Use Marvin32 instead of xxHash32 in COSE hash codes

dotnet · Sep 17, 2024 · 750a230 · 750a230
1 parent 5bb9659
commit 750a230
Show file tree

Hide file tree

Showing 3 changed files with 43 additions and 35 deletions.
diff --git a/src/libraries/Common/src/System/HashCodeRandomization.cs b/src/libraries/Common/src/System/HashCodeRandomization.cs
@@ -1,6 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Runtime.InteropServices;
+using System.Security.Cryptography;
+
 namespace System
 {
     // Contains helpers for calculating randomized hash codes of common types.
@@ -21,32 +24,11 @@ public static int GetRandomizedOrdinalHashCode(this string value)
 
             return value.GetHashCode();
 #else
-            // Downlevel, we need to perform randomization ourselves. There's still
-            // the potential for limited collisions ("Hello!" and "Hello!\0"), but
-            // this shouldn't be a problem in practice. If we need to address it,
-            // we can mix the string length into the accumulator before running the
-            // string contents through.
-            //
-            // We'll pull out pairs of chars and write 32 bits at a time.
+            // Downlevel, we need to perform randomization ourselves.
 
-            HashCode hashCode = default;
-            int pair = 0;
-            for (int i = 0; i < value.Length; i++)
-            {
-                int ch = value[i];
-                if ((i & 1) == 0)
-                {
-                    pair = ch << 16; // first member of pair
-                }
-                else
-                {
-                    pair |= ch; // second member of pair
-                    hashCode.Add(pair); // write pair as single unit
-                    pair = 0;
-                }
-            }
-            hashCode.Add(pair); // flush any leftover data (could be 0 or 1 chars)
-            return hashCode.ToHashCode();
+            ReadOnlySpan<char> charSpan = value.AsSpan();
+            ReadOnlySpan<byte> byteSpan = MemoryMarshal.AsBytes(charSpan);
+            return Marvin.ComputeHash32(byteSpan, Marvin.DefaultSeed);
 #endif
         }
 

diff --git a/src/libraries/System.Private.CoreLib/src/System/Marvin.cs b/src/libraries/System.Private.CoreLib/src/System/Marvin.cs
@@ -6,6 +6,12 @@
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
+#if SYSTEM_PRIVATE_CORELIB
+using static System.Numerics.BitOperations;
+#else
+using System.Security.Cryptography;
+#endif
+
 namespace System
 {
     internal static partial class Marvin
@@ -204,7 +210,7 @@ public static int ComputeHash32(ref byte data, uint count, uint p0, uint p1)
                 else
                 {
                     partialResult |= (uint)Unsafe.ReadUnaligned<ushort>(ref data);
-                    partialResult = BitOperations.RotateLeft(partialResult, 16);
+                    partialResult = RotateLeft(partialResult, 16);
                 }
             }
 
@@ -221,16 +227,16 @@ private static void Block(ref uint rp0, ref uint rp1)
             uint p1 = rp1;
 
             p1 ^= p0;
-            p0 = BitOperations.RotateLeft(p0, 20);
+            p0 = RotateLeft(p0, 20);
 
             p0 += p1;
-            p1 = BitOperations.RotateLeft(p1, 9);
+            p1 = RotateLeft(p1, 9);
 
             p1 ^= p0;
-            p0 = BitOperations.RotateLeft(p0, 27);
+            p0 = RotateLeft(p0, 27);
 
             p0 += p1;
-            p1 = BitOperations.RotateLeft(p1, 19);
+            p1 = RotateLeft(p1, 19);
 
             rp0 = p0;
             rp1 = p1;
@@ -241,8 +247,29 @@ private static void Block(ref uint rp0, ref uint rp1)
         private static unsafe ulong GenerateSeed()
         {
             ulong seed;
+#if SYSTEM_PRIVATE_CORELIB
             Interop.GetRandomBytes((byte*)&seed, sizeof(ulong));
+#else
+            byte[] seedBytes = new byte[sizeof(ulong)];
+            using (RandomNumberGenerator rng = RandomNumberGenerator.Create())
+            {
+                rng.GetBytes(seedBytes);
+                fixed (byte* b = seedBytes)
+                {
+                    seed = *(ulong*)b;
+                }
+            }
+#endif
             return seed;
         }
+
+#if !SYSTEM_PRIVATE_CORELIB
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static uint RotateLeft(uint value, int shift)
+        {
+            // This is expected to be optimized into a single rol (or ror with negated shift value) instruction
+            return (value << shift) | (value >> (32 - shift));
+        }
+#endif
     }
 }
diff --git a/src/libraries/System.Security.Cryptography.Cose/src/System.Security.Cryptography.Cose.csproj b/src/libraries/System.Security.Cryptography.Cose/src/System.Security.Cryptography.Cose.csproj
@@ -36,13 +36,12 @@
     <Compile Include="System\Security\Cryptography\Cose\SigStructureContext.cs" />
   </ItemGroup>
 
-  <ItemGroup>
-    <ProjectReference Include="$(LibrariesProjectRoot)System.Formats.Cbor\src\System.Formats.Cbor.csproj" />
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' != '.NETCoreApp'">
+      <Compile Include="$(CoreLibSharedDir)System\Marvin.cs" Link="CoreLib\System\Marvin.cs" />
   </ItemGroup>
 
-  <!-- For System.HashCode -->
-  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' != '.NETCoreApp'">
-    <PackageReference Include="Microsoft.Bcl.HashCode" Version="$(MicrosoftBclHashCodeVersion)" />
+  <ItemGroup>
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Formats.Cbor\src\System.Formats.Cbor.csproj" />
   </ItemGroup>
 
 </Project>