[OMPT-svn-commit] SF.net SVN: modplug:[2165] trunk/OpenMPT/soundlib/Snd_fx.cpp

[<sag...@us...>]

Revision: 2165
          http://sourceforge.net/p/modplug/code/2165
Author:   saga-games
Date:     2013-05-21 21:18:58 +0000 (Tue, 21 May 2013)
Log Message:
-----------
[Fix] FT2 compatibility: Also limit period values to 16-bit in Amiga slide mode (not 100% precise yet as it seems, but uh, "close enough", I guess.)

Modified Paths:
--------------
    trunk/OpenMPT/soundlib/Snd_fx.cpp

Modified: trunk/OpenMPT/soundlib/Snd_fx.cpp
===================================================================
--- trunk/OpenMPT/soundlib/Snd_fx.cpp	2013-05-21 21:18:34 UTC (rev 2164)
+++ trunk/OpenMPT/soundlib/Snd_fx.cpp	2013-05-21 21:18:58 UTC (rev 2165)
@@ -4691,17 +4691,23 @@
 		return ((3546895L * 4) << FREQ_FRACBITS) / period;
 	} else if (GetType() == MOD_TYPE_XM)
 	{
+		if(IsCompatibleMode(TRK_FASTTRACKER2))
+		{
+			// FT2 compatibility: Period is a 16-bit value in FT2, and it overflows happily.
+			// Test case: FreqWraparound.xm
+			period &= 0xFFFF;
+		}
 		if(m_SongFlags[SONG_LINEARSLIDES])
 		{
 			uint32 octave = period / 768;
 			if(IsCompatibleMode(TRK_FASTTRACKER2))
 			{
 				// Under normal circumstances, this calculation returns the same values as the non-compatible one.
-				// However, once the 12 octaves are exceeded (through portamento slides), FT2 wraps the frequency around...
+				// However, once the 12 octaves are exceeded (through portamento slides), the octave shift goes
+				// crazy in FT2, meaning that the frequency wraps around randomly...
 				// Test case: FreqWraparound.xm
 				// 12 octaves * (12 * 64) LUT entries = 9216, add 767 for rounding
-				// Period is a 16 bit value in FT2, hence the "& 0xFFFF".
-				uint32 div = ((9216u + 767u - (period & 0xFFFF)) / 768);
+				uint32 div = ((9216u + 767u - period) / 768);
 				octave = ((12 - div) & 0x1F) % 29u;
 			}
 			return (XMLinearTable[period % 768] << FREQ_FRACBITS) >> octave;

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