CRC校验实验报告

1、实验三 CRC校验一、CRC校验码的基本原理编码过程：CRC校验码的编码方法是用待发送的二进制数据t(x)除以生成多项式g(x)，将最后的余数作为CRC校验码。其实现步骤如下： 1 设待发送的数据块是m位的二进制多项式t(x)，生成多项式 为r阶的g(x)。在数据块的末尾添加r个0，数据块的长度增 加到m+r位。 2 用生成多项式g（x）去除 ，求得余数为阶数为r-1的二进制 多项式y(x)。此二进制多项式y(x)就是t(x)经过生成多项式 g(x)编码的CRC校验码。 3 将y(x)的尾部加上校验码，得到二进制多项式 。 就是包含 了CRC校验码的待发送字符串。解码过程： 从CRC的编码规则

2、可以看出，CRC编码实际上是将代发送的m位二进制多项式t(x)转换成了可以被g(x)除尽的m+r位二进制多项式所以解码时可以用接收到的数据去除g（x），如果余数位零，则表示传输过程没有错误；如果余数不为零，则在传输过程中肯定存在错误。许多CRC的硬件解码电路就是按这种方式进行检错的。同时,可以看做是由t（x）和CRC校验码的组合，所以解码时将接收到的二进制数据去掉尾部的r位数据，得到的就是原始数据。解码过程示例：运行结果：附录（实现代码）：using System;using System.Collections.Generic;using System.Text;namespace CRC

3、public abstract class Change / <summary> / 字节数组转进制 / </summary> / <param name="bytes">字节数组</param> / <param name="b1">字节数组长度</param> public static string ByteToHex(byte bytes, int b1) string returnStr = "" if (bytes != null) for (int

4、i = 0; i < b1; i+) returnStr += bytesi.ToString("x2").ToUpper(); return returnStr; / <summary> / 16进制转字节数组 / </summary> / <param name="hexStr">16进制数</param> public static byte HexToByte(string hexStr) hexStr = hexStr.Replace(" ", "")

5、; if (hexStr.Length % 2) != 0) hexStr += " "/空格 byte bytes = new bytehexStr.Length / 2; for (int i = 0; i < bytes.Length; i+) bytesi = Convert.ToByte(hexStr.Substring(i * 2, 2), 16); return bytes; / <summary> / 字符串转进制 / </summary> / <param name="str">字符串</

6、param> / <returns></returns> public static string StrToHex(string str) if (str = "") return "" byte bTemp = System.Text.Encoding.Default.GetBytes(str); return ByteToHex(bTemp, bTemp.Length); / <summary> / 16进制转字符串 / </summary> / <param name="str

7、">16进制</param> / <returns></returns> public static string HexToStr(string str) byte bytes = new bytestr.Length; bytes = HexToByte(str); return Encoding.Default.GetString(bytes); namespace CRC /哈夫曼树 150 / 结点类Node的定义如下： public class Node private int weight; /结点权值 private int

8、lChild; /左孩子结点 private int rChild; /右孩子结点 private int parent; /父结点 /结点权值属性 public int Weight get return weight; set weight = value; /左孩子结点属性 public int LChild get return lChild; set lChild = value; /右孩子结点属性 public int RChild get return rChild; set rChild = value; /父结点属性 public int Parent get return

9、parent; set parent = value; /构造器 public Node() weight = 0;lChild = -1; rChild = -1; parent = -1; /构造器 public Node(int w, int lc, int rc, int p) weight = w; lChild = lc; rChild = rc; parent = p; public class HuffmanTree private List<Node> data = new List<Node>(); /结点数组 private int leafNum

10、; /叶子结点数目 /索引器 public Node thisint index get return dataindex; set dataindex = value; /叶子结点数目属性public int LeafNum public int LeafNum get return leafNum; set leafNum = value; /构造器 public HuffmanTree() public HuffmanTree(List<NumKindchar> m_NumKind) leafNum = m_NumKind.Count; for (int j = 0; j &

11、lt; 2 * m_NumKind.Count - 1; j+)/n中字符共需要2n-1个节点 Node databuff = new Node(); if (j < this.leafNum) databuff.Weight = m_NumKindj.num; data.Add(databuff);/每创建一个节点将节点加入节点数组data当中 public List<Node> Create() int max1, max2, tmp1, tmp2; /处理n个叶子结点，建立哈夫曼树 for (int i = 0; i < this.leafNum - 1; +i)

12、 max1 = max2 = Int32.MaxValue; tmp1 = tmp2 = 0; /在全部结点中找权值最小的两个结点 for (int j = 0; j < this.leafNum + i; +j) if (dataj.Weight < max1) && (dataj.Parent = -1) max2 = max1; tmp2 = tmp1; tmp1 = j; max1 = dataj.Weight; else if (dataj.Weight < max2) && (dataj.Parent = -1) max2 = dataj.Weight; tmp2 = j; datatmp1.Parent = this.leafNum + i; datatmp2.Parent = this.leafNum + i; datathis.leafNum + i.Weight = datatmp1.Weight + datatmp2.Weight; datathis.leafNum + i.LChild = tmp1; datathis.leafNum + i.RChild = tmp2; return data; public class NumKindchar public char let