Fix for issue #3816 - FM or heavy PM in TripleOscillator makes output…

include/Oscillator.h

@@ -97,7 +97,7 @@ class LMMS_EXPORT Oscillator
 
 	static inline sample_t triangleSample( const float _sample )
 	{
-		const float ph = fraction( _sample );
+		const float ph = absFraction( _sample );
 		if( ph <= 0.25f )
 		{
 			return ph * 4.0f;
@@ -111,17 +111,17 @@ class LMMS_EXPORT Oscillator
 
 	static inline sample_t sawSample( const float _sample )
 	{
-		return -1.0f + fraction( _sample ) * 2.0f;
+		return -1.0f + absFraction( _sample ) * 2.0f;
 	}
 
 	static inline sample_t squareSample( const float _sample )
 	{
-		return ( fraction( _sample ) > 0.5f ) ? -1.0f : 1.0f;
+		return ( absFraction( _sample ) > 0.5f ) ? -1.0f : 1.0f;
 	}
 
 	static inline sample_t moogSawSample( const float _sample )
 	{
-		const float ph = fraction( _sample );
+		const float ph = absFraction( _sample );
 		if( ph < 0.5f )
 		{
 			return -1.0f + ph * 4.0f;
@@ -131,7 +131,7 @@ class LMMS_EXPORT Oscillator
 
 	static inline sample_t expSample( const float _sample )
 	{
-		float ph = fraction( _sample );
+		float ph = absFraction( _sample );
 		if( ph > 0.5f )
 		{
 			ph = 1.0f - ph;

include/lmms_math.h

@@ -42,22 +42,41 @@ using namespace std;
 
 static inline float absFraction( const float _x )
 {
-	return( _x - ( _x >= 0.0f ? floorf( _x ) : floorf( _x ) - 1 ) );
+	return( _x - floorf( _x ) );
 }
 
 static inline float fraction( const float _x )
 {
-	return( _x - floorf( _x ) );
+	return( _x - floorf( _x ) - ( _x >= 0.0f ? 0.0 : 1.0 ) );
 }
 
 #else
 
+/*!
+ * @brief Returns the wrapped fractional part of a float, a value between 0.0f and 1.0f.
+ *
+ * absFraction( 2.3) =>  0.3
+ * absFraction(-2.3) =>  0.7
+ *
+ * Note that this not the same as the absolute value of the fraction (as the function name suggests).
+ * If the result is interpreted as a phase of an oscillator, it makes that negative phases are
+ * converted to positive phases.
+ */
 static inline float absFraction( const float _x )
 {
 	return( _x - ( _x >= 0.0f ? static_cast<int>( _x ) :
 						static_cast<int>( _x ) - 1 ) );
 }
 
+/*!
+ * @brief Returns the fractional part of a float, a value between -1.0f and 1.0f.
+ *
+ * fraction( 2.3) =>  0.3
+ * fraction(-2.3) => -0.3
+ *
+ * Note that if the return value is used as a phase of an oscillator, that the oscillator must support
+ * negative phases.
+ */
 static inline float fraction( const float _x )
 {
 	return( _x - static_cast<int>( _x ) );

src/core/Oscillator.cpp

@@ -316,8 +316,7 @@ inline void Oscillator::recalcPhase()
 		m_phaseOffset = m_ext_phaseOffset;
 		m_phase += m_phaseOffset;
 	}
-	m_phase = absFraction( m_phase )+2;	// make sure we're not running
-						// negative when doing PM
+	m_phase = absFraction( m_phase );
 }