From 632b11ef2b3a5400f29caf5f49bcd20051bf342a Mon Sep 17 00:00:00 2001
From: Matt Nadareski <mnadareski@outlook.com>
Date: Sun, 24 Mar 2024 18:35:04 -0400
Subject: [PATCH] Correctly label CRC64 implementations, extend to old .NET

---
 SabreTools.Hashing.Test/HashToolTests.cs | 20 +++++---------------
 SabreTools.Hashing/HashType.cs           |  8 +++-----
 SabreTools.Hashing/HashWrapper.cs        |  9 ++++++++-
 3 files changed, 16 insertions(+), 21 deletions(-)

diff --git a/SabreTools.Hashing.Test/HashToolTests.cs b/SabreTools.Hashing.Test/HashToolTests.cs
index 0da0b86..cb3d08f 100644
--- a/SabreTools.Hashing.Test/HashToolTests.cs
+++ b/SabreTools.Hashing.Test/HashToolTests.cs
@@ -18,10 +18,8 @@ namespace SabreTools.Hashing.Test
         private const string _crc16_ccitt = "482d";
         private const string _crc16_ibm = "7573";
         private const string _crc32 = "ba02a660";
-#if NET462_OR_GREATER || NETCOREAPP
         private const string _crc64 = "a0e0009c18b5338d";
-#endif
-        private const string _crc64_ecma = "fb49044e8331f6e5";
+        private const string _crc64_reversed = "fb49044e8331f6e5";
         private const string _fletcher16 = "46c1";
         private const string _fletcher32 = "073f2d94";
         private const string _md5 = "b722871eaa950016296184d026c5dec9";
@@ -71,10 +69,8 @@ namespace SabreTools.Hashing.Test
             Assert.Equal(_crc32, hashDict[HashType.CRC32_Naive]);
             Assert.Equal(_crc32, hashDict[HashType.CRC32_Optimized]);
             Assert.Equal(_crc32, hashDict[HashType.CRC32_Parallel]);
-#if NET462_OR_GREATER || NETCOREAPP
             Assert.Equal(_crc64, hashDict[HashType.CRC64]);
-#endif
-            Assert.Equal(_crc64_ecma, hashDict[HashType.CRC64_ECMA]);
+            Assert.Equal(_crc64_reversed, hashDict[HashType.CRC64_Reversed]);
             Assert.Equal(_fletcher16, hashDict[HashType.Fletcher16]);
             Assert.Equal(_fletcher32, hashDict[HashType.Fletcher32]);
             Assert.Equal(_md5, hashDict[HashType.MD5]);
@@ -112,10 +108,8 @@ namespace SabreTools.Hashing.Test
             Assert.Equal(_crc32, hashDict[HashType.CRC32_Naive]);
             Assert.Equal(_crc32, hashDict[HashType.CRC32_Optimized]);
             Assert.Equal(_crc32, hashDict[HashType.CRC32_Parallel]);
-#if NET462_OR_GREATER || NETCOREAPP
             Assert.Equal(_crc64, hashDict[HashType.CRC64]);
-#endif
-            Assert.Equal(_crc64_ecma, hashDict[HashType.CRC64_ECMA]);
+            Assert.Equal(_crc64_reversed, hashDict[HashType.CRC64_Reversed]);
             Assert.Equal(_fletcher16, hashDict[HashType.Fletcher16]);
             Assert.Equal(_fletcher32, hashDict[HashType.Fletcher32]);
             Assert.Equal(_md5, hashDict[HashType.MD5]);
@@ -150,10 +144,8 @@ namespace SabreTools.Hashing.Test
             Assert.Equal(_crc32, hashDict[HashType.CRC32_Naive]);
             Assert.Equal(_crc32, hashDict[HashType.CRC32_Optimized]);
             Assert.Equal(_crc32, hashDict[HashType.CRC32_Parallel]);
-#if NET462_OR_GREATER || NETCOREAPP
             Assert.Equal(_crc64, hashDict[HashType.CRC64]);
-#endif
-            Assert.Equal(_crc64_ecma, hashDict[HashType.CRC64_ECMA]);
+            Assert.Equal(_crc64_reversed, hashDict[HashType.CRC64_Reversed]);
             Assert.Equal(_fletcher16, hashDict[HashType.Fletcher16]);
             Assert.Equal(_fletcher32, hashDict[HashType.Fletcher32]);
             Assert.Equal(_md5, hashDict[HashType.MD5]);
@@ -188,10 +180,8 @@ namespace SabreTools.Hashing.Test
             Assert.Equal(_crc32, hashDict[HashType.CRC32_Naive]);
             Assert.Equal(_crc32, hashDict[HashType.CRC32_Optimized]);
             Assert.Equal(_crc32, hashDict[HashType.CRC32_Parallel]);
-#if NET462_OR_GREATER || NETCOREAPP
             Assert.Equal(_crc64, hashDict[HashType.CRC64]);
-#endif
-            Assert.Equal(_crc64_ecma, hashDict[HashType.CRC64_ECMA]);
+            Assert.Equal(_crc64_reversed, hashDict[HashType.CRC64_Reversed]);
             Assert.Equal(_fletcher16, hashDict[HashType.Fletcher16]);
             Assert.Equal(_fletcher32, hashDict[HashType.Fletcher32]);
             Assert.Equal(_md5, hashDict[HashType.MD5]);
diff --git a/SabreTools.Hashing/HashType.cs b/SabreTools.Hashing/HashType.cs
index 023f268..a014996 100644
--- a/SabreTools.Hashing/HashType.cs
+++ b/SabreTools.Hashing/HashType.cs
@@ -53,17 +53,15 @@ namespace SabreTools.Hashing
         /// </summary>
         CRC32_Parallel,
 
