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+/*
+ * Copyright 2009 Phil Burk, Mobileer Inc
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.jsyn.unitgen;
+
+import com.jsyn.ports.UnitInputPort;
+import com.jsyn.ports.UnitVariablePort;
+
+/**
+ * Output approaches Input exponentially. This unit provides a slowly changing value that approaches
+ * its Input value exponentially. The equation is:
+ * 
+ * <PRE>
+ * Output = Output + Rate * (Input - Output);
+ * </PRE>
+ * 
+ * Note that the output may never reach the value of the input. It approaches the input
+ * asymptotically. The Rate is calculated internally based on the value on the halfLife port. Rate
+ * is generally just slightly less than 1.0.
+ * 
+ * @author Phil Burk (C) 2009 Mobileer Inc
+ * @version 016
+ * @see LinearRamp
+ * @see ExponentialRamp
+ * @see ContinuousRamp
+ */
+public class AsymptoticRamp extends UnitFilter {
+    public UnitVariablePort current;
+    public UnitInputPort halfLife;
+    private double previousHalfLife = -1.0;
+    private double decayScalar = 0.99;
+
+    /* Define Unit Ports used by connect() and set(). */
+    public AsymptoticRamp() {
+        addPort(halfLife = new UnitInputPort(1, "HalfLife", 0.1));
+        addPort(current = new UnitVariablePort("Current"));
+    }
+
+    @Override
+    public void generate(int start, int limit) {
+        double[] outputs = output.getValues();
+        double[] inputs = input.getValues();
+        double currentHalfLife = halfLife.getValues()[0];
+        double currentValue = current.getValue();
+        double inputValue = currentValue;
+
+        if (currentHalfLife != previousHalfLife) {
+            decayScalar = this.convertHalfLifeToMultiplier(currentHalfLife);
+            previousHalfLife = currentHalfLife;
+        }
+
+        for (int i = start; i < limit; i++) {
+            inputValue = inputs[i];
+            currentValue = currentValue + decayScalar * (inputValue - currentValue);
+            outputs[i] = currentValue;
+        }
+
+        /*
+         * When current gets close to input, set current to input to prevent FP underflow, which can
+         * cause a severe performance degradation in 'C'.
+         */
+        if (Math.abs(inputValue - currentValue) < VERY_SMALL_FLOAT) {
+            currentValue = inputValue;
+        }
+
+        current.setValue(currentValue);
+    }
+}