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编程实现算术编码算法中国地质大学计算机学院信息安全专业信息论实验报告实验三算术编码一、实验内容编程实现算术编码算法二、实验环境 1. 计算机 2. Windows 2000 或以上 3. DEVC++ 三、实验目的 1. 进一步熟悉算术编码算法； 2. 掌握 C 语言编程（尤其是数值的进制转换，数值与字符串之间的转换等）四、实验要求 1. 提前预习实验，认真阅读实验原理。 2. 认真高效的完成实验，实验过程中服从实验室管理人员以及实验指导老师的管理。 3. 认真填写实验报告。五、实验原理算术编码是把一个信源表示为实轴上 0 和 1 之间的一个区间，信源集合中的每一个元素都用来缩短这个区间。 1. 算法流程（1）输入信源符号个数，信源概率分布，还有需要编码的符号序列，（2）根据概率可以算出初始编码间隔， High——当前编码的上限， Low——当前编码的下限， high——中间变量，用来计算下一个编码符号的当前间隔的上限， low——中间变量，用来计算下一个编码符号的当前间隔的下限， d——当前间隔之间的距离。（3）扫描需编码的符号序列，确定编码空间第 1 个编码符号的当前间隔为其初始的编码间隔，第 i 个编码符号的当前间隔为第 i-1 个编码后的[Low，High），第 i+1 个编码符号的当前间隔算法如下：high=Low+d*第 i+1 个初始编码符号对应的上限，low=Low+d*第 i+1 个编码符号对应的下限，然后 High=high， Low=low，d=d*第 i 个编码符号的概率。六、参考书 1. 《信息论——基础理论及应用》傅祖芸，电子工业出版社

七、源代码 #include #include #include const double proc[]={0.10,0.10,0.10,0.1,0.1,0.1,0.1,0.1,0.15,0.05}; double result,areaBegin,areaEnd; int cord[1000],cordLength; char str[1000]; int strLength=0; bool readdat() { printf("***********固定模式***********\n"); printf("请输入字符串(0-9):\n"); scanf("%s",str); while(str[strLength]!='\0') strLength++; for(int i=0;i'9'||str[i]<'0') return 1; return 0; } void encord() { printf("编码:"); double w=0.0,len; areaBegin=0.0,areaEnd=1.0; for(int i=0;i

{ temp1*=2; temp2=int(temp1); temp1-=temp2; cord[j]=temp2; printf("%d",temp2); } printf("\n"); } void decord() { printf("译码:\n"); result=0.0; double wei=0.5; for(int i=0;iwei*len) wei+=proc[temp++]; temp--; areaEnd=areaBegin+wei*len;//计算新的空间 areaBegin=areaBegin+(wei-proc[temp]*len); printf("%d",temp); } printf("\n"); int main() { if(readdat()) printf("字符输入错误!!!\n"); else { encord(); decord();

} } return 0; LZ78 算法 #include #include #include #include #define MAXINDEXES 65535 #define MAXBUFFER_IN 256 unsigned int bufin_count,in=0; //in is the pointer to input buffer struct indexes_node{ ////用于构建一级索引的结点 unsigned short indexes[8]; indexes_node* next; void initNode(){ next=NULL; for(int i=0; i<8; i++) indexes[i]=0; } }; struct indexes_node *index_level1[256]={NULL};// storing all ASCII //97 types of chars in a common txtfile(ASCII:32~126 +\n +\t) index_level1[] 为一级索引，以提高查找速度 char* dictionary[MAXINDEXES]={NULL}; //dictionary structure unsigned short p=1; // pointing to an element which is up to be used next time in dictionary[] array char buffer_in[MAXBUFFER_IN]; //input buffer block char ch[2]={'\0'},s[30]={'\0'}; // working memory ch[] stores the current char

