用C++实现数据无损压缩、解压（使用LZW算法） - 图文

for(i = 0; i < 256; i ++) {

StrTable[i].string = (char *)realloc(StrTable[i].string, 1); StrTable[i].string[0] = i; StrTable[i].len = 1; }

StrTable[256].string = NULL; StrTable[256].len = 0; StrTable[257].string = NULL; StrTable[257].len = 0; ItemPt = 257; Bits = 9; }

void LZWCoder::CopyStr(TStr *d, TStr s) {

unsigned int i;

d->string = (char *)realloc(d->string, s.len); for(i = 0; i < s.len; i ++)

d->string[i] = s.string[i]; d->len = s.len; }

void LZWCoder::StrJoinChar(TStr *s, char c) {

s->string = (char *)realloc(s->string, s->len + 1); s->string[s->len ++] = c; }

unsigned int LZWCoder::InStrTable(TStr s) {

unsigned int i,j; bool b;

for(i = 0; i <= ItemPt; i ++) {

if(StrTable[i].len == s.len)

{

b = true;

for(j = 0; j < s.len; j ++)

if(StrTable[i].string[j] != s.string[j]) {

b = false; break; } if(b) return i; } }

return 65535; }

void LZWCoder::AddTableEntry(TStr s) {

CopyStr(&StrTable[++ItemPt], s); }

void LZWCoder::WriteCode(char *dest, unsigned int b) {

unsigned char i;

for(i = 0; i < Bits; i++) {

Bit[BitPt ++] = (b & (1 << (Bits - i - 1))) != 0; if(BitPt == 8) {

BitPt = 0;

dest[BytePt ++] = (Bit[0] << 7) + (Bit[1] << 6) + (Bit[2] << 5) + (Bit[3] << 4) + (Bit[4] << 3) + (Bit[5] << 2) + (Bit[6] << 1) + Bit[7];

} } }

unsigned int LZWCoder::GetNextCode(char *src) {

unsigned char i; unsigned int c = 0;

for(i = 0; i < Bits; i ++) {

c = (c << 1) + ((src[BytePt] & (1 << (8 - (BitPt ++) - 1))) != 0); if(BitPt == 8) {

BitPt = 0; BytePt ++; } }

return c; }

void LZWCoder::StrFromCode(TStr *s, unsigned int c) {

CopyStr(s, StrTable[c]); }

void LZWCoder::WriteString(char *dest, TStr s) {

unsigned int i;

for(i = 0; i < s.len; i++)

dest[OutBytes ++] = s.string[i]; }

unsigned int LZWCoder::Encode(char *src, unsigned int len, char *dest) {

TStr Omega, t; char k;

unsigned int i; unsigned int p; BytePt = 0; BitPt = 0; InitStrTable(); WriteCode(dest, 256); Omega.string = NULL; Omega.len = 0; t.string = NULL; t.len = 0;

for(i = 0; i < len; i ++) {

k = src[i];

CopyStr(&t, Omega); StrJoinChar(&t, k);

if(InStrTable(t) != 65535) CopyStr(&Omega, t); else {

WriteCode(dest, InStrTable(Omega)); AddTableEntry(t); switch(ItemPt) {

case 512: Bits = 10; break; case 1024: Bits = 11; break; case 2048: Bits = 12; break;

case 4096: WriteCode(dest, 256); InitStrTable(); }

Omega.string = (char *)realloc(Omega.string, 1); Omega.string[0] = k; Omega.len = 1; } }

WriteCode(dest, InStrTable(Omega)); WriteCode(dest, 257); Bits = 7;