support for .NET framework 3.5

Still have bugs

Net35/HandyControl_Net35/Expression/Drawing/RandomEngine.cs

@@ -0,0 +1,45 @@
+using System;
+
+namespace HandyControl.Expression.Drawing
+{
+    internal class RandomEngine
+    {
+        private double? _anotherSample;
+
+        private Random _random;
+
+        public RandomEngine(long seed) => Initialize(seed);
+
+        private double Gaussian()
+        {
+            double num;
+            double num2;
+            double num3;
+            if (_anotherSample.HasValue)
+            {
+                var num4 = _anotherSample.Value;
+                _anotherSample = null;
+                return num4;
+            }
+
+            do
+            {
+                num2 = 2.0 * Uniform() - 1.0;
+                num3 = 2.0 * Uniform() - 1.0;
+                num = num2 * num2 + num3 * num3;
+            } while (num >= 1.0);
+
+            var num5 = Math.Sqrt(-2.0 * Math.Log(num) / num);
+            _anotherSample = num2 * num5;
+            return num3 * num5;
+        }
+
+        private void Initialize(long seed) => _random = new Random((int) seed);
+
+        public double NextGaussian(double mean, double variance) => Gaussian() * variance + mean;
+
+        public double NextUniform(double min, double max) => Uniform() * (max - min) + min;
+
+        private double Uniform() => _random.NextDouble();
+    }
+}