BytesUtility：增加 CRC16 方法。

Apewer/BytesUtility.cs

@@ -1079,6 +1079,9 @@ namespace Apewer
         /// <summary>获取 SHA512 值。</summary>
         public static byte[] SHA512(this Stream stream, Action<long> progress = null) => ComputeHash<SHA512CryptoServiceProvider>(stream, progress);
 
+        /// <summary>计算 CRC16 校验和。</summary>
+        public static ushort CRC16(this byte[] bytes) => Internals.CRC16.Instance.Compute(bytes);
+
         #endregion
 
     }

Apewer/Internals/CRC16.cs

@@ -0,0 +1,54 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Apewer.Internals
+{
+
+    class CRC16
+    {
+
+        public static CRC16 Instance = new CRC16();
+
+        const ushort origin = 0xFFFF;
+        const ushort polynomial = 0xA001;
+
+        ushort[] table = new ushort[256];
+
+        public CRC16()
+        {
+            ushort value, temp;
+            for (ushort i = 0; i < table.Length; ++i)
+            {
+                value = 0;
+                temp = i;
+                for (byte j = 0; j < 8; ++j)
+                {
+                    if (((value ^ temp) & 0x0001) != 0)
+                    {
+                        value = (ushort)((value >> 1) ^ polynomial);
+                    }
+                    else
+                    {
+                        value >>= 1;
+                    }
+                    temp >>= 1;
+                }
+                table[i] = value;
+            }
+        }
+
+        public ushort Compute(byte[] bytes)
+        {
+            ushort crc = origin;
+            for (int i = 0; i < bytes.Length; ++i)
+            {
+                byte index = (byte)(crc ^ bytes[i]);
+                crc = (ushort)((crc >> 8) ^ table[index]);
+            }
+            return crc;
+        }
+
+    }
+
+}