实验三LZW编码.doc

实验三 LZW编码 一、实验目的 1、加深对LZW编码的理解； 2、掌握LZW编码的程序设计。 二、原理与说明 LZW编码的步骤： 串表 a 1 aab 7 b 2 bc 8 c 3 cb 9 aa 4 baa 10 ab 5 aaba 11 ba 6 abb 12 a a b aa b c ba aab ab bc 1 1 2 4 2 3 6 7 5 8 三、 计算机 程序如下：#includestdio.h #includeconio.h #includemalloc.h #includestring.h #includeprocess.h #define BIRS 12 #define HASHING_SHIFT BITS-8 #define MAX_VALUE(1BITS)-1 #define MAX_CODE MAX_VALUE-1 #if BITS==14 #define TABLE_SIZE 18041 #endif #if BITS==13 #define TABLE_SIZE 9029 #endif #if BITS=12 #define TABLE_SIZE 5021 int *code_value; unsigned int *prefix_code; unsigned char *append_character; unsigned char decode_stack[4000]; char ok; find match(int hash_perfix,unsigned int hash_character) { int index; int offset; index=(hash_characterHASHING_SHIFT)^hash_prefix; if(index==0) offset=1; else offset=TABLE_SIZE-index; while(1) { if(code_value[index]==-1) return(index); if(prefix_code[index]==hash_prefixappend_character[index]==hash_character) return(index); index-=offset; if(index0) index+=TABLE_SIZE; } } input_code(FILE*input) { unsigned int return_value; static int input_bit_count=0; static unsigned long input_bit_buffer=0L; while(input_bit_count=24) { input_bit_buffer|=(unsigned long)getc(input)(24-input_bit_count); input_bit_count+=8; } return_value=input_bit_buffer(32-BITS); input_bit_buffer=BITS; input_bit_count-=BITS; return(return_value); } void output_code(FILE*output,unsigned int code) { static int output_bit_count=0; static unsigned long output_bit_buffer=0L; output_bit_buffer|=(unsigned long)code(32-BITS-output_bit_count); output_bit_count+=BITS; while(output_bit_count=8) { putc(output_bit_buffer24,output); output_bit_buffer=8; output_bit_count-=8; } } void compress(FILE *input,FILE *output) { unsigned int next_code; unsigned int character; unsigned int string_code; unsigned int index; int i; next_code=256; for(i=0;iTABLE_SIZE;i++) code_value[i]=-1; i=0; printf(\n\nCompressing..