dsdecmp/CSharp/DSDecmp/Formats/Nitro/NitroCFormat.cs

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