/// <summary>
/// 通过一个文件流创建哈夫曼解码器
/// </summary>
/// <param name="f"></param>
public HuffmanDecoder(FileStream f)
{
source = f;
Int32 i;
byte[] buffer = new byte[4];
f.Read(buffer, 0, 4); //读取文件头标记,获取编码表的长度
i = Codec.ReadInt(buffer, 4);
buffer = new byte[i]; //读取文件头中编码表
f.Read(buffer, 0, i);
codex = new HuffmanCodex(buffer); //反序列化哈夫曼编码
}
public static double AverageCodeLength(Analyzer a, HuffmanCodex c)
{
long length = 0;
long sum = 0;
foreach (int i in a.Value.Values)
{
sum += i;
}
foreach (Block i in c.Codex.Keys)
{
length += c.Codex[i].length * a.Value[i];
}
return(1.0 * length / sum);
}
/// <summary>
/// 点击压缩
/// </summary>
private void Compress_Click(object sender, EventArgs e)
{
FileStream fs = File.OpenRead(InputFile.Text);
try
{
StatusInfo.Clear();
Compress.Enabled = false;
StatusText = "分析文件......";
StatusText = "加载哈夫曼编码编码......";
Codex.Analyzer a = new Codex.Analyzer(fs);
Codex.HuffmanCodex h = new Codex.HuffmanCodex(a);
StatusText = "写入哈夫曼编码......";
fs.Position = 0;
Codex.HuffmanEncoder en = new Codex.HuffmanEncoder(h, fs);
FileStream target = File.OpenWrite(OutputFile.Text);
target.SetLength(0);
target.WriteByte((Byte)Codex.Block.BlockSize); //文件第一位写块大小
en.WriteCodexToStream(target);
StatusText = "写入压缩文件......";
var buffer = en.ReadToEnd();
target.Write(buffer, 0, buffer.Length);
StatusText = "写入完成.";
StatusText = "压缩率:" + (100.0 * target.Length / fs.Length) + '%';
StatusText = "平均编码长度:" + Codex.Debug.AverageCodeLength(a, h) + "位";
StatusText = "字典大小:" + Codex.Block.BlockSize + "字节";
StatusText = "压缩文件头长度:" + h.Length + "字节";
target.Close();
}
catch (DataMisalignedException)
{
MessageBox.Show("文件长度不能够均分到每个块中", "错误", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
fs.Close();
Compress.Enabled = true;
}
/// <summary>
/// 通过已生成的哈夫曼编码和要编码的数据流创建编码器
/// </summary>
/// <param name="codex">哈夫曼编码表</param>
/// <param name="s">要编码的字符流</param>
public HuffmanEncoder(HuffmanCodex codex, Stream s)
{
this.codex = codex;
this.source = s;
}