log contents:
01:39.560: return part 1: 374
01:39.560: return part 2: 249
01:39.560: return in full: -1828379652
01:39.560: marv pct = -1610612736 and marv count = 1073219641
01:39.560: return part 1: 96
01:39.560: return part 2: 249
01:39.560: return in full: 258732970
01:39.560: perf pct = 0 and perf count = 1071164601
01:39.560: return part 1: 28
01:39.560: return part 2: 249
01:39.560: return in full: -1845628517
01:39.560: great pct = -1610612736 and great count = 1069336962
01:39.560: return part 1: 0
01:39.560: return part 2: 249
01:39.560: return in full: 0
01:39.560: good pct = 0 and good count = 0
01:39.560: return part 1: 0
01:39.560: return part 2: 249
01:39.560: return in full: 0
01:39.560: boo pct = 0 and boo count = 0
01:39.560: return part 1: 0
01:39.560: return part 2: 249
01:39.560: return in full: 0
01:39.561: miss pct = 0 and miss count = 0

Then the code:
float StageStats::GetTapPercentages( PlayerNumber pn, TapNoteScore tns ) const
{
	int iTotalTaps = 0;
	for( int i=TNS_MISS; i<NUM_TAP_NOTE_SCORES; i++ )
	{
		iTotalTaps += iTapNoteScores[pn][i];
	}
	LOG->Trace( "return part 1: %i", ( PREFSMAN->m_iGradeWeightMarvelous * iTapNoteScores[pn][tns] ) );
	LOG->Trace( "return part 2: %i", iTotalTaps );
	int iTaps = ( PREFSMAN->m_iGradeWeightMarvelous * iTapNoteScores[pn][tns] );
	float fTapPercentage = (float)iTaps / (float)iTotalTaps;
	LOG->Trace( "return in full: %i", fTapPercentage );
	return fTapPercentage;
}