Added missing file PngCrc.cs

Ambermoon.Common/PngCrc.cs

@@ -0,0 +1,67 @@
+namespace Ambermoon
+{
+    public class PngCrc
+    {
+        uint[] table = null;
+        uint lastCrc = 0;
+
+        void EnsureTable()
+        {
+            if (table != null)
+                return;
+
+            table = new uint[256];
+            uint c;
+            uint k;
+
+            for (uint n = 0; n < 256; ++n)
+            {
+                c = n;
+
+                for (k = 0; k < 8; ++k)
+                {
+                    if ((c & 1) != 0)
+                        c = 0xedb88320 ^ (c >> 1);
+                    else
+                        c >>= 1;
+                }
+
+                table[n] = c;
+            }
+        }
+
+        uint Update(uint crc, byte[] buffer, int length)
+        {
+            EnsureTable();
+            uint c = crc;
+
+            for (int n = 0; n < length; ++n)
+            {
+                c = table[(c ^ buffer[n]) & 0xff] ^ (c >> 8);
+            }
+
+            return c;
+        }
+
+        public uint Calculate(byte[] buffer)
+        {
+            return Calculate(buffer, buffer.Length);
+        }
+
+        public uint Calculate(byte[] buffer, int length)
+        {
+            return lastCrc = Update(lastCrc ^ 0xffffffff, buffer, length) ^ 0xffffffff;
+        }
+
+        public uint Calculate(uint crc, byte[] buffer)
+        {
+            return Calculate(crc, buffer, buffer.Length);
+        }
+
+        public uint Calculate(uint crc, byte[] buffer, int length)
+        {
+            lastCrc = crc;
+            return Calculate(buffer, length);
+        }
+    }
+}