Simplify Random for ulong (#87219)

Use Math.BigMul instead of UInt128 since both values are always ulongs.
dotnet · Jun 8, 2023 · 5353824 · 5353824
1 parent c96c15c
commit 5353824
Showing 1 changed file with 4 additions and 5 deletions.
diff --git a/src/libraries/System.Private.CoreLib/src/System/Random.ImplBase.cs b/src/libraries/System.Private.CoreLib/src/System/Random.ImplBase.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System;
 using System.Runtime.CompilerServices;
 
 namespace System
@@ -57,21 +58,19 @@ internal static uint NextUInt32(uint maxValue, XoshiroImpl xoshiro)
             [MethodImpl(MethodImplOptions.AggressiveInlining)]
             internal static ulong NextUInt64(ulong maxValue, XoshiroImpl xoshiro)
             {
-                UInt128 randomProduct = (UInt128)maxValue * xoshiro.NextUInt64();
-                ulong lowPart = (ulong)randomProduct;
+                ulong randomProduct = Math.BigMul(maxValue, xoshiro.NextUInt64(), out ulong lowPart);
 
                 if (lowPart < maxValue)
                 {
                     ulong remainder = (0ul - maxValue) % maxValue;
 
                     while (lowPart < remainder)
                     {
-                        randomProduct = (UInt128)maxValue * xoshiro.NextUInt64();
-                        lowPart = (ulong)randomProduct;
+                        randomProduct = Math.BigMul(maxValue, xoshiro.NextUInt64(), out lowPart);
                     }
                 }
 
-                return (ulong)(randomProduct >> 64);
+                return randomProduct;
             }
         }
     }