decoder/mpcdec: fix replay gain formula with v8

"When playing musepack files with mpd v0.15.8, rg seems to have no effect. Using sample file below, mpd says 'computing ReplayGain album scale with gain 122.879997, peak 0.549150'. One thing though, if I build mpd against old libmpcdec-1.2.6, rg works as expected: 'computing ReplayGain album scale with gain 16.820000, peak 0.099765'"

decoder/mpcdec: fix replay gain formula with v8
73ba4ea3 · Aleksei Kaveshnikov · Max Kellermann · cbfaa4a2 · 73ba4ea3 · 73ba4ea3
Commit 73ba4ea3 authored Mar 12, 2010 by Aleksei Kaveshnikov Committed by Max Kellermann Mar 19, 2010
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NEWS NEWS +1 -0

mpcdec_plugin.c src/decoder/mpcdec_plugin.c +8 -0

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--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,7 @@ ver 0.15.9 (2009/??/??)
 * decoders:
  - mad: fix crash when seeking at end of song
  - mpcdec: fix negative shift on fixed-point samples
+  - mpcdec: fix replay gain formula with v8
 * playlist: fix single+repeat in random mode
 * player: postpone song tags during cross-fade


--- a/src/decoder/mpcdec_plugin.c
+++ b/src/decoder/mpcdec_plugin.c
@@ -24,6 +24,7 @@
 #include <mpcdec/mpcdec.h>
 #else
 #include <mpc/mpcdec.h>
+#include <math.h>
 #endif

 #include <glib.h>
@@ -209,10 +210,17 @@ mpcdec_decode(struct decoder *mpd_decoder, struct input_stream *is)
 	}

 	replay_gain_info = replay_gain_info_new();
+#ifdef MPC_IS_OLD_API
 	replay_gain_info->tuples[REPLAY_GAIN_ALBUM].gain = info.gain_album * 0.01;
 	replay_gain_info->tuples[REPLAY_GAIN_ALBUM].peak = info.peak_album / 32767.0;
 	replay_gain_info->tuples[REPLAY_GAIN_TRACK].gain = info.gain_title * 0.01;
 	replay_gain_info->tuples[REPLAY_GAIN_TRACK].peak = info.peak_title / 32767.0;
+#else
+	replay_gain_info->tuples[REPLAY_GAIN_ALBUM].gain = MPC_OLD_GAIN_REF  - (info.gain_album  / 256.);
+	replay_gain_info->tuples[REPLAY_GAIN_ALBUM].peak = pow(10, info.peak_album / 256. / 20) / 32767;
+	replay_gain_info->tuples[REPLAY_GAIN_TRACK].gain = MPC_OLD_GAIN_REF  - (info.gain_title  / 256.);
+	replay_gain_info->tuples[REPLAY_GAIN_TRACK].peak = pow(10, info.peak_title / 256. / 20) / 32767;
+#endif

 	decoder_initialized(mpd_decoder, &audio_format,
 			    is->seekable,