ryubing-ryujinx/src/Ryujinx.HLE/Utilities/NacpHelper.cs

using System;
using System.Buffers.Binary;
using System.IO;
using System.IO.Compression;
using System.Runtime.InteropServices;
using LibHac.Ns;

namespace Ryujinx.HLE.Utilities
{
    public static class NacpHelper
    {
        private const int CompressedTitleCount = 32;
        private const int UncompressedTitleCount = 16;
        private const int TitleEntrySize = 0x300;
        private const int TitleCompressionByteIndex = 1; // offset within Reserved3214

        public static bool IsCompressed(ref readonly ApplicationControlProperty nacp)
            => nacp.Reserved3214[TitleCompressionByteIndex] == 1;

        public static int GetTitleCount(ref readonly ApplicationControlProperty nacp)
            => IsCompressed(in nacp) ? CompressedTitleCount : UncompressedTitleCount;

        /// <summary>
        /// Decompresses a zlib-compressed NACP title block into 32 title entries.
        /// Only call this when <see cref="IsCompressed"/> returns <c>true</c>.
        /// </summary>
        public static ApplicationControlProperty.ApplicationTitle[] DecompressTitleEntries(
            ref readonly ApplicationControlProperty nacp)
        {
            ReadOnlySpan<byte> titleBytes = MemoryMarshal.AsBytes(
                (ReadOnlySpan<ApplicationControlProperty.ApplicationTitle>)nacp.Title);

            ushort compressedBlobSize = BinaryPrimitives.ReadUInt16LittleEndian(titleBytes);
            ReadOnlySpan<byte> compressedBlob = titleBytes.Slice(2, compressedBlobSize);

            byte[] decompressed = new byte[CompressedTitleCount * TitleEntrySize];

            using (var compressedStream = new MemoryStream(compressedBlob.ToArray()))
            using (var deflateStream = new DeflateStream(compressedStream, CompressionMode.Decompress))
            {
                int totalRead = 0;
                while (totalRead < decompressed.Length)
                {
                    int read = deflateStream.Read(decompressed, totalRead, decompressed.Length - totalRead);
                    if (read == 0)
                        break;
                    totalRead += read;
                }
            }

            var result = new ApplicationControlProperty.ApplicationTitle[CompressedTitleCount];
            for (int i = 0; i < CompressedTitleCount; i++)
            {
                result[i] = MemoryMarshal.Read<ApplicationControlProperty.ApplicationTitle>(
                    decompressed.AsSpan(i * TitleEntrySize, TitleEntrySize));
            }

            return result;
        }
    }
}