-#if NET462_OR_GREATER || NETCOREAPP
         /// <summary>
-        /// CRC 64-bit checksum
+        /// CRC 64-bit checksum (0x42F0E1EBA9EA3693 polynomial)
         /// </summary>
         CRC64,
-#endif
 
         /// <summary>
-        /// CRC 64-bit checksum (ECMA implementation)
+        /// CRC 64-bit checksum (0xC96C5795D7870F42 polynomial)
         /// </summary>
-        CRC64_ECMA,
+        CRC64_Reversed,
 
         /// <summary>
         /// John G. Fletcher's 16-bit checksum
diff --git a/SabreTools.Hashing/HashWrapper.cs b/SabreTools.Hashing/HashWrapper.cs
index 5169885..ad03128 100644
--- a/SabreTools.Hashing/HashWrapper.cs
+++ b/SabreTools.Hashing/HashWrapper.cs
@@ -76,6 +76,11 @@ namespace SabreTools.Hashing
         /// <remarks>May be either a HashAlgorithm or NonCryptographicHashAlgorithm</remarks>
         private object? _hasher;
 
+        /// <summary>
+        /// Non-reversed CRC-64 polynomial
+        /// </summary>
+        private const ulong CRC64_ECMA_POLY_NORMAL = 0x42F0E1EBA9EA3693;
+
         #endregion
 
         #region Constructors
@@ -114,8 +119,10 @@ namespace SabreTools.Hashing
                 HashType.CRC32_Parallel => new ParallelCRC(),
 #if NET462_OR_GREATER || NETCOREAPP
                 HashType.CRC64 => new Crc64(),
+#else
+                HashType.CRC64 => new Crc64Context(CRC64_ECMA_POLY_NORMAL, 0xFFFFFFFFFFFFFFFF),
 #endif
-                HashType.CRC64_ECMA => new Crc64Context(),
+                HashType.CRC64_Reversed => new Crc64Context(),
                 HashType.Fletcher16 => new Fletcher16Context(),
                 HashType.Fletcher32 => new Fletcher32Context(),
                 HashType.MD5 => MD5.Create(),