www.gusucode.com > vc++ 远程控制示例源程序-源码程序 > vc++ 远程控制示例源程序-源码程序\code\PeerYouS\LZWCompress.cpp
//Download by http://www.NewXing.com // LZWCompress.cpp: implementation of the LZWCompress. // ////////////////////////////////////////////////////////////////////// #include "stdafx.h" #include "LZWCompress.h" ///变量定义/////////////////////////////////////////////////////////// int *code_value=NULL; unsigned int *prefix_code=NULL; unsigned char *append_character=NULL; int num_bits=INIT_BITS; unsigned long bytes_in=0,bytes_out=0; unsigned int max_code=0; unsigned long checkpoint=CHECK_TIME; unsigned long incounts=0; unsigned long outcounts=0; unsigned long counts=0; unsigned char *input=NULL,*output=NULL; int output_bit_count=0; unsigned long output_bit_buffer=0; ////////////////////////////////////////////////////////////////////// //进行LZW压缩 unsigned long LZWCompress(unsigned char *inputs,unsigned long lens,unsigned char *outputs) { unsigned int next_code=FIRST_CODE; unsigned int character; unsigned int string_code; unsigned int index; int i, /* All purpose integer */ ratio_new, /* New compression ratio as a percentage */ ratio_old=100; /* Original ratio at 100% */ ///初始化变量 num_bits=INIT_BITS; bytes_in=0;bytes_out=0; max_code=0; checkpoint=CHECK_TIME; incounts=0; outcounts=0; counts=lens; input=inputs; output=outputs; output_bit_count=0; output_bit_buffer=0; max_code = MAXVAL(num_bits); //////////////////////////// for (i=0;i<TABLE_SIZE;i++){ /* Initialize the string table first */ code_value[i]=-1; } string_code=*input++; /* Get the first code */ incounts++; /* This is the main compression loop. Notice when the table is full we try * to increment the code size. Only when num_bits == MAX_BITS and the code * value table is full do we start to monitor the compression ratio. */ while(incounts<counts ) { character=*input++; incounts++; ++bytes_in; index=find_match(string_code,character); if (code_value[index] != -1) string_code=code_value[index]; else { if (next_code <= max_code ) { code_value[index]=next_code++; prefix_code[index]=string_code; append_character[index]=character; } output_code(string_code); /* Send out current code */ string_code=character; if (next_code > max_code) { /* Is table Full? */ if ( num_bits < MAX_BITS) { /* Any more bits? */ max_code = MAXVAL(++num_bits); /* Increment code size then */ } else if (bytes_in > checkpoint) { /* At checkpoint? */ if (num_bits == MAX_BITS ) { ratio_new = bytes_out*100/bytes_in; /* New compression ratio */ if (ratio_new > ratio_old) { /* Has ratio degraded? */ output_code(CLEAR_TABLE); /* YES,flush string table */ num_bits=INIT_BITS; next_code=FIRST_CODE; /* Reset to FIRST_CODE */ max_code = MAXVAL(num_bits); /* Re-Initialize this stuff */ bytes_in = bytes_out = 0; ratio_old=100; /* Reset compression ratio */ for (i=0;i<TABLE_SIZE;i++) /* Reset code value array */ code_value[i]=-1; } else /* NO, then save new */ ratio_old = ratio_new; /* compression ratio */ } checkpoint = bytes_in + CHECK_TIME; /* Set new checkpoint */ } } } } output_code(string_code); /* Output the last code */ if (next_code == max_code) { /* Handles special case for bit */ ++num_bits; /* increment on EOF */ } output_code(TERMINATOR); /* Output the end of buffer code */ output_code(0); /* Flush the output buffer */ output_code(0); output_code(0); return outcounts; } //匹配表中数据 int find_match(unsigned int hash_prefix, unsigned int hash_character) { int index, offset; index = (hash_character << HASHING_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_prefix && append_character[index] == hash_character) return(index); index -= offset; if (index < 0) index += TABLE_SIZE; } } //输出编码 void output_code(unsigned int code) { output_bit_buffer |= (unsigned long) code << (32 - num_bits - output_bit_count); output_bit_count += num_bits; while (output_bit_count >= 8) { *output++=(unsigned char)(output_bit_buffer >> 24); output_bit_buffer <<= 8; output_bit_count -= 8; bytes_out++; /* ADDED for compression monitoring */ outcounts++; } } //为各表分配内存空间 bool LZWAllocTables() { bool flag=true; __try{ code_value=(int*)GlobalAlloc(GPTR,TABLE_SIZE*sizeof(unsigned int)); prefix_code=(unsigned int *)GlobalAlloc(GPTR,TABLE_SIZE*sizeof(unsigned int)); append_character=(unsigned char*)GlobalAlloc(GPTR,TABLE_SIZE*sizeof(unsigned char)); } __except(EXCEPTION_EXECUTE_HANDLER){ if(code_value) code_value=(int*)GlobalFree(code_value); if(prefix_code) prefix_code=(unsigned int*)GlobalFree(prefix_code); if(append_character) append_character=(unsigned char*)GlobalFree(append_character); flag=false; } return flag; } //释放各表所占用的内存 void LZWFreeTables() { if(code_value) code_value=(int*)GlobalFree(code_value); if(prefix_code) prefix_code=(unsigned int*)GlobalFree(prefix_code); if(append_character) append_character=(unsigned char*)GlobalFree(append_character); }