From 0acfff00771d0f944db0c91ebd366e0cb3d01591 Mon Sep 17 00:00:00 2001
From: Alexey 'Cluster' Avdyukhin <clusterrr@clusterrr.com>
Date: Tue, 8 Nov 2022 10:53:44 +0400
Subject: Padding fix, checksum fix

---
 Crc32.cs | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)
 create mode 100644 Crc32.cs

(limited to 'Crc32.cs')

diff --git a/Crc32.cs b/Crc32.cs
new file mode 100644
index 0000000..33acf83
--- /dev/null
+++ b/Crc32.cs
@@ -0,0 +1,65 @@
+using System;
+using System.Security.Cryptography;
+
+namespace com.clusterrr.Famicom.Containers
+{
+    /// <summary>
+    /// CRC32 calculator
+    /// </summary>
+    internal class Crc32 : HashAlgorithm
+    {
+        private readonly uint[] table = new uint[256];
+        private uint crc = 0xFFFFFFFF;
+
+        public Crc32()
+        {
+            // Calculate table
+            uint poly = 0xedb88320;
+            uint temp;
+            for (uint i = 0; i < table.Length; ++i)
+            {
+                temp = i;
+                for (int j = 8; j > 0; --j)
+                {
+                    if ((temp & 1) == 1)
+                    {
+                        temp = (uint)((temp >> 1) ^ poly);
+                    }
+                    else
+                    {
+                        temp >>= 1;
+                    }
+                }
+                table[i] = temp;
+            }
+        }
+
+        public override void Initialize()
+        {
+        }
+
+        public override bool CanReuseTransform => false;
+
+        protected override void HashCore(byte[] array, int ibStart, int cbSize)
+        {
+            while (cbSize > 0)
+            {
+                var pos = ibStart;
+                byte index = (byte)(((crc) & 0xff) ^ array[pos]);
+                crc = (crc >> 8) ^ table[index];
+                ibStart++;
+                cbSize--;
+            }
+        }
+
+        protected override byte[] HashFinal()
+        {
+            return BitConverter.GetBytes(~crc);
+        }
+
+        public override bool CanTransformMultipleBlocks => true;
+        public override byte[] Hash => BitConverter.GetBytes(~crc);
+        public override int HashSize => 32;
+
+    }
+}
-- 
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