private static int W = 12; // 编码宽度
public static byte[] Compress(string input)
{
BitVirtualSteam bvStream = new BitVirtualSteam();
ThreeTrieST <int> tst = new ThreeTrieST <int>();
for (int i = 0; i < R; i++)
{
tst.Put(((char)i).ToString(), i);
}
int code = R + 1;
while (input.Length > 0)
{
string s = tst.LongestPrefixOf(input);
bvStream.Write(tst.Get(s), 12);
int t = s.Length;
if (t < input.Length && code < L)
{
tst.Put(input.Substring(0, t + 1), code++);
}
input = input.Substring(t);
}
bvStream.Write(R, W);
return(bvStream.GetBytes());
}
public static string Expand(byte[] bytes)
{
BitVirtualSteam bvStream = new BitVirtualSteam(bytes);
string[] st = new string[L];
int i;
for (i = 0; i < R; i++)
{
st[i] = ((char)i).ToString();
}
st[i++] = " ";
int codeword = bvStream.ReadInt(W);
string val = st[codeword];
string output = string.Empty;
// 边解码边增加新码
while (true)
{
output += val;
codeword = bvStream.ReadInt(W);
if (codeword == R)
{
break;
}
string s = st[codeword]; // 下一个编码
if (i == codeword) // 当前的前瞻字符不可用
{
s = val + val[0]; // 由上一个字符串的首字母加该字符串得到的当前字符串
}
if (i < L)
{
st[i++] = val + s[0]; // 编码表新增
}
val = s; //更新编码
}
return(output);
}
