Restore backwards compatibility of Environment and remove unused default instance of PCG

Author: abeham

SimSharp/Core/Environment.cs

@@ -21,34 +21,6 @@ You should have received a copy of the GNU General Public License
 using System.IO;
 
 namespace SimSharp {
-
-  /// <summary>
-  /// Environments hold the event queues, schedule and process events.
-  /// </summary>
-  [Obsolete("Use class Simulation or ThreadSafeSimulation instead. Due to name clashes with System.Environment the class SimSharp.Environment is being outphased.")]
-  public class Environment : ThreadSafeSimulation {
-    public Environment()
-      : base() {
-      Random = new SystemRandom();
-    }
-    public Environment(TimeSpan? defaultStep)
-      : base(defaultStep) {
-      Random = new SystemRandom();
-    }
-    public Environment(int randomSeed, TimeSpan? defaultStep = null)
-      : base(randomSeed, defaultStep) {
-      Random = new SystemRandom(randomSeed);
-    }
-    public Environment(DateTime initialDateTime, TimeSpan? defaultStep = null)
-      : base(initialDateTime, defaultStep) {
-      Random = new SystemRandom();
-    }
-    public Environment(DateTime initialDateTime, int randomSeed, TimeSpan? defaultStep = null)
-      : base(initialDateTime, randomSeed, defaultStep) {
-      Random = new SystemRandom(randomSeed);
-    }
-  }
-
   /// <summary>
   /// Simulation hold the event queues, schedule and process events.
   /// </summary>
@@ -410,7 +382,7 @@ public TimeSpan RandExponential(TimeSpan mean) {
     /// <param name="mu">The mean of the normal distribution.</param>
     /// <param name="sigma">The standard deviation of the normal distribution.</param>
     /// <returns>A number that is normal distributed.</returns>
-    public double RandNormal(IRandom random, double mu, double sigma) {
+    public virtual double RandNormal(IRandom random, double mu, double sigma) {
       if (useSpareNormal) {
         useSpareNormal = false;
         return spareNormal * sigma + mu;
@@ -874,4 +846,43 @@ public override DateTime Peek() {
       }
     }
   }
+
+  /// <summary>
+  /// Environments hold the event queues, schedule and process events.
+  /// </summary>
+  [Obsolete("Use class Simulation or ThreadSafeSimulation instead. Due to name clashes with System.Environment the class SimSharp.Environment is being outphased.")]
+  public class Environment : ThreadSafeSimulation {
+    public Environment()
+      : base() {
+      Random = new SystemRandom();
+    }
+    public Environment(TimeSpan? defaultStep)
+      : base(defaultStep) {
+      Random = new SystemRandom();
+    }
+    public Environment(int randomSeed, TimeSpan? defaultStep = null)
+      : base(randomSeed, defaultStep) {
+      Random = new SystemRandom(randomSeed);
+    }
+    public Environment(DateTime initialDateTime, TimeSpan? defaultStep = null)
+      : base(initialDateTime, defaultStep) {
+      Random = new SystemRandom();
+    }
+    public Environment(DateTime initialDateTime, int randomSeed, TimeSpan? defaultStep = null)
+      : base(initialDateTime, randomSeed, defaultStep) {
+      Random = new SystemRandom(randomSeed);
+    }
+
+    protected static readonly double NormalMagicConst = 4 * Math.Exp(-0.5) / Math.Sqrt(2.0);
+    public override double RandNormal(IRandom random, double mu, double sigma) {
+      double z, zz, u1, u2;
+      do {
+        u1 = random.NextDouble();
+        u2 = 1 - random.NextDouble();
+        z = NormalMagicConst * (u1 - 0.5) / u2;
+        zz = z * z / 4.0;
+      } while (zz > -Math.Log(u2));
+      return mu + z * sigma;
+    }
+  }
 }

SimSharp/Random/Pcg.cs

@@ -69,19 +69,7 @@ internal class Pcg {
     ulong _increment = 1442695040888963407ul;
     const ulong Multiplier = 6364136223846793005ul;
     const double ToDouble01 = 1.0 / 4294967296.0;
-
-    // This attribute ensures that every thread will get its own instance of PCG.
-    // An alternative, since PCG supports streams, is to use a different stream per
-    // thread. 
-    [ThreadStatic]
-    static Pcg _defaultInstance;
-    /// <summary>
-    /// Default instance.
-    /// </summary>
-    public static Pcg Default {
-      get { return _defaultInstance ?? (_defaultInstance = new Pcg(PcgSeed.GuidBasedSeed())); }
-    }
-
+    
     public int Next() {
       uint result = NextUInt();
       return (int)(result >> 1);

Tests/EnvironmentTests.cs

@@ -162,5 +162,18 @@ private IEnumerable<Event> ReproducibleProcess(Simulation env) {
       yield return env.TimeoutD(t3);
       env.ActiveProcess.Succeed(t1 + t2 + t3);
     }
+
+    [Fact]
+    public void EnvironmentBackwardsCompat() {
+      // make sure it returns the same normal-distributed random numbers as the 3.0.11 Environment
+#pragma warning disable CS0618 // Type or member is obsolete
+      var env = new Environment(randomSeed: 10);
+#pragma warning restore CS0618 // Type or member is obsolete
+      var rndNumbers = Enumerable.Range(0, 10).Select(x => env.RandNormal(0, 1)).ToArray();
+      var old = new[] { 1.439249790053017, 0.539700657754765, -0.35962836744484883,
+0.37645276686883905, 0.037506631053281031, -0.92536789644140882, -0.87027850838312693,
+0.65864875161591829, 0.46713487767696055, -0.37878389025311837};
+      Assert.Equal(old, rndNumbers);
+    }
   }
 }