From 74470f90bac33910fb25340eb71c993d0af552a7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E5=9F=83=E5=8D=9A=E6=8B=89=E9=85=B1?= <vhtmfu@outlook.com>
Date: Fri, 7 Jan 2022 14:27:40 +0800
Subject: [PATCH] RandomExtensions.NextBigIntegerSequence

---
 .../Random/RandomExtensionTests.cs            | 18 +++++++++++
 src/Numerics/Random/RandomExtensions.cs       | 32 ++++++++++++++++++-
 2 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/src/Numerics.Tests/Random/RandomExtensionTests.cs b/src/Numerics.Tests/Random/RandomExtensionTests.cs
index 99c732c2..5bb84713 100644
--- a/src/Numerics.Tests/Random/RandomExtensionTests.cs
+++ b/src/Numerics.Tests/Random/RandomExtensionTests.cs
@@ -29,6 +29,8 @@
 
 using MathNet.Numerics.Random;
 using NUnit.Framework;
+using System.Numerics;
+using System.Collections.Generic;
 
 namespace MathNet.Numerics.UnitTests.Random
 {
@@ -48,6 +50,22 @@ namespace MathNet.Numerics.UnitTests.Random
             rnd.NextInt64();
         }
 
+        /// <summary>
+        /// Can sample BigInteger
+        /// </summary>
+        [Test]
+        public void CanSampleBigInteger()
+        {
+            var rnd = new System.Random(0);
+            IEnumerator<BigInteger> Sequence = rnd.NextBigIntegerSequence((BigInteger)long.MinValue * 3, (BigInteger)long.MaxValue * 3).GetEnumerator();
+            Sequence.MoveNext();
+            System.Console.WriteLine(Sequence.Current);
+            Sequence.MoveNext();
+            System.Console.WriteLine(Sequence.Current);
+            Sequence.MoveNext();
+            System.Console.WriteLine(Sequence.Current);
+        }
+
         /// <summary>
         /// Can sample full range int32.
         /// </summary>
diff --git a/src/Numerics/Random/RandomExtensions.cs b/src/Numerics/Random/RandomExtensions.cs
index c351e3d8..0ba53982 100644
--- a/src/Numerics/Random/RandomExtensions.cs
+++ b/src/Numerics/Random/RandomExtensions.cs
@@ -29,6 +29,8 @@
 
 using System;
 using System.Collections.Generic;
+using System.Numerics;
+using System.Linq;
 
 namespace MathNet.Numerics.Random
 {
@@ -167,7 +169,7 @@ namespace MathNet.Numerics.Random
         }
 
         /// <summary>
-        /// Returns an infinite sequence of uniform random numbers greater than or equal to 0.0 and less than 1.0.
+        /// Returns an infinite sequence of uniform random 32-bit signed integers within the specified range.
         /// </summary>
         /// <remarks>
         /// This extension is thread-safe if and only if called on an random number
@@ -191,6 +193,34 @@ namespace MathNet.Numerics.Random
             }
         }
 
+        /// <summary>
+        /// Returns an infinite sequence of uniform random <see cref="System.Numerics.BigInteger"/> within the specified range.
+        /// </summary>
+        /// <remarks>
+        /// This extension is thread-safe if and only if called on an random number
+        /// generator provided by Math.NET Numerics or derived from the RandomSource class.
+        /// </remarks>
+        public static IEnumerable<BigInteger> NextBigIntegerSequence(this System.Random rnd, BigInteger minInclusive, BigInteger maxExclusive)
+        {
+            BigInteger AbsoluteRange = maxExclusive - minInclusive;
+            int NumBytes = (int)Math.Ceiling(BigInteger.Log(AbsoluteRange, byte.MaxValue) * 2);
+            byte[] ByteSequence = Enumerable.Repeat(byte.MaxValue, NumBytes + 1).ToArray();
+            ByteSequence[NumBytes] = 0;
+            BigInteger RandomNumber = new BigInteger(ByteSequence);
+            BigInteger ValidRange = RandomNumber - RandomNumber % AbsoluteRange;
+            while(true)
+            {
+                do
+                {
+                    rnd.NextBytes(ByteSequence);
+                    ByteSequence[NumBytes] = 0;
+                    RandomNumber = new BigInteger(ByteSequence);
+                }
+                while (RandomNumber >= ValidRange);
+                yield return RandomNumber % AbsoluteRange + minInclusive;
+            }
+        }
+
         /// <summary>
         /// Returns a nonnegative random number less than <see cref="Int64.MaxValue"/>.
         /// </summary>