in the inputbuffer and s[] stores the current lemma unsigned short tmp_index, index=0; //tmp_index indicates the location of s[] in the dictionary,index is the location of pre-s[] in the dictionary unsigned short find_lemma(char *); //if it finds a matched string,then it returns the index of the string in the array else returns 0 int insert_dictionary(char *); //insert a new lemma into the dictionary and update the index_level1[] array int main(){ FILE *fp_in, *fp_out; char infilename[40]={'\0'},outfilename[40]={'\0'};//the path of a txtfile up to be compressed short len=0; unsigned short sizeofdictionary=0; //只在 fwrite(&sizeofdictionary,1,sizeof(unsigned short),fp_out);用到 while(1){ printf("Please input the path of the txtfile up to be compressed->"); scanf("%s",infilename); if(!(fp_in=fopen(infilename,"r"))){ printf("Can't not find the txtfile!\n"); } else break; } while(1){ printf("Please input the path for the outfile(including outfile name)->"); scanf("%s",outfilename); if(!(fp_out=fopen(outfilename,"wb"))) printf("Memory is not enough!\n"); else break; } fwrite(&sizeofdictionary,1,sizeof(unsigned short),fp_out); while(!feof(fp_in)){ bufin_count=fread(buffer_in,1,MAXBUFFER_IN,fp_in); in=0; while(in

s[len++]=ch[0]; tmp_index=find_lemma(s); //the processor is much too time-consuming if(tmp_index!=0){ //matching index=tmp_index; continue; } // tmp_index==0: no matching insert_dictionary(s); fwrite(&index,1,sizeof(unsigned short),fp_out); fwrite(ch,1,sizeof(char),fp_out); index=0; len=0; for(int k=0;k<30;k++) s[k]='\0'; } } if(index){ //表示能匹配下去但输入缓冲中已无字符了 s[len-1]='\0'; index=find_lemma(s); fwrite(&index,1,sizeof(unsigned short),fp_out); fwrite(ch,1,sizeof(char),fp_out); } rewind(fp_out); fwrite(&p,1,sizeof(unsigned short),fp_out); fclose(fp_out); fclose(fp_in); printf("The LZ78 algorithm has done the compression successfully!\n\n"); scanf("%d",&len); //in order to let the outwindow pause! return 0; } int insert_dictionary(char *lemma){ unsigned short length=strlen(lemma); struct indexes_node *pnext; unsigned short i,j; if(p

dictionary[p][j]='\0'; strcpy(dictionary[p],lemma); p++; } else //字典已满而待压缩数据还没有结束的情况，此时直接输出码字而不插入字典 return -1; //indicating the dictionary is full //TODO: update the index_level1[],find the index i for c i=lemma[0]; if(i<0 || i>255){ printf("Error!\nsome Chinese words or marks in the following txt:\n==================================================\n%s\n",buffer_in); exit(0); } if(index_level1[i]==NULL){ index_level1[i]=(struct indexes_node *)malloc(sizeof(indexes_node)); index_level1[i]->initNode(); index_level1[i]->indexes[0]=p-1; } else { pnext=index_level1[i]; while(pnext->next)pnext=pnext->next; j=0; while(j<8){ if(pnext->indexes[j]==0) break; j++; } } if(j==8){ //the node is full pnext->next=(struct indexes_node *)malloc(sizeof(indexes_node)); pnext->next->initNode(); pnext->next->indexes[0]=p-1; else{ pnext->indexes[j]=p-1; } } } return 1; //insert successfully

unsigned short find_lemma(char * tmp_lemma){ unsigned short length=strlen(tmp_lemma); struct indexes_node *pnext; unsigned short i,j; if(length>0){ i=tmp_lemma[0]; if(i<0 || i>255){ printf("Error!\nsome Chinese words or marks in the following txt:\n===============================================\n%s\n",buffer_in); exit(0); } pnext=index_level1[i]; while(pnext){ j=0; while(j<8){ if(pnext->indexes[j]){ if(strcmp(dictionary[pnext->indexes[j]],tmp_lemma)==0) return pnext->indexes[j]; } else break; j++; pnext=pnext->next; } } } return 0; //not matching }

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