From 85e93024a9de579615558420bc442edbab05c5c7 Mon Sep 17 00:00:00 2001
From: Simon Cropp <simon.cropp@gmail.com>
Date: Tue, 14 Jul 2026 22:16:48 +1000
Subject: [PATCH] use System.IO.Hashing

---
 src/Directory.Build.props              |  2 +-
 src/Directory.Packages.props           |  1 +
 src/Verify.DocNet/GlobalUsings.cs      |  1 +
 src/Verify.DocNet/PngEncoder.cs        | 53 +++-----------------------
 src/Verify.DocNet/Verify.DocNet.csproj |  1 +
 5 files changed, 9 insertions(+), 49 deletions(-)

diff --git a/src/Directory.Build.props b/src/Directory.Build.props
index 3eb957b..c9eea03 100644
--- a/src/Directory.Build.props
+++ b/src/Directory.Build.props
@@ -2,7 +2,7 @@
 <Project>
   <PropertyGroup>
     <NoWarn>CS1591;CS0649;NU1608;NU1109</NoWarn>
-    <Version>3.3.1</Version>
+    <Version>3.3.2</Version>
     <AssemblyVersion>1.0.0</AssemblyVersion>
     <LangVersion>preview</LangVersion>
     <SignAssembly>false</SignAssembly>
diff --git a/src/Directory.Packages.props b/src/Directory.Packages.props
index b8189ee..acfb955 100644
--- a/src/Directory.Packages.props
+++ b/src/Directory.Packages.props
@@ -5,6 +5,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageVersion Include="Docnet.Core" Version="2.6.0" />
+    <PackageVersion Include="System.IO.Hashing" Version="10.0.9" />
     <PackageVersion Include="Magick.NET-Q16-AnyCPU" Version="14.14.0" />
     <PackageVersion Include="MarkdownSnippets.MsBuild" Version="28.4.1" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.7.0" />
diff --git a/src/Verify.DocNet/GlobalUsings.cs b/src/Verify.DocNet/GlobalUsings.cs
index c64bf4e..f21bb70 100644
--- a/src/Verify.DocNet/GlobalUsings.cs
+++ b/src/Verify.DocNet/GlobalUsings.cs
@@ -1,5 +1,6 @@
 global using System.Buffers.Binary;
 global using System.IO.Compression;
+global using System.IO.Hashing;
 global using Docnet.Core;
 global using Docnet.Core.Converters;
 global using Docnet.Core.Models;
diff --git a/src/Verify.DocNet/PngEncoder.cs b/src/Verify.DocNet/PngEncoder.cs
index 8659d96..b3049b1 100644
--- a/src/Verify.DocNet/PngEncoder.cs
+++ b/src/Verify.DocNet/PngEncoder.cs
@@ -69,55 +69,12 @@ static void WriteChunk(Stream stream, ReadOnlySpan<byte> type, ReadOnlySpan<byte
         stream.Write(type);
         stream.Write(data);
 
+        // CRC covers the chunk type followed by its data (CRC-32/ISO-HDLC, as PNG requires).
+        var hasher = new Crc32();
+        hasher.Append(type);
+        hasher.Append(data);
         Span<byte> crc = stackalloc byte[4];
-        BinaryPrimitives.WriteUInt32BigEndian(crc, Crc32.Compute(type, data));
+        BinaryPrimitives.WriteUInt32BigEndian(crc, hasher.GetCurrentHashAsUInt32());
         stream.Write(crc);
     }
-
-    static class Crc32
-    {
-        static uint[] table = BuildTable();
-
-        static uint[] BuildTable()
-        {
-            var table = new uint[256];
-            for (var n = 0; n < 256; n++)
-            {
-                var c = (uint)n;
-                for (var k = 0; k < 8; k++)
-                {
-                    if ((c & 1) == 0)
-                    {
-                        c >>= 1;
-                    }
-                    else
-                    {
-                        c = 0xEDB88320 ^ (c >> 1);
-                    }
-                }
-
-                table[n] = c;
-            }
-
-            return table;
-        }
-
-        public static uint Compute(ReadOnlySpan<byte> type, ReadOnlySpan<byte> data)
-        {
-            var crc = 0xFFFFFFFFu;
-            crc = Update(crc, type);
-            crc = Update(crc, data);
-            return crc ^ 0xFFFFFFFFu;
-        }
-
-        static uint Update(uint crc, ReadOnlySpan<byte> data)
-        {
-            foreach (var b in data)
-            {
-                crc = table[(crc ^ b) & 0xFF] ^ (crc >> 8);
-            }
-
-            return crc;
-        }
-    }
 }
diff --git a/src/Verify.DocNet/Verify.DocNet.csproj b/src/Verify.DocNet/Verify.DocNet.csproj
index 900da4b..94f384f 100644
--- a/src/Verify.DocNet/Verify.DocNet.csproj
+++ b/src/Verify.DocNet/Verify.DocNet.csproj
@@ -5,6 +5,7 @@
   <ItemGroup>
     <InternalsVisibleTo Include="Tests" />
     <PackageReference Include="Docnet.Core" />
+    <PackageReference Include="System.IO.Hashing" />
     <PackageReference Include="Verify" />
     <PackageReference Include="ProjectDefaults" PrivateAssets="all" />
     <PackageReference Include="Microsoft.Sbom.Targets" PrivateAssets="all" Condition="'$(CI)' == 'true'" />