the relevant part

TestTimingData.cpp

enum
{
	FOUND_WARP,
	FOUND_WARP_DESTINATION,
	FOUND_BPM_CHANGE,
	FOUND_STOP,
	FOUND_MARKER,
	NOT_FOUND
};

void TimingData::GetBeatAndBPSFromElapsedTimeNoOffset( float fElapsedTime, float &fBeatOut, float &fBPSOut, bool &bFreezeOut, bool &bDelayOut, int &iWarpBeginOut, float &fWarpLengthOut ) const
{
	
	vector<BPMSegment>::const_iterator  itBPMS = m_BPMSegments.begin();
	vector<WarpSegment>::const_iterator itWS   = m_WarpSegments.begin();
	vector<StopSegment>::const_iterator itSS   = m_StopSegments.begin();
	
	// these vector must already be sorted
	// maybe go through these vectors one time to see if it's really sorted

	int iLastRow = 0;
	float fLastTime = -m_fBeat0OffsetInSeconds;
	float fBPS = GetBPMAtRow(0) / 60.0;
	
	float bIsWarping = false;
	float fWarpDestination = 0.0;
	
	for( ;; )
	{
		int iEventRow = INT_MAX;
		int iEventType = NOT_FOUND;
		if( bIsWarping && BeatToNoteRow(fWarpDestination) < iEventRow )
		{
			iEventRow = BeatToNoteRow(fWarpDestination);
			iEventType = FOUND_WARP_DESTINATION;
		}
		if( itWS != m_WarpSegments.end() && itWS->m_iStartRow < iEventRow )
		{
			iEventRow = itWS->m_iStartRow;
			iEventType = FOUND_WARP;
		}
		if( itBPMS != m_BPMSegments.end() && itBPMS->m_iStartRow < iEventRow )
		{
			iEventRow = itBPMS->m_iStartRow;
			iEventType = FOUND_BPM_CHANGE;
		}
		if( itSS != m_StopSegments.end() && itSS->m_iStartRow < iEventRow )
		{
			iEventRow = itSS->m_iStartRow;
			iEventType = FOUND_STOP;
		}
		if( iEventType == NOT_FOUND )
		{
			break;
		}
		float fTimeToNextEvent = bIsWarping ? 0 : NoteRowToBeat( iEventRow - iLastRow ) / fBPS;
		float fNextEventTime   = fLastTime + fTimeToNextEvent;
		if ( fElapsedTime < fNextEventTime )
		{
			break;
		}
		fLastTime = fNextEventTime;
		switch( iEventType )
		{
		case FOUND_WARP_DESTINATION:
			bIsWarping = false;
			break;
		case FOUND_WARP:
			bIsWarping = true;
			if( itWS->m_fEndBeat > fWarpDestination )
			{
				fWarpDestination = itWS->m_fEndBeat;
			}
			itWS ++;
			break;
		case FOUND_BPM_CHANGE:
			fBPS = itBPMS->m_fBPS;
			itBPMS ++;
			break;
		case FOUND_STOP:
			fTimeToNextEvent = bIsWarping ? 0 : itSS->m_fStopSeconds;
			fNextEventTime   = fLastTime + fTimeToNextEvent;
			const bool bIsDelay = itSS->m_bDelay;
			if ( fElapsedTime < fNextEventTime )
			{
				bFreezeOut = !bIsDelay;
				bDelayOut  = bIsDelay;
				fBeatOut   = NoteRowToBeat( itSS->m_iStartRow );
				fBPSOut    = fBPS;
				return;
			}
			fLastTime = fNextEventTime;
			itSS ++;
			break;
		}
		iLastRow = iEventRow;
	}
	
	fBeatOut = NoteRowToBeat( iLastRow ) + (fElapsedTime - fLastTime) * fBPS;
	fBPSOut = fBPS;
	
}

float TimingData::GetElapsedTimeFromBeatNoOffset( float fBeat ) const
{

	vector<BPMSegment>::const_iterator  itBPMS = m_BPMSegments.begin();
	vector<WarpSegment>::const_iterator itWS   = m_WarpSegments.begin();
	vector<StopSegment>::const_iterator itSS   = m_StopSegments.begin();
	
	int iLastRow = 0;
	float fLastTime = -m_fBeat0OffsetInSeconds;
	float fBPS = GetBPMAtRow(0) / 60.0;
	
	float bIsWarping = false;
	float fWarpDestination = 0.0;
	
	for( ;; )
	{
		int iEventRow = INT_MAX;
		int iEventType = NOT_FOUND;
		if( bIsWarping && BeatToNoteRow(fWarpDestination) < iEventRow )
		{
			iEventRow = BeatToNoteRow(fWarpDestination);
			iEventType = FOUND_WARP_DESTINATION;
		}
		if( itWS != m_WarpSegments.end() && itWS->m_iStartRow < iEventRow )
		{
			iEventRow = itWS->m_iStartRow;
			iEventType = FOUND_WARP;
		}
		if( itBPMS != m_BPMSegments.end() && itBPMS->m_iStartRow < iEventRow )
		{
			iEventRow = itBPMS->m_iStartRow;
			iEventType = FOUND_BPM_CHANGE;
		}
		if( itSS != m_StopSegments.end() && itSS->m_bDelay && itSS->m_iStartRow < iEventRow )
		{
			iEventRow = itSS->m_iStartRow;
			iEventType = FOUND_STOP;
		}
		if( BeatToNoteRow(fBeat) < iEventRow )
		{
			iEventRow = BeatToNoteRow(fBeat);
			iEventType = FOUND_MARKER;
		}
		if( itSS != m_StopSegments.end() && !itSS->m_bDelay && itSS->m_iStartRow < iEventRow )
		{
			iEventRow = itSS->m_iStartRow;
			iEventType = FOUND_STOP;
		}
		float fTimeToNextEvent = bIsWarping ? 0 : NoteRowToBeat( iEventRow - iLastRow ) / fBPS;
		float fNextEventTime   = fLastTime + fTimeToNextEvent;
		fLastTime = fNextEventTime;
		switch( iEventType )
		{
		case FOUND_WARP_DESTINATION:
			bIsWarping = false;
			break;
		case FOUND_WARP:
			bIsWarping = true;
			if( itWS->m_fEndBeat > fWarpDestination )
			{
				fWarpDestination = itWS->m_fEndBeat;
			}
			itWS ++;
			break;
		case FOUND_BPM_CHANGE:
			fBPS = itBPMS->m_fBPS;
			itBPMS ++;
			break;
		case FOUND_STOP:
			fTimeToNextEvent = bIsWarping ? 0 : itSS->m_fStopSeconds;
			fNextEventTime   = fLastTime + fTimeToNextEvent;
			fLastTime = fNextEventTime;
			itSS ++;
			break;
		case FOUND_MARKER:
			return fLastTime;	
		}
		iLastRow = iEventRow;
	}
	
	// won't reach here, unless BeatToNoteRow(fBeat > INT_MAX) (impossible)
	
}