Add emulation of the FT2 pattern loop bug.

One of the most (in)famous FT2 bugs is the E60 bug: When E60 is used on
a pattern row x, the following pattern also starts from row x instead of
the beginning of the pattern. This can be avoided by placing a D00
pattern break on the last row of the pattern where E60 was used.

Described here: http://www.milkytracker.org/docs/MilkyTracker.html#fxE6x

Test tune:
http://api.modarchive.org/downloads.php?moduleid=55647#roadblas.xm

src/libmodplug/sndfile.h

@@ -578,7 +578,7 @@ class MODPLUG_EXPORT CSoundFile
 	UINT m_nType, m_nSamples, m_nInstruments;
 	UINT m_nTickCount, m_nTotalCount, m_nPatternDelay, m_nFrameDelay;
 	UINT m_nMusicSpeed, m_nMusicTempo;
-	UINT m_nNextRow, m_nRow;
+	UINT m_nNextRow, m_nRow, m_nNextStartRow;
 	UINT m_nPattern,m_nCurrentPattern,m_nNextPattern,m_nRestartPos;
 	UINT m_nMasterVolume, m_nGlobalVolume, m_nSongPreAmp;
 	UINT m_nFreqFactor, m_nTempoFactor, m_nOldGlbVolSlide;

src/snd_fx.cpp

@@ -21,7 +21,7 @@ DWORD CSoundFile::GetLength(BOOL bAdjust, BOOL bTotal)
 {
 	UINT dwElapsedTime=0, nRow=0, nCurrentPattern=0, nNextPattern=0, nPattern=0;
 	UINT nMusicSpeed=m_nDefaultSpeed, nMusicTempo=m_nDefaultTempo, nNextRow=0;
-	UINT nMaxRow = 0, nMaxPattern = 0;
+	UINT nMaxRow = 0, nMaxPattern = 0, nNextStartRow = 0;
 	LONG nGlbVol = m_nDefaultGlobalVolume, nOldGlbVolSlide = 0;
 	BYTE samples[MAX_CHANNELS];
 	BYTE instr[MAX_CHANNELS];
@@ -71,7 +71,8 @@ DWORD CSoundFile::GetLength(BOOL bAdjust, BOOL bTotal)
 		if (nNextRow >= PatternSize[nPattern])
 		{
 			nNextPattern = nCurrentPattern + 1;
-			nNextRow = 0;
+			nNextRow = nNextStartRow;
+			nNextStartRow = 0;
 		}
 		if (!nRow)
 		{
@@ -106,6 +107,7 @@ DWORD CSoundFile::GetLength(BOOL bAdjust, BOOL bTotal)
 				if (param <= nCurrentPattern) goto EndMod;
 				nNextPattern = param;
 				nNextRow = 0;
+				nNextStartRow = 0;
 				if (bAdjust)
 				{
 					pChn->nPatternLoopCount = 0;
@@ -116,6 +118,7 @@ DWORD CSoundFile::GetLength(BOOL bAdjust, BOOL bTotal)
 			case CMD_PATTERNBREAK:
 				nNextRow = param;
 				nNextPattern = nCurrentPattern + 1;
+				nNextStartRow = 0;
 				if (bAdjust)
 				{
 					pChn->nPatternLoopCount = 0;
@@ -157,7 +160,10 @@ DWORD CSoundFile::GetLength(BOOL bAdjust, BOOL bTotal)
 				if ((param & 0xF0) == 0x60)
 				{
 					if (param & 0x0F) dwElapsedTime += (dwElapsedTime - patloop[nChn]) * (param & 0x0F);
-					else patloop[nChn] = dwElapsedTime;
+					else {
+						patloop[nChn] = dwElapsedTime;
+						if (m_nType & MOD_TYPE_XM) nNextStartRow = nRow;
+					}
 				}
 				break;
 			}
@@ -1169,11 +1175,13 @@ BOOL CSoundFile::ProcessEffects()
 		// Position Jump
 		case CMD_POSITIONJUMP:
 			nPosJump = param;
+			m_nNextStartRow = 0;
 			break;
 
 		// Pattern Break
 		case CMD_PATTERNBREAK:
 			nBreakRow = param;
+			m_nNextStartRow = 0;
 			break;
 
 		// Midi Controller
@@ -2127,6 +2135,7 @@ int CSoundFile::PatternLoop(MODCHANNEL *pChn, UINT param)
 	} else
 	{
 		pChn->nPatternLoop = m_nRow;
+		if (m_nType & MOD_TYPE_XM) m_nNextStartRow = m_nRow;
 	}
 	return -1;
 }

src/sndfile.cpp

@@ -103,6 +103,7 @@ BOOL CSoundFile::Create(LPCBYTE lpStream, DWORD dwMemLength)
 	m_nFrameDelay = 0;
 	m_nNextRow = 0;
 	m_nRow = 0;
+	m_nNextStartRow = 0;
 	m_nPattern = 0;
 	m_nCurrentPattern = 0;
 	m_nNextPattern = 0;
@@ -244,6 +245,7 @@ BOOL CSoundFile::Create(LPCBYTE lpStream, DWORD dwMemLength)
 	m_nTickCount = m_nMusicSpeed;
 	m_nNextRow = 0;
 	m_nRow = 0;
+	m_nNextStartRow = 0;
 	if ((m_nRestartPos >= MAX_ORDERS) || (Order[m_nRestartPos] >= MAX_PATTERNS)) m_nRestartPos = 0;
 	// Load plugins
 	if (gpMixPluginCreateProc)
@@ -678,6 +680,7 @@ void CSoundFile::SetCurrentPos(UINT nPos)
 	}
 	m_nNextPattern = nPattern;
 	m_nNextRow = nRow;
+	m_nNextStartRow = 0;
 	m_nTickCount = m_nMusicSpeed;
 	m_nBufferCount = 0;
 	m_nPatternDelay = 0;
@@ -706,7 +709,7 @@ void CSoundFile::SetCurrentOrder(UINT nPos)
 	} else
 	{
 		m_nNextPattern = nPos;
-		m_nRow = m_nNextRow = 0;
+		m_nRow = m_nNextRow = m_nNextStartRow = 0;
 		m_nPattern = 0;
 		m_nTickCount = m_nMusicSpeed;
 		m_nBufferCount = 0;

src/sndmix.cpp

@@ -419,7 +419,8 @@ BOOL CSoundFile::ProcessRow()
 		if (m_nNextRow >= PatternSize[m_nPattern])
 		{
 			if (!(m_dwSongFlags & SONG_PATTERNLOOP)) m_nNextPattern = m_nCurrentPattern + 1;
-			m_nNextRow = 0;
+			m_nNextRow = m_nNextStartRow;
+			m_nNextStartRow = 0;
 		}
 		// Reset channel values
 		MODCHANNEL *pChn = Chn;