Improve rng algorithm. (#56)

Author: Alinshans

src/MineCase.Algorithm/UniformRNG.cs

@@ -12,9 +12,11 @@ public struct UniformRNG
         private static readonly ulong _increment = 1442695040888963407;
 
         private ulong _state;
+        private uint _count;
 
         public UniformRNG(ulong state)
         {
+            _count = 101;
             if (state == 0)
             {
                 var time = DateTime.Now;
@@ -97,10 +99,21 @@ public double Uniform(double a, double b)
 
         private uint Next()
         {
-            _state ^= _state >> 13;
-            _state ^= (_state << 7) | 0x9d2c5680;
-            _state ^= (_state << 15) & 0xefc67a5b;
-            _state = _state * _multiplier + _increment;
+            --_count;
+            if (_count == 0)
+            {
+                for (int i = 0; i < 4; ++i)
+                {
+                    _state = _state * _multiplier + _increment;
+                }
+
+                _count = 101;
+            }
+
+            _state ^= _state >> 21;
+            _state ^= (_state << 13) | 0x73a4b9de9d2c5680;
+            _state ^= (_state << 29) & 0x5b3e6da7efc67a5b;
+            _state ^= _state >> 33;
             return (uint)_state;
         }
     }

tests/UnitTest/RNGTest.cs

@@ -6,6 +6,7 @@
 using ImageSharp;
 using MineCase.Algorithm;
 using Xunit;
+using System.Diagnostics;
 
 namespace MineCase.UnitTest
 {
@@ -79,7 +80,7 @@ public void TestFrequencyImg()
         }
 
         [Fact]
-        public void TesIntNoiseImg()
+        public void TestIntNoiseImg()
         {
             var rng = new UniformRNG(0);
 
@@ -103,7 +104,7 @@ public void TesIntNoiseImg()
         }
 
         [Fact]
-        public void TesFloatNoiseImg()
+        public void TestFloatNoiseImg()
         {
             var rng = new UniformRNG(0);
 
@@ -127,7 +128,7 @@ public void TesFloatNoiseImg()
         }
 
         [Fact]
-        public void TesDoubleNoiseImg()
+        public void TestDoubleNoiseImg()
         {
             var rng = new UniformRNG(0);
 
@@ -149,5 +150,35 @@ public void TesDoubleNoiseImg()
                 image.SaveAsBmp(file);
             }
         }
+
+        [Fact]
+        public void TestRNGPerformance()
+        {
+            var rng = new UniformRNG(0);
+            var random = new Random();
+            Stopwatch sw = new Stopwatch();
+
+            sw.Start();
+            int res = 0;
+            for (int i = 0; i < 10000000; ++i)
+            {
+                res += rng.NextInt32();
+            }
+
+            sw.Stop();
+            var t1 = sw.ElapsedMilliseconds;
+
+            sw.Start();
+            res = 0;
+            for (int i = 0; i < 10000000; ++i)
+            {
+                res += random.Next();
+            }
+
+            sw.Stop();
+            var t2 = sw.ElapsedMilliseconds;
+
+            Assert.True(t1 < t2);
+        }
     }
 }