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// 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);
}