From f7042977a99910fa9c2f79ed64c90a1e428e42f5 Mon Sep 17 00:00:00 2001
From: Vesa <contact.diizy@nbl.fi>
Date: Sat, 21 Jun 2014 10:56:28 +0300
Subject: [PATCH] Logscale: Fix negative ranges This fixes errors that happen
 on models that have both logarithmic scale and a range that goes to the
 negative.

---
 include/lmms_math.h      | 16 ++++++++++++++--
 src/gui/widgets/knob.cpp |  6 ++++--
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/include/lmms_math.h b/include/lmms_math.h
index 9c22014af..6f361c971 100644
--- a/include/lmms_math.h
+++ b/include/lmms_math.h
@@ -128,13 +128,24 @@ static inline double sinc( double _x )
 }
 
 
+//! @brief Exponential function that deals with negative bases
+static inline float signedPowf( float v, float e )
+{
+	return v < 0 
+		? powf( -v, e ) * -1.0f
+		: powf( v, e );
+}
+
+
 //! @brief Scales @value from linear to logarithmic.
 //! Value should be within [0,1]
 static inline float logToLinearScale( float min, float max, float value )
 {
 	if( min < 0 )
 	{
-		return powf( value * ( 1.0f - min / max ) + min / max, F_E ) * ( max - min ) + min;
+		const float mmax = qMax( qAbs( min ), qAbs( max ) );
+		const float val = value * ( max - min ) + min;
+		return signedPowf( val / mmax, F_E ) * mmax;
 	}
 	return powf( value, F_E ) * ( max - min ) + min;
 }
@@ -147,7 +158,8 @@ static inline float linearToLogScale( float min, float max, float value )
 	const float val = ( value - min ) / ( max - min );
 	if( min < 0 )
 	{
-		return powf( val * ( 1.0f - min / max ) + min / max, EXP ) * ( max - min ) + min;
+		const float mmax = qMax( qAbs( min ), qAbs( max ) );
+		return signedPowf( value / mmax, EXP ) * mmax;
 	}
 	return powf( val, EXP ) * ( max - min ) + min;
 }
diff --git a/src/gui/widgets/knob.cpp b/src/gui/widgets/knob.cpp
index 3d127d4d2..7bb226795 100644
--- a/src/gui/widgets/knob.cpp
+++ b/src/gui/widgets/knob.cpp
@@ -674,8 +674,10 @@ void knob::setPosition( const QPoint & _p )
 
 	if( model()->isScaleLogarithmic() ) // logarithmic code
 	{
-		const float pos = ( oldValue - model()->minValue() ) / model()->range();
-		const float ratio = 0.1f + pos * 15.f;
+		const float pos = model()->minValue() < 0 
+			? oldValue / qMax( qAbs( model()->maxValue() ), qAbs( model()->minValue() ) )
+			: ( oldValue - model()->minValue() ) / model()->range();
+		const float ratio = 0.1f + qAbs( pos ) * 15.f;
 		float newValue = value * ratio;
 		if( qAbs( newValue ) >= step )
 		{