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using System;
using System.IO;
using System.Text;
namespace Tango.AnimatedGif.Decoding
{
internal static class GifHelpers
{
public static string ReadString(Stream stream, int length)
{
byte[] bytes = new byte[length];
stream.ReadAll(bytes, 0, length);
return Encoding.ASCII.GetString(bytes);
}
public static byte[] ReadDataBlocks(Stream stream, bool discard)
{
MemoryStream ms = discard ? null : new MemoryStream();
using (ms)
{
int len;
while ((len = stream.ReadByte()) > 0)
{
byte[] bytes = new byte[len];
stream.ReadAll(bytes, 0, len);
if (ms != null)
ms.Write(bytes, 0, len);
}
if (ms != null)
return ms.ToArray();
return null;
}
}
public static GifColor[] ReadColorTable(Stream stream, int size)
{
int length = 3 * size;
byte[] bytes = new byte[length];
stream.ReadAll(bytes, 0, length);
GifColor[] colorTable = new GifColor[size];
for (int i = 0; i < size; i++)
{
byte r = bytes[3 * i];
byte g = bytes[3 * i + 1];
byte b = bytes[3 * i + 2];
colorTable[i] = new GifColor(r, g, b);
}
return colorTable;
}
public static bool IsNetscapeExtension(GifApplicationExtension ext)
{
return ext.ApplicationIdentifier == "NETSCAPE"
&& Encoding.ASCII.GetString(ext.AuthenticationCode) == "2.0";
}
public static ushort GetRepeatCount(GifApplicationExtension ext)
{
if (ext.Data.Length >= 3)
{
return BitConverter.ToUInt16(ext.Data, 1);
}
return 1;
}
public static Exception UnexpectedEndOfStreamException()
{
return new GifDecoderException("Unexpected end of stream before trailer was encountered");
}
public static Exception UnknownBlockTypeException(int blockId)
{
return new GifDecoderException("Unknown block type: 0x" + blockId.ToString("x2"));
}
public static Exception UnknownExtensionTypeException(int extensionLabel)
{
return new GifDecoderException("Unknown extension type: 0x" + extensionLabel.ToString("x2"));
}
public static Exception InvalidBlockSizeException(string blockName, int expectedBlockSize, int actualBlockSize)
{
return new GifDecoderException(
string.Format(
"Invalid block size for {0}. Expected {1}, but was {2}",
blockName,
expectedBlockSize,
actualBlockSize));
}
public static Exception InvalidSignatureException(string signature)
{
return new GifDecoderException("Invalid file signature: " + signature);
}
public static Exception UnsupportedVersionException(string version)
{
return new GifDecoderException("Unsupported version: " + version);
}
public static void ReadAll(this Stream stream, byte[] buffer, int offset, int count)
{
int totalRead = 0;
while (totalRead < count)
{
totalRead += stream.Read(buffer, offset + totalRead, count - totalRead);
}
}
}
}
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