Higher occuring characters simply have shorter codes and less occuring characters longer codes, which most of the time results in smaller total amount of bits. This implementation operates on individual characters, it does not encode sections of text which would give better compression results. How does the decompressor know how many bits are representing the code's length? In the beginning of the file, the first two bytes indicate exactly that. Informations about each characters are not written at the beginning or the end of the file, but directly whenever the character is in the text the only information written directly at the beginning of the file - even before the redundant zeros - is a two-bit indicator of in how many bits the codes lengths are stored.
The bits are stored in bytes, and each byte has 8 bits. If the amount of bits isn't divisible by 8 without a remainder, additional bits must be added. This implementation adds zeros at the beginning of the compressed text, and because the first information on each character is if it has 0 or has not 1 already been encountered, then the first bit on the first character must obviously always be 1.
The only information added to a character that was already encountered is one bit 0 , which indicates that it has already been encountered. Decompressor then starts reading from the first bit and gradually adds next, until it finds a match in whenever it stores already encountered codes and their latin-2 representations.
Storing each bit while compressing and mainly decompressing as one character was an absolutely retarded idea. Yes, to be perfectly clear we are indeed talking about stuffing exabytes of data into kilobytes.
To understand how it works, we have to take a little detour to see how data compression works WinZip, WinRAR, 7-zip etc. Compression is a reduction in the number of bits needed to represent data. Consider the following string:. The above string is 18 characters long. Notice that the substring aaa can be found a lot of times. We take the longest common sequences in data and try to represent them using as few bits as possible.
Now, compressing this string means we have to represent this information in less than 18 characters. Instead of using the string directly, we use an intermediate compressed form of the string along with some instructions on how to get the original string:.
Compression just happened. The real takeaway is that compression thrives when the data has some repeating patterns i.
As an example, when compressing text we can use the knowledge that the letter e is the most common letter in modern English. No discussion on zip bombs is complete without the infamous It is a zip file consisting of 42 kilobytes of compressed data, containing five layers of nested zip files in sets of 16, each bottom layer archive containing a 4. The The principal of zip bombs extends to many other areas. Basically it crashes a web browser by causing the XML parser to run out of memory.
Most web browsers today defend against this by capping the memory allocated to the parser. We are going to build an exabyte zip bomb. Say you make an initial text file around 10MB worth of zeros. Save it and close your text editor. Go to the folder where your text file is stored, make around ten copies of the text file in the same folder. Now open up a command prompt where your text file is stored and type:.
What this does is combine all the copies of the text files into one. Better still, it can do this quickly without any lag. Text editors freeze up because of having to deal with the user interface. Using the command line, everything happens as a background process without a hiccup. Combining ten files of 10MB will yield one MB file, combine ten copies of that and you have a 1GB text file full of zeros in just a few seconds.
Lines creates a FileStream object which points to the compressed text file. We provide FileMode. Open and FileAccess. Read values in the constructor because we are simply reading the contents of the file.
Line 8 creates a GZipStream object. The only difference here, as you can see, is the second argument which specifies the compression mode. We provide the CompressionMode. Decompress value. This value is used to decompress the compressed data of the stream. We passed the created GZipStream object to the StreamReader object in line 10 which is the one who will read the contents of the file.
Line 11 uses the ReadToEnd method which decompresses the content of the compressed file and returns the content as a string. The uncompressed content is then displayed in line If you compressed your file using the DeflateStream class, then you must use the same class for decompressing it.
Example 5 shows you how to use the DeflateStream class to decompress a file. It is just similar to using the GZipStream class. This lesson only shows you how to compress a simple text file. You can use the classes we discussed here on various types of files. Home Top Menu. Home C.
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