CharaSaveDat.cs

using System;
using System.Data;
using System.IO;
using System.Linq;
using System.Text;

namespace FFXIVGenerateENPCSheet
{
    public class CharaSaveDat
    {
        public static byte[] Generate(byte[] originalLook, string msg)
        {
            byte[] buffer = new byte[0xD4];
            
            using (MemoryStream memstream = new MemoryStream(buffer))
            {
                using (BinaryWriter binwriter = new BinaryWriter(memstream))
                {
                    binwriter.Write(0x2013FF14); //Magic
                    binwriter.Write(0x03); //Version

                    memstream.Position = 0x10;
                    
                    binwriter.Write(originalLook); //Look data

                    memstream.Position = 0x30;
                    
                    binwriter.Write(Encoding.UTF8.GetBytes(msg));

                    byte[] toSum = new byte[0xD4];
                    Array.Copy(memstream.ToArray(), 0, toSum, 0, 0xD4);
                    int chksum = CalcChecksum(toSum);

                    memstream.Position = 0x8;
                    
                    binwriter.Write(chksum);
                }

                return memstream.ToArray();
            }
        }
        
        private static int CalcChecksum(byte[] data)
        {
            var checksum = 0;
            var prevY = 0;

            for (var offset = 0x10; offset < 0xD4; offset += 4)
            {
                var processed = offset - 0x10;

                var x = (data[offset + 2] << (processed - 24 * ((processed + 2) / 0x18) + 2)) ^
                        (data[offset + 1] << (processed - 24 * ((processed + 1) / 0x18) + 1));

                var y = (data[offset] << processed % 0x18) ^
                        (data[offset + 3] << (processed - 24 * ((processed + 3) / 0x18) + 3)) ^ x;

                checksum = y ^ prevY;
                prevY ^= y;
            }

            return checksum;
        }
    }
}