Save Common implementation (#434)

* save common implementation

* remove zero userid check

* Renamed UserId to UInt128

* fix index in hex conversion

Ryujinx.HLE/Utilities/UInt128.cs

@@ -0,0 +1,61 @@
+using Ryujinx.HLE.Utilities;
+using System;
+using System.IO;
+using System.Linq;
+
+namespace Ryujinx.HLE.Utilities
+{
+    public struct UInt128
+    {
+        public long High { get; private set; }
+        public long Low  { get; private set; }
+
+        public UInt128(long Low, long High)
+        {
+            this.Low  = Low;
+            this.High = High;
+
+            byte[] Bytes = new byte[16];
+
+            int Index = Bytes.Length;
+
+            void WriteBytes(long Value)
+            {
+                for (int Byte = 0; Byte < 8; Byte++)
+                {
+                    Bytes[--Index] = (byte)(Value >> Byte * 8);
+                }
+            }
+
+            WriteBytes(Low);
+            WriteBytes(High);
+        }
+
+        public UInt128(string UInt128Hex)
+        {
+            if (UInt128Hex == null || UInt128Hex.Length != 32 || !UInt128Hex.All("0123456789abcdefABCDEF".Contains))
+            {
+                throw new ArgumentException("Invalid Hex value!", nameof(UInt128Hex));
+            }
+
+            Low  = Convert.ToInt64(UInt128Hex.Substring(16),16);
+            High = Convert.ToInt64(UInt128Hex.Substring(0, 16), 16);
+        }
+
+        public void Write(BinaryWriter BinaryWriter)
+        {
+            BinaryWriter.Write(High);
+            BinaryWriter.Write(Low);
+        }
+
+        public override string ToString()
+        {
+            return High.ToString("x16") + Low.ToString("x16");
+        }
+
+        public bool IsZero()
+        {
+            return (Low | High) == 0;
+        }
+    }
+}