Citation Gailly, J. The zlib data format is itself portable across platforms. Unlike the LZW compression method used in Unix compress 1 and in the GIF image format, the compression method currently used in zlib essentially never expands the data. LZW can double or triple the file size in extreme cases. A more precise, technical discussion of both points is available on another page.
For now this page is mainly a pointer to zlib itself and to the official zlib and deflate documentation. Note that the specifications both achieved official Internet RFC status in May , and zlib itself was adopted by JavaSoft in version 1. Active 10 months ago. Viewed k times.
Improve this question. Francisco Corrales Morales 3, 1 1 gold badge 34 34 silver badges 61 61 bronze badges. Abhishek Jain Abhishek Jain 8, 5 5 gold badges 19 19 silver badges 36 36 bronze badges. Add a comment. Active Oldest Votes. Short form:. All of the mentioned patents have since expired. Improve this answer. Community Bot 1 1 1 silver badge. Mark Adler Mark Adler This post is packed with so much history and information that I feel like some citations need be added incase people try to reference this post as an information source.
Though if this information is reflected somewhere with citations like Wikipedia, a link to such similar cited work would be appreciated. I am the reference, having been part of all of that. This post could be cited in Wikipedia as an original source. FYI: Mark Adler is an American software engineer, and has been heavily involved in space exploration. He is best known for his work in the field of data compression as the author of the Adler checksum function, and a co-author of the zlib compression library and gzip.
When you see. Second, tar preserves all of the Unix directory information, whereas zip was not designed to do that. Later extensions to the zip format with Unix-specific extra blocks tries to remedy this problem. You seem to be confusing formats with implementation