void Zlib::Compress()
{
	Begin();
	if(deflateInit2(&z, compression_level, Z_DEFLATED,
	                hdr && !gzip ? MAX_WBITS : -MAX_WBITS, DEF_MEM_LEVEL,
	                Z_DEFAULT_STRATEGY) != Z_OK)
		Panic("deflateInit2 failed");
	mode = DEFLATE;
	if(gzip)
		WhenOut(sGZip_header, 10);
}