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77 lines
2.7 KiB
C#
77 lines
2.7 KiB
C#
using System;
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using System.Collections.Generic;
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using System.Text;
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namespace DSDecmp.Formats.Nitro
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{
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/// <summary>
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/// Base class for Nitro-based decompressors. Uses the 1-byte magic and 3-byte decompression
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/// size format.
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/// </summary>
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public abstract class NitroCFormat : CompressionFormat
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{
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/// <summary>
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/// If true, Nitro Decompressors will not decompress files that have a decompressed
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/// size (plaintext size) larger than MaxPlaintextSize.
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/// </summary>
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public static bool SkipLargePlaintexts = true;
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/// <summary>
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/// The maximum allowed size of the decompressed file (plaintext size) allowed for Nitro
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/// Decompressors. Only used when SkipLargePlaintexts = true.
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/// </summary>
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public static int MaxPlaintextSize = 0x180000;
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/// <summary>
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/// The first byte of every file compressed with the format for this particular
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/// Nitro Dcompressor instance.
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/// </summary>
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protected byte magicByte;
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public NitroCFormat(byte magicByte)
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{
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this.magicByte = magicByte;
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}
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/// <summary>
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/// Converts an array of (at least) 3 bytes into an integer, using the format used
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/// in Nitro compression formats to store the decompressed size.
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/// If the size is not 3, the fourth byte will also be included.
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/// </summary>
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protected int Bytes2Size(byte[] bytes)
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{
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if (bytes.Length == 3)
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return bytes[0] | (bytes[1] << 8) | (bytes[2] << 16);
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else
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return bytes[0] | (bytes[1] << 8) | (bytes[2] << 16) | (bytes[3] << 24);
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}
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public override bool Supports(System.IO.Stream stream)
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{
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long startPosition = stream.Position;
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try
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{
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int firstByte = stream.ReadByte();
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if (firstByte != this.magicByte)
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return false;
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// no need to read the size info as well if it's used anyway.
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if (!SkipLargePlaintexts)
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return true;
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byte[] sizeBytes = new byte[3];
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stream.Read(sizeBytes, 0, 3);
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int outSize = this.Bytes2Size(sizeBytes);
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if (outSize == 0)
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{
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sizeBytes = new byte[4];
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stream.Read(sizeBytes, 0, 4);
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outSize = this.Bytes2Size(sizeBytes);
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}
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return outSize <= MaxPlaintextSize;
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}
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finally
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{
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stream.Position = startPosition;
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}
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}
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}
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}
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