From 2c82c70f970471c402e1d87f164ea58af4972dea Mon Sep 17 00:00:00 2001
From: Thorsten Sommer <mail@tsommer.org>
Date: Wed, 23 Sep 2020 21:10:55 +0200
Subject: [PATCH] First implementation

---
 FastRng/MultiThreadedRng.cs | 113 ++++++++++++++++++++++++++++++++++++
 1 file changed, 113 insertions(+)
 create mode 100644 FastRng/MultiThreadedRng.cs

diff --git a/FastRng/MultiThreadedRng.cs b/FastRng/MultiThreadedRng.cs
new file mode 100644
index 0000000..ca588e8
--- /dev/null
+++ b/FastRng/MultiThreadedRng.cs
@@ -0,0 +1,113 @@
+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.Runtime.CompilerServices;
+using System.Threading;
+using System.Threading.Channels;
+using System.Threading.Tasks;
+
+namespace FastRng
+{
+    public sealed class MultiThreadedRng : IRandom
+    {
+        #if DEBUG
+            private const int CAPACITY_RANDOM_NUMBERS_4_SOURCE = 10_000;
+        #else
+            private const int CAPACITY_RANDOM_NUMBERS_4_SOURCE = 16_000_000;
+        #endif
+        
+        private readonly System.Random rng = new System.Random();
+        private readonly CancellationTokenSource producerToken = new CancellationTokenSource();
+        
+        private readonly Thread producerRandom1;
+        private readonly Thread producerRandom2;
+
+        private readonly Channel<double> channelRandom = Channel.CreateBounded<double>(new BoundedChannelOptions(CAPACITY_RANDOM_NUMBERS_4_SOURCE)
+        {
+            FullMode = BoundedChannelFullMode.Wait,
+            SingleReader = false,
+            SingleWriter = false,
+        });
+
+        #region Constructors
+
+        public MultiThreadedRng()
+        {
+            this.producerRandom1 = new Thread(() => MultiThreadedRng.RandomProducer(this.rng, this.channelRandom.Writer, this.producerToken.Token)) {IsBackground = true};
+            this.producerRandom2 = new Thread(() => MultiThreadedRng.RandomProducer(this.rng, this.channelRandom.Writer, this.producerToken.Token)) {IsBackground = true};
+            this.producerRandom1.Start();
+            this.producerRandom2.Start();
+        }
+
+        public MultiThreadedRng(int seed)
+        {
+            this.rng = new Random(seed);
+            
+            this.producerRandom1 = new Thread(() => MultiThreadedRng.RandomProducer(this.rng, this.channelRandom.Writer, this.producerToken.Token)) {IsBackground = true};
+            this.producerRandom2 = new Thread(() => MultiThreadedRng.RandomProducer(this.rng, this.channelRandom.Writer, this.producerToken.Token)) {IsBackground = true};
+            
+            this.producerRandom1.Start();
+            this.producerRandom2.Start();
+        }
+
+        #endregion
+        
+        [ExcludeFromCodeCoverage]
+        private static async void RandomProducer(System.Random random, ChannelWriter<double> channelWriter, CancellationToken cancellationToken)
+        {
+            while (!cancellationToken.IsCancellationRequested)
+            {
+                //
+                // We using double as basis for anything. That's what .NET does internally as well, cf. https://github.com/dotnet/runtime/blob/6072e4d3a7a2a1493f514cdf4be75a3d56580e84/src/libraries/System.Private.CoreLib/src/System/Random.cs.
+                // random.NextDouble() returns Sample(). Next(min, max) uses GetSampleForLargeRange().
+                // Thus, we re-implement GetSampleForLargeRange() and use its numbers as source for everything. 
+                //
+                
+                var buffer = new double[CAPACITY_RANDOM_NUMBERS_4_SOURCE];
+                for (var n = 0; n < buffer.Length && !cancellationToken.IsCancellationRequested; n++)
+                {
+                    #region Re-implementation of GetSampleForLargeRange() method of .NET
+
+                    var result = random.Next(); // Notice: random.Next() is identical to InternalSample()
+                    var negative = random.Next() % 2 == 0; // Notice: random.Next() is identical to InternalSample()
+                    if (negative)
+                        result = -result;
+                    
+                    double d = result;
+                    d += (int.MaxValue - 1); // get a number in range [0 .. 2 * Int32MaxValue - 1)
+                    d /= 2 * (uint)int.MaxValue - 1;
+
+                    #endregion
+                    
+                    buffer[n] = d;
+                }
+
+                for (var n = 0; n < buffer.Length && !cancellationToken.IsCancellationRequested; n++) 
+                    await channelWriter.WriteAsync(buffer[n], cancellationToken);
+            }
+        }
+
+        #region Implementing interface
+
+        public async Task<uint> NextNumber(uint rangeStart, uint rangeEnd, CancellationToken cancel = default(CancellationToken))
+        {
+            var range = rangeEnd - rangeStart;
+            return (uint) ((await this.channelRandom.Reader.ReadAsync(cancel) * range) + rangeStart);
+        }
+
+        public async Task<ulong> NextNumber(ulong rangeStart, ulong rangeEnd, CancellationToken cancel = default(CancellationToken))
+        {
+            var range = rangeEnd - rangeStart;
+            return (ulong) ((await this.channelRandom.Reader.ReadAsync(cancel) * range) + rangeStart);
+        }
+
+        public async Task<float> NextNumber(float rangeStart, float rangeEnd, CancellationToken cancel = default(CancellationToken))
+        {
+            var range = rangeEnd - rangeStart;
+            return (float) ((await this.channelRandom.Reader.ReadAsync(cancel) * range) + rangeStart);
+        }
+
+        public void StopProducer() => this.producerToken.Cancel();
+
+        #endregion
+    }
+}
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