From 484f1e44f2bdf2661505177a53e8489a565125b6 Mon Sep 17 00:00:00 2001
From: Christoph Ruegg <git@cdrnet.ch>
Date: Thu, 18 Aug 2016 14:20:48 +0200
Subject: [PATCH] Random: improved fallbacks on zero-minInclusive integer
 sampling

---
 src/Numerics/Random/CryptoRandomSource.cs |  2 +-
 src/Numerics/Random/RandomSource.cs       | 86 +++++++++++++++++++----
 src/Numerics/Random/SystemRandomSource.cs |  5 ++
 3 files changed, 78 insertions(+), 15 deletions(-)

diff --git a/src/Numerics/Random/CryptoRandomSource.cs b/src/Numerics/Random/CryptoRandomSource.cs
index 0f068ac8..c25e3b8f 100644
--- a/src/Numerics/Random/CryptoRandomSource.cs
+++ b/src/Numerics/Random/CryptoRandomSource.cs
@@ -110,7 +110,7 @@ namespace MathNet.Numerics.Random
             var bytes = new byte[4];
             _crypto.GetBytes(bytes);
             uint uint32 = BitConverter.ToUInt32(bytes, 0);
-            int int31 = (int)uint32 >> 1;
+            int int31 = (int)(uint32 >> 1);
             if (int31 == int.MaxValue)
             {
                 return DoSampleInteger();
diff --git a/src/Numerics/Random/RandomSource.cs b/src/Numerics/Random/RandomSource.cs
index a1648748..b0002ddb 100644
--- a/src/Numerics/Random/RandomSource.cs
+++ b/src/Numerics/Random/RandomSource.cs
@@ -159,11 +159,11 @@ namespace MathNet.Numerics.Random
             {
                 lock (_lock)
                 {
-                    return DoSampleInteger(0, maxExclusive);
+                    return DoSampleInteger(maxExclusive);
                 }
             }
 
-            return DoSampleInteger(0, maxExclusive);
+            return DoSampleInteger(maxExclusive);
         }
 
         /// <summary>
@@ -182,9 +182,14 @@ namespace MathNet.Numerics.Random
                 throw new ArgumentException(Resources.ArgumentMinValueGreaterThanMaxValue);
             }
 
-            if (maxExclusive == int.MaxValue && minInclusive == 0)
+            if (minInclusive == 0)
             {
-                return Next();
+                if (maxExclusive == int.MaxValue)
+                {
+                    return Next();
+                }
+
+                return Next(maxExclusive);
             }
 
             if (_threadSafe)
@@ -234,6 +239,38 @@ namespace MathNet.Numerics.Random
             return values;
         }
 
+        /// <summary>
+        /// Fills an array with random numbers within a specified range.
+        /// </summary>
+        /// <param name="values">The array to fill with random values.</param>
+        /// <param name="maxExclusive">The exclusive upper bound of the random number returned.</param>
+        public void NextInt32s(int[] values, int maxExclusive)
+        {
+            if (maxExclusive == int.MaxValue)
+            {
+                NextInt32s(values);
+                return;
+            }
+
+            if (_threadSafe)
+            {
+                lock (_lock)
+                {
+                    for (var i = 0; i < values.Length; i++)
+                    {
+                        values[i] = DoSampleInteger(maxExclusive);
+                    }
+                }
+            }
+            else
+            {
+                for (var i = 0; i < values.Length; i++)
+                {
+                    values[i] = DoSampleInteger(maxExclusive);
+                }
+            }
+        }
+
         /// <summary>
         /// Fills an array with random numbers within a specified range.
         /// </summary>
@@ -253,6 +290,18 @@ namespace MathNet.Numerics.Random
                 return;
             }
 
+            if (minInclusive == 0)
+            {
+                if (maxExclusive == int.MaxValue)
+                {
+                    NextInt32s(values);
+                    return;
+                }
+
+                NextInt32s(values, maxExclusive);
+                return;
+            }
+
             if (_threadSafe)
             {
                 lock (_lock)
@@ -389,16 +438,6 @@ namespace MathNet.Numerics.Random
             return (int)(DoSample() * int.MaxValue);
         }
 
-        /// <summary>
-        /// Returns a random 32-bit signed integer within the specified range.
-        /// </summary>
-        /// <param name="minInclusive">The inclusive lower bound of the random number returned.</param>
-        /// <param name="maxExclusive">The exclusive upper bound of the random number returned. <paramref name="maxExclusive"/> must be greater than or equal to <paramref name="minInclusive"/>.</param>
-        protected virtual int DoSampleInteger(int minInclusive, int maxExclusive)
-        {
-            return (int)(DoSample()*(maxExclusive - minInclusive)) + minInclusive;
-        }
-
         /// <summary>
         /// Fills the elements of a specified array of bytes with random numbers in full range, including zero and 255 (<see cref="F:System.Byte.MaxValue"/>).
         /// </summary>
@@ -409,5 +448,24 @@ namespace MathNet.Numerics.Random
                 buffer[i] = (byte)(DoSampleInteger() % 256);
             }
         }
+
+        /// <summary>
+        /// Returns a random 32-bit signed integer within the specified range.
+        /// </summary>
+        /// <param name="maxExclusive">The exclusive upper bound of the random number returned.</param>
+        protected virtual int DoSampleInteger(int maxExclusive)
+        {
+            return (int)(DoSample() * maxExclusive);
+        }
+
+        /// <summary>
+        /// Returns a random 32-bit signed integer within the specified range.
+        /// </summary>
+        /// <param name="minInclusive">The inclusive lower bound of the random number returned.</param>
+        /// <param name="maxExclusive">The exclusive upper bound of the random number returned. <paramref name="maxExclusive"/> must be greater than or equal to <paramref name="minInclusive"/>.</param>
+        protected virtual int DoSampleInteger(int minInclusive, int maxExclusive)
+        {
+            return DoSampleInteger(maxExclusive - minInclusive) + minInclusive;
+        }
     }
 }
diff --git a/src/Numerics/Random/SystemRandomSource.cs b/src/Numerics/Random/SystemRandomSource.cs
index 272f3c07..04c0dee0 100644
--- a/src/Numerics/Random/SystemRandomSource.cs
+++ b/src/Numerics/Random/SystemRandomSource.cs
@@ -126,6 +126,11 @@ namespace MathNet.Numerics.Random
             return _random.Next();
         }
 
+        protected override int DoSampleInteger(int maxExclusive)
+        {
+            return _random.Next(maxExclusive);
+        }
+
         /// <summary>
         /// Returns a random 32-bit signed integer within the specified range.
         /// </summary>