如何解决C ++使用std :: fstream解码LZ77压缩数据太慢
我的代码中有一个函数,可以解码使用LZ77算法压缩的文件。但是在15 MB的输入文件上,解压缩大约需要3分钟(太慢)。表现不佳的原因是什么?在循环的每一步中,我读取两个或三个字节,并获取长度,偏移量和下一个字符。如果offset不为零,我还必须将“ offset”字节移回输出流并读取“ length”字节。然后,我将它们插入相同流的末尾,然后在此处写入下一个字符。
void uncompressData(long block_size,unsigned char* data,fstream &file_out)
{
unsigned char* append;
append = new unsigned char[buf_length];
link myLink;
long cur_position = 0;
file_out.seekg(0,ios::beg);
cout << file_out.tellg() << endl;
int i=0;
myLink.length=-1;
while(i<(block_size-1))
{
if(myLink.length!=-1) file_out << myLink.next;
myLink.length = (short)(data[i] >> 4);
//cout << myLink.length << endl;
if(myLink.length!=0)
{
myLink.offset = (short)(data[i] & 0xF);
myLink.offset = myLink.offset << 8;
myLink.offset = myLink.offset | (short)data[i+1];
myLink.next = (unsigned char)data[i+2];
cur_position=file_out.tellg();
file_out.seekg(-myLink.offset,ios_base::cur);
if(myLink.length<=myLink.offset)
{
file_out.read((char*)append,myLink.length);
}
else
{
file_out.read((char*)append,myLink.offset);
int k=myLink.offset,j=0;
while(k<myLink.length)
{
append[k]=append[j];
j++;
if(j==myLink.offset) j=0;
k++;
}
}
file_out.seekg(cur_position);
file_out.write((char*)append,myLink.length);
i++;
}
else {
myLink.offset = 0;
myLink.next = (unsigned char)data[i+1];
}
i=i+2;
}
unsigned char hasOddSymbol = data[block_size-1];
if(hasOddSymbol==0x0) { file_out << myLink.next; }
delete[] append;
}
解决方法
您可以尝试在内存中的std::stringstream
上执行此操作:
#include <sstream>
void uncompressData(long block_size,unsigned char* data,fstream& out)
{
std::stringstream file_out; // first line in the function
// the rest of your function goes here
out << file_out.rdbuf(); // last line in the function
}
版权声明:本文内容由互联网用户自发贡献,该文观点与技术仅代表作者本人。本站仅提供信息存储空间服务,不拥有所有权,不承担相关法律责任。如发现本站有涉嫌侵权/违法违规的内容, 请发送邮件至 dio@foxmail.com 举报,一经查实,本站将立刻删除。