Fix LADSPA hint calculation for logarithmic parameters

For parameters from 1 to 65535 with defaults of 4096 and 128, the old
logic picked “low” and “low”, resulting in default values of 16 for
both, whereas this new logic picks “high” and “middle”, resulting in
defaults of 4096 and 256.

distrho/src/DistrhoPluginLADSPA+DSSI.cpp

@@ -16,6 +16,8 @@
 
 #include "DistrhoPluginInternal.hpp"
 
+#include <cmath>
+
 #if DISTRHO_PLUGIN_WANT_PARAMETER_VALUE_CHANGE_REQUEST
 # error Cannot use parameter value change request with LADSPA or DSSI
 #endif
@@ -646,9 +648,21 @@ static const struct DescriptorInitializer
                     portRangeHints[port].HintDescriptor |= LADSPA_HINT_DEFAULT_MAXIMUM;
                 else
                 {
-                    const float middleValue =  ranges.min/2.0f + ranges.max/2.0f;
-                    const float middleLow   = (ranges.min/2.0f + middleValue/2.0f)/2.0f + middleValue/2.0f;
-                    const float middleHigh  = (ranges.max/2.0f + middleValue/2.0f)/2.0f + middleValue/2.0f;
+                    float middleValue;
+                    float middleLow;
+                    float middleHigh;
+                    if (hints & kParameterIsLogarithmic)
+                    {
+                        middleValue = std::sqrt(ranges.min * ranges.max);
+                        middleLow   = std::sqrt(std::sqrt(ranges.min * middleValue) * middleValue);
+                        middleHigh  = std::sqrt(std::sqrt(ranges.max * middleValue) * middleValue);
+                    }
+                    else
+                    {
+                        middleValue =  ranges.min/2.0f + ranges.max/2.0f;
+                        middleLow   = (ranges.min/2.0f + middleValue/2.0f)/2.0f + middleValue/2.0f;
+                        middleHigh  = (ranges.max/2.0f + middleValue/2.0f)/2.0f + middleValue/2.0f;
+                    }
 
                     /**/ if (defValue < middleLow)
                         portRangeHints[port].HintDescriptor |= LADSPA_HINT_DEFAULT_LOW;