Initial commit of code.

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diff --git a/src/com/jsyn/unitgen/ExponentialRamp.java b/src/com/jsyn/unitgen/ExponentialRamp.java
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+/*
+ * Copyright 2010 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 and will reach it in the specified time.
+ * 
+ * @author Phil Burk (C) 2010 Mobileer Inc
+ * @version 016
+ * @see LinearRamp
+ * @see AsymptoticRamp
+ * @see ContinuousRamp
+ */
+public class ExponentialRamp extends UnitFilter {
+    public UnitInputPort time;
+    public UnitVariablePort current;
+
+    private double target;
+    private double timeHeld = 0.0;
+    private double scaler = 1.0;
+
+    public ExponentialRamp() {
+        addPort(time = new UnitInputPort("Time"));
+        addPort(current = new UnitVariablePort("Current", 1.0));
+    }
+
+    @Override
+    public void generate(int start, int limit) {
+        double[] outputs = output.getValues();
+        double currentInput = input.getValues()[0];
+        double currentTime = time.getValues()[0];
+        double currentValue = current.getValue();
+
+        if (currentTime != timeHeld) {
+            scaler = convertTimeToExponentialScaler(currentTime, currentValue, currentInput);
+            timeHeld = currentTime;
+        }
+
+        // If input has changed, start new segment.
+        // Equality check is OK because we set them exactly equal below.
+        if (currentInput != target) {
+            scaler = convertTimeToExponentialScaler(currentTime, currentValue, currentInput);
+            target = currentInput;
+        }
+
+        if (currentValue < target) {
+            // Going up.
+            for (int i = start; i < limit; i++) {
+                currentValue = currentValue * scaler;
+                if (currentValue > target) {
+                    currentValue = target;
+                    scaler = 1.0;
+                }
+                outputs[i] = currentValue;
+            }
+        } else if (currentValue > target) {
+            // Going down.
+            for (int i = start; i < limit; i++) {
+                currentValue = currentValue * scaler;
+                if (currentValue < target) {
+                    currentValue = target;
+                    scaler = 1.0;
+                }
+                outputs[i] = currentValue;
+            }
+
+        } else if (currentValue == target) {
+            for (int i = start; i < limit; i++) {
+                outputs[i] = target;
+            }
+        }
+
+        current.setValue(currentValue);
+    }
+
+    private double convertTimeToExponentialScaler(double duration, double source, double target) {
+        double product = source * target;
+        if (product <= 0.0000001) {
+            throw new IllegalArgumentException(
+                    "Exponential ramp crosses zero or gets too close to zero.");
+        }
+        // Calculate scaler so that scaler^frames = target/source
+        double numFrames = duration * getFrameRate();
+        return Math.pow((target / source), (1.0 / numFrames));
+    }
+}