Add AppContext switch to allow hash seed to be deterministic (#79)

rubo · web-flow · commit 897ba8f2e407 · 2026-01-07T13:49:53.000+01:00
diff --git a/src/Directory.Build.props b/src/Directory.Build.props
@@ -12,8 +12,8 @@
   <PropertyGroup Label="ProductInfo">
     <Authors>Nethermind</Authors>
     <Copyright>Demerzel Solutions Limited</Copyright>
-    <VersionPrefix>1.4.0</VersionPrefix>
-    <VersionSuffix></VersionSuffix>
+    <VersionPrefix>1.5.0</VersionPrefix>
+    <VersionSuffix>preview.1</VersionSuffix>
   </PropertyGroup>
 
 </Project>
diff --git a/src/Nethermind.Int256.Tests/UInt256Tests.cs b/src/Nethermind.Int256.Tests/UInt256Tests.cs
@@ -852,4 +852,14 @@ public void ComparisonOperators((BigInteger A, BigInteger B) test)
             (uint256a == b).Should().Be(test.A == b);
         }
     }
+
+    [NonParallelizable]
+    [TestCase(false)]
+    [TestCase(true)]
+    public void Shoud_respect_appcontext_switch(bool useHashCodeRandomizer)
+    {
+        AppContext.SetSwitch("Nethermind.Int256.UseHashCodeRandomizer", useHashCodeRandomizer);
+
+        Assert.That(UInt256.UseHashCodeRandomizer, Is.EqualTo(useHashCodeRandomizer));
+    }
 }
diff --git a/src/Nethermind.Int256/UInt256.cs b/src/Nethermind.Int256/UInt256.cs
@@ -10,6 +10,7 @@
 using System.Runtime.Intrinsics;
 using System.Runtime.Intrinsics.Arm;
 using System.Runtime.Intrinsics.X86;
+using System.Security.Cryptography;
 
 [assembly: InternalsVisibleTo("Nethermind.Int256.Tests")]
 
@@ -22,7 +23,13 @@ namespace Nethermind.Int256;
     // Ensure that hashes are different for every run of the node and every node, so if are any hash collisions on
     // one node they will not be the same on another node or across a restart so hash collision cannot be used to degrade
     // the performance of the network as a whole.
-    private static readonly uint s_instanceRandom = (uint)System.Security.Cryptography.RandomNumberGenerator.GetInt32(int.MinValue, int.MaxValue);
+    // Constant by default for zkVM-compatibility -- subject to change in the near feature
+    private static readonly uint _hashSeed = UseHashCodeRandomizer
+        ? (uint)RandomNumberGenerator.GetInt32(int.MinValue, int.MaxValue)
+        : 2098026241U; // just a random prime number
+
+    [FeatureSwitchDefinition("Nethermind.Int256.UseHashCodeRandomizer")]
+    public static bool UseHashCodeRandomizer => AppContext.TryGetSwitch("Nethermind.Int256.UseHashCodeRandomizer", out var useHashCodeRandomizer) && useHashCodeRandomizer;
 
     public static readonly UInt256 Zero = 0ul;
     public static readonly UInt256 One = 1ul;
@@ -1396,7 +1403,7 @@ public override int GetHashCode()
         // Very fast hardware accelerated non-cryptographic hash function
 
         // Start with instance random, length and first ulong as seed
-        uint hash = BitOperations.Crc32C(s_instanceRandom, u0);
+        uint hash = BitOperations.Crc32C(_hashSeed, u0);
 
         // Crc32C is 3 cycle latency, 1 cycle throughput
         // So we use same initial 3 times to not create a dependency chain

Original file line number	Diff line number	Diff line change
`@@ -852,4 +852,14 @@ public void ComparisonOperators((BigInteger A, BigInteger B) test)`
`852`	`852`	`(uint256a == b).Should().Be(test.A == b);`
`853`	`853`	`}`
`854`	`854`	`}`
	`855`	`+`
	`856`	`+ [NonParallelizable]`
	`857`	`+ [TestCase(false)]`
	`858`	`+ [TestCase(true)]`
	`859`	`+ public void Shoud_respect_appcontext_switch(bool useHashCodeRandomizer)`
	`860`	`+ {`
	`861`	`+ AppContext.SetSwitch("Nethermind.Int256.UseHashCodeRandomizer", useHashCodeRandomizer);`
	`862`	`+`
	`863`	`+ Assert.That(UInt256.UseHashCodeRandomizer, Is.EqualTo(useHashCodeRandomizer));`
	`864`	`+ }`
`855`	`865`	`}`