ms, const AVRational time_base)
+time_to_ffmpeg(SongTime t, const AVRational time_base)
 {
-	return av_rescale_q(t_ms, (AVRational){1, 1000},
+	return av_rescale_q(t.count(),
+			    RatioToAVRational<SongTime::period>(),
 			    time_base);
 }
 
@@ -547,7 +555,7 @@ ffmpeg_decode(Decoder &decoder, InputStream &input)
 
 		if (cmd == DecoderCommand::SEEK) {
 			int64_t where =
-				time_to_ffmpeg(decoder_seek_where_ms(decoder),
+				time_to_ffmpeg(decoder_seek_time(decoder),
 					       av_stream->time_base) +
 				start_time_fallback(*av_stream);
 

src/decoder/plugins/GmeDecoderPlugin.cxx

@@ -194,7 +194,7 @@ gme_file_decode(Decoder &decoder, Path path_fs)
 
 		cmd = decoder_data(decoder, nullptr, buf, sizeof(buf), 0);
 		if (cmd == DecoderCommand::SEEK) {
-			unsigned where = decoder_seek_where_ms(decoder);
+			unsigned where = decoder_seek_time(decoder).ToMS();
 			gme_err = gme_seek(emu, where);
 			if (gme_err != nullptr)
 				LogWarning(gme_domain, gme_err);

src/decoder/plugins/MadDecoderPlugin.cxx

@@ -67,6 +67,13 @@ static constexpr Domain mad_domain("mad");
 
 static bool gapless_playback;
 
+gcc_const
+static SongTime
+ToSongTime(mad_timer_t t)
+{
+	return SongTime::FromMS(mad_timer_count(t, MAD_UNITS_MILLISECONDS));
+}
+
 static inline int32_t
 mad_fixed_to_24_sample(mad_fixed_t sample)
 {
@@ -116,8 +123,8 @@ struct MadDecoder {
 	unsigned char input_buffer[READ_BUFFER_SIZE];
 	int32_t output_buffer[MP3_DATA_OUTPUT_BUFFER_SIZE];
 	float total_time;
-	unsigned elapsed_time;
+	SongTime elapsed_time;
-	unsigned seek_where;
+	SongTime seek_time;
 	enum muteframe mute_frame;
 	long *frame_offsets;
 	mad_timer_t *times;
@@ -159,7 +166,7 @@ struct MadDecoder {
 	bool DecodeFirstFrame(Tag **tag);
 
 	gcc_pure
-	long TimeToFrame(unsigned t) const;
+	long TimeToFrame(SongTime t) const;
 
 	void UpdateTimerNextFrame();
 
@@ -847,13 +854,12 @@ mad_decoder_total_file_time(InputStream &is)
 }
 
 long
-MadDecoder::TimeToFrame(unsigned t) const
+MadDecoder::TimeToFrame(SongTime t) const
 {
 	unsigned long i;
 
 	for (i = 0; i < highest_frame; ++i) {
-		unsigned frame_time =
+		auto frame_time = ToSongTime(times[i]);
-			mad_timer_count(times[i], MAD_UNITS_MILLISECONDS);
 		if (frame_time >= t)
 			break;
 	}
@@ -884,7 +890,7 @@ MadDecoder::UpdateTimerNextFrame()
 		timer = times[current_frame];
 
 	current_frame++;
-	elapsed_time = mad_timer_count(timer, MAD_UNITS_MILLISECONDS);
+	elapsed_time = ToSongTime(timer);
 }
 
 DecoderCommand
@@ -980,7 +986,7 @@ MadDecoder::Read()
 		mute_frame = MUTEFRAME_NONE;
 		break;
 	case MUTEFRAME_SEEK:
-		if (elapsed_time >= seek_where)
+		if (elapsed_time >= seek_time)
 			mute_frame = MUTEFRAME_NONE;
 		break;
 	case MUTEFRAME_NONE:
@@ -989,7 +995,7 @@ MadDecoder::Read()
 			assert(input_stream.IsSeekable());
 
 			unsigned long j =
-				TimeToFrame(decoder_seek_where_ms(*decoder));
+				TimeToFrame(decoder_seek_time(*decoder));
 			if (j < highest_frame) {
 				if (Seek(frame_offsets[j])) {
 					current_frame = j;
@@ -997,7 +1003,7 @@ MadDecoder::Read()
 				} else
 					decoder_seek_error(*decoder);
 			} else {
-				seek_where = decoder_seek_where_ms(*decoder);
+				seek_time = decoder_seek_time(*decoder);
 				mute_frame = MUTEFRAME_SEEK;
 				decoder_command_finished(*decoder);
 			}

src/decoder/plugins/ModplugDecoderPlugin.cxx

@@ -166,7 +166,7 @@ mod_decode(Decoder &decoder, InputStream &is)
 				   0);
 
 		if (cmd == DecoderCommand::SEEK) {
-			ModPlug_Seek(f, decoder_seek_where_ms(decoder));
+			ModPlug_Seek(f, decoder_seek_time(decoder).ToMS());
 			decoder_command_finished(decoder);
 		}
 

src/decoder/plugins/Mp4v2DecoderPlugin.cxx

@@ -165,9 +165,8 @@ mp4_file_decode(Decoder &mpd_decoder, Path path_fs)
 		unsigned int data_length = 0;
 
 		if (cmd == DecoderCommand::SEEK) {
-			const unsigned offset_ms =
+			const MP4Timestamp offset =
-				decoder_seek_where_ms(mpd_decoder);
+				decoder_seek_time(mpd_decoder).ToScale(scale);
-			const MP4Timestamp offset = (offset_ms * scale) / 1000;
 
 			sample = MP4GetSampleIdFromTime(handle, track, offset,
 							false);

src/decoder/plugins/SidplayDecoderPlugin.cxx

@@ -314,8 +314,8 @@ sidplay_file_decode(Decoder &decoder, Path path_fs)
 
 		if (cmd == DecoderCommand::SEEK) {
 			unsigned data_time = player.time();
-			unsigned target_time = (unsigned)
+			unsigned target_time =
-				(decoder_seek_where(decoder) * timebase);
+				decoder_seek_time(decoder).ToScale(timebase);
 
 			/* can't rewind so return to zero and seek forward */
 			if(target_time<data_time) {

test/FakeDecoderAPI.cxx

@@ -55,16 +55,10 @@ decoder_command_finished(gcc_unused Decoder &decoder)
 {
 }
 
-double
+SongTime
-decoder_seek_where(gcc_unused Decoder &decoder)
+decoder_seek_time(gcc_unused Decoder &decoder)
 {
-	return 1.0;
+	return SongTime();
-}
-
-unsigned
-decoder_seek_where_ms(gcc_unused Decoder &decoder)
-{
-	return 1;
 }
 
 uint64_t