all CRCs in one place

CUETools.Codecs/CRCs/CRC16.cs

@@ -0,0 +1,50 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace CUETools.Codecs
+{
+	public class Crc16
+	{
+		ushort[] table = new ushort[256];
+
+		public ushort ComputeChecksum(byte[] bytes, int pos, int count)
+		{
+			ushort crc = 0;
+			for (int i = pos; i < pos + count; i++)
+			{
+				crc = (ushort)(((crc << 8) & 0xffff) ^ table[(crc >> 8) ^ bytes[i]]);
+			}
+			return crc;
+		}
+
+		public unsafe ushort ComputeChecksum(byte* bytes, int pos, int count)
+		{
+			ushort crc = 0;
+			fixed (ushort* t = table)
+				for (int i = pos; i < pos + count; i++)
+					crc = (ushort)(((crc << 8) & 0xffff) ^ t[(crc >> 8) ^ bytes[i]]);
+			return crc;
+		}
+
+		public Crc16()
+		{
+			int bits = 16;
+			int poly16 = 0x8005;
+			int poly = (poly16 + (1 << bits));
+			for (ushort i = 0; i < table.Length; i++)
+			{
+				int crc = i;
+				for (int j = 0; j < bits; j++)
+				{
+					if ((crc & (1U << (bits - 1))) != 0)
+						crc = ((crc << 1) ^ poly);
+					else
+						crc <<= 1;
+				}
+			        //table[i] = (crc & ((1<<bits)-1));
+				table[i] = (ushort)(crc & 0xffff);
+			}
+		}
+	}
+}