Cardiff.cs

using System.Buffers.Binary;
using System.Diagnostics;
using System.Linq;
using System.Text;

namespace Wales
{
    class Cardiff
    {
        private static List<Range> ReadBomHeaderAndIndex(BinaryReader reader)
        {
            var bomStoreMarker = reader.ReadBytes(8);
            if (!bomStoreMarker.SequenceEqual(new byte[] { (byte)'B', (byte)'O', (byte)'M', (byte)'S', (byte)'t', (byte)'o', (byte)'r', (byte)'e'}))
                throw new FormatException("Not a BOM file");
            var bomStoreVersion = BinaryPrimitives.ReverseEndianness(reader.ReadUInt32());
            if (bomStoreVersion != 1)
                throw new FormatException("Unknown BOM file version");
            var bomStoreNumberOfBlocks = BinaryPrimitives.ReverseEndianness(reader.ReadUInt32());
            var bomStoreIndexOffset = BinaryPrimitives.ReverseEndianness(reader.ReadUInt32());

            // Read index table
            reader.BaseStream.Seek(bomStoreIndexOffset, SeekOrigin.Begin);
            var bomIndexCount = BinaryPrimitives.ReverseEndianness(reader.ReadUInt32());
            var bomIndex = new List<Range>((int)bomIndexCount);
            for (int i = 0; i < bomIndexCount && i <= bomStoreNumberOfBlocks; i++)
            {
                var offset = BinaryPrimitives.ReverseEndianness(reader.ReadUInt32());
                var length = BinaryPrimitives.ReverseEndianness(reader.ReadUInt32());
                bomIndex.Add(new Range((int)offset, (int)offset + (int)length));
            }

            return bomIndex;
        }

        private static bool CompareByteRange(BinaryReader reader1, BinaryReader reader2, Range range)
        {
            if (range.End.Value != range.Start.Value)
            {
                reader1.BaseStream.Seek(range.Start.Value, SeekOrigin.Begin);
                reader2.BaseStream.Seek(range.Start.Value, SeekOrigin.Begin);
                var contents1 = reader1.ReadBytes(range.End.Value - range.Start.Value);
                var contents2 = reader2.ReadBytes(range.End.Value - range.Start.Value);

                // For CTSI blocks use semantic comparison
                if (contents1.Length >= 0xa8 && contents1.Take(4).SequenceEqual(new byte[] { (byte)'I', (byte)'S', (byte)'T', (byte)'C' }))
                {
                    // Compare first 0x28 bytes of header
                    if (!contents1.AsSpan(0, 0x28).SequenceEqual(contents2.AsSpan(0, 0x28)))
                        return false;
                    // Compare 0-terminated file name
                    for (int i = 0; i < 0x80; i++)
                    {
                        if (contents1[0x28 + i] != contents2[0x28 + i])
                            return false;
                        if (contents1[0x28 + i] == 0)
                            break;
                    }
                    // Compare reminder of the data
                    return contents1.AsSpan(0xa8).SequenceEqual(contents2.AsSpan(0xa8));
                }
                else
                {
                    return contents1.AsSpan().SequenceEqual(contents2.AsSpan());
                }
            }

            return true;
        }

        static int Main(string[] args)
        {
            try
            {
                using var reader1 = new BinaryReader(File.OpenRead(args[0]));
                var bomIndex1 = ReadBomHeaderAndIndex(reader1);
                using var reader2 = new BinaryReader(File.OpenRead(args[1]));
                var bomIndex2 = ReadBomHeaderAndIndex(reader2);

                if (!bomIndex1.SequenceEqual(bomIndex2))
                {
                    Console.WriteLine("BOM index differs");
                    return 1;
                }

                int i = 0;
                foreach (var range in bomIndex1)
                {
                    if (!CompareByteRange(reader1, reader2, range))
                    {
                        Console.WriteLine($"Content different in block {i} {range.Start:x}-{range.End:x}");
                        return 1;
                    }
                    i++;
                }

                Console.WriteLine($"Files are semantically identical");
                return 0;
            }
            catch (Exception e)
            {
                Console.WriteLine(e.ToString());
                return 1;
            }
        }
    }
}