Inflate动态Huffman解压缩-编程知识

Inflate动态Huffman解压缩

上个已经实现GZIP压缩文件格式的Inflate静态Huffman解压，这个实现Inflate的无压缩输出和动态Huffman解压。

Java语言实现，Eclipse下编写。

范式Huffman解码实现，输入huffman编码，输出原始数据

    // 范式huffman解码static class CanonicalCode {Vector<Node> table = new Vector<>();public CanonicalCode(int[] len) {for (int i=0; i<len.length; i++)if (len[i] != 0) // 过滤0-即不使用的节点table.add( new Node(i, len[i]) ); // value, bits Length (值, 待编码的编码长度)// 按编码长度+值排序Collections.sort(table, new Comparator<>() {@Overridepublic int compare(Node o1, Node o2) {return o1.bitLen!=o2.bitLen ? o1.bitLen-o2.bitLen : o1.value - o2.value;}});// 初始化第一个节点，实现规则1table.get(0).code = 1 << table.get(0).bitLen;// 计算每一个值得huffman编码for (int i=1; i<table.size(); i++) {Node node = table.get(i);Node prev = table.get(i-1);if (node.bitLen == prev.bitLen)  // 如果位长相等+1，实现规则2node.code = prev.code + 1;else if (node.bitLen > prev.bitLen)	// 位长不等，实现规则3node.code = ( prev.code + 1) << (node.bitLen - prev.bitLen);  // 左移'位长差'}}// 打印符号和huffman码的对应关系void debug() {for (int i=0; i<table.size(); i++) {Node n = table.get(i);System.out.println( n);}}// 根据传入的huffman编码，得到原始数值Integer findValue(int code) {for (Node node : table)if (node.code == code)return node.value;return null;}}

无压缩数据解码：

	bis.alignByte(); // 对齐字节边界int len = bis.ReadBits(16);int nlen = bis.ReadBits(16);assert len + nlen == 65535;for (int i=0; i<len; i++) {baos.Write(bis.ReadBits(8));}

动态huffman解码：

	else if (bType == 2) { // dynamic huffman// length有29个int hlit = bis.ReadBits(5);  // CL1数量 - 字/长度 码个数, LIT(literal/length)// distance码有30个int hdist = bis.ReadBits(5); // CL2数量 - 距离 码个数, DIST(distance)int hclen = bis.ReadBits(4); // c_len:code lengths for the code lengthint cl1_num = hlit + 257;  // CL1(Code Length 1): 'literal/length' length (literal[0..255]+压缩块结束[256] = 257)int cl2_num = hdist + 1;   // CL2(Code Length 2): 'distance code' lengthint ccl_num = hclen + 4;   // int[] cl1 = new int[cl1_num];int[] cl2 = new int[cl2_num];int[] ccl = new int[19]; // ccl bits// 读取CCLArrays.fill(ccl, 0);int[] PermutationtTable = new int[] {16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15 };for (int i=0; i<ccl_num; i++) { // 读取CCL, 每个3bitint p = PermutationtTable[i];ccl[p] = bis.ReadBits(3);}// 通过CCL构建范式huffman编码CanonicalCode codes = new CanonicalCode(ccl);//读取CL1和CL2,'literal/length' Sequence 码流 + dist流IntBuffer sq = IntBuffer.allocate(cl1_num + cl2_num);int prevValue = -1, cl_decode_num = 0;while (cl_decode_num < cl1_num + cl2_num) {Integer value = null;int code = 1;// 范式huffman解码int bits = 1;while (value == null) {code = (code << 1 ) | bis.ReadBit();  // huffman编码value = codes.findValue( code); // 查找对应的符号if ( (bits++) > 15 )throw new java.lang.IllegalArgumentException();}// 处理value， 实现 0-15，16，17，18 这套规则int[] bs;if (value == 17) { // 标识长度int len = bis.ReadBits(3) + 3;bs = new int[len];Arrays.fill(bs, (byte)0);}else if (value == 18) {int len = bis.ReadBits(7) + 11;bs = new int[len];Arrays.fill(bs, (byte)0);}else if (value == 16) {int len = bis.ReadBits(2) + 3;bs = new int[len];Arrays.fill(bs, (byte) prevValue);}else if (value >=0 && value <= 15){bs = new int[] {  value };prevValue = value;}else throw new java.lang.IllegalArgumentException(value + "");sq.put(bs); // 写入符号cl_decode_num += bs.length; // 增加已得到的码流长度}int[] bs = sq.array();// 分别得到CL1和CL2 System.arraycopy(bs, 0, cl1, 0, cl1.length);System.arraycopy(bs, cl1.length, cl2, 0, cl2.length);CanonicalCode code1 = new CanonicalCode(cl1); // literal/length解码器CanonicalCode code2 = new CanonicalCode(cl2); // distance解码器// 解码Integer value = null;do {// 解literal/length码int code = 1;do {code = (code << 1) | bis.ReadBit(); // 读取Huffman codevalue = code1.findValue(code);} while (value == null);// 判断if (value >= 0 && value <= 255)// literalbaos.Write(value);else if (value == 256) // 结束标志break ;else if (value >= 257 && value <= 285) { // length// 处理长度int length = LengthExtraCodeLengthsTable.get(value);int bits = LengthExtraCodeBitsTable.get(value); // 扩展bit长if (bits != 0) {int ext =  ReadExtCode(bis, bits);length = length + ext;}// 读取huffman编码code = 1;do {code = (code << 1) | bis.ReadBit(); // 读取Huffman codevalue = code2.findValue(code);} while (value == null);// 处理距离int distance = DistanceExtraCodeLengthsTable.get(value);bits = DistanceExtraCodeBitsTable.get(value); // 距离扩展if (bits != 0) {int ext =ReadExtCode(bis , bits);distance = distance + ext;}// LZ77滑动窗口计算获取量int[] arr = baos.GetInts();int d = arr.length - distance;if (d < 0) {d = 0;length = length + distance - arr.length;}// 读取滑动窗口，写入到结果for (int i=0; i<length; i++) {int m = arr[ d + i];baos.Write(m);arr = baos.GetInts();}}} while (value != 256);}

输出结果：