ItsTheSky
d6d621dc92
- Created project.nuget.cache to store NuGet package cache information. - Added project.packagespec.json to define project restore settings and dependencies. - Included rider.project.restore.info for Rider IDE integration.
89 lines
3.3 KiB
C#
89 lines
3.3 KiB
C#
using System.IO.Compression;
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namespace GsaEditor.Core.Compression;
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/// <summary>
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/// Provides zlib compression and decompression utilities for GSA archive entries.
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/// The GSA format stores zlib-wrapped data: 2-byte header (CMF+FLG) + deflate stream + 4-byte Adler-32 checksum.
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/// This helper skips the 2-byte zlib header and uses <see cref="DeflateStream"/> for the core deflate data.
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/// </summary>
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public static class ZlibHelper
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{
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/// <summary>
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/// Decompresses zlib-wrapped data into a byte array of the specified original size.
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/// Skips the 2-byte zlib header before feeding data to <see cref="DeflateStream"/>.
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/// </summary>
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/// <param name="compressedData">The zlib-wrapped compressed data (header + deflate + checksum).</param>
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/// <param name="originalLength">The expected decompressed size in bytes.</param>
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/// <returns>The decompressed byte array.</returns>
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/// <exception cref="InvalidDataException">Thrown when decompression fails or data is corrupt.</exception>
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public static byte[] Decompress(byte[] compressedData, uint originalLength)
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{
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if (compressedData.Length < 2)
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throw new InvalidDataException("Compressed data is too short to contain a zlib header.");
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// Skip the 2-byte zlib header (typically 0x78 0x9C for default compression)
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using var ms = new MemoryStream(compressedData, 2, compressedData.Length - 2);
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using var deflate = new DeflateStream(ms, CompressionMode.Decompress);
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var result = new byte[originalLength];
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int totalRead = 0;
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while (totalRead < result.Length)
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{
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int bytesRead = deflate.Read(result, totalRead, result.Length - totalRead);
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if (bytesRead == 0)
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break;
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totalRead += bytesRead;
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}
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return result;
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}
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/// <summary>
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/// Compresses data using zlib format: 2-byte header + deflate stream + 4-byte Adler-32 checksum.
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/// </summary>
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/// <param name="data">The uncompressed data to compress.</param>
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/// <returns>The zlib-wrapped compressed byte array.</returns>
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public static byte[] Compress(byte[] data)
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{
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using var output = new MemoryStream();
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// Write zlib header: CMF=0x78 (deflate method, 32K window), FLG=0x9C (default level, valid check bits)
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output.WriteByte(0x78);
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output.WriteByte(0x9C);
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using (var deflate = new DeflateStream(output, CompressionLevel.Optimal, leaveOpen: true))
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{
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deflate.Write(data, 0, data.Length);
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}
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// Write Adler-32 checksum in big-endian byte order
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uint adler = ComputeAdler32(data);
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output.WriteByte((byte)(adler >> 24));
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output.WriteByte((byte)(adler >> 16));
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output.WriteByte((byte)(adler >> 8));
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output.WriteByte((byte)adler);
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return output.ToArray();
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}
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/// <summary>
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/// Computes the Adler-32 checksum of the given data.
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/// </summary>
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/// <param name="data">The data to checksum.</param>
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/// <returns>The 32-bit Adler-32 checksum value.</returns>
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private static uint ComputeAdler32(byte[] data)
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{
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const uint MOD_ADLER = 65521;
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uint a = 1, b = 0;
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for (int i = 0; i < data.Length; i++)
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{
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a = (a + data[i]) % MOD_ADLER;
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b = (b + a) % MOD_ADLER;
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}
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return (b << 16) | a;
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}
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}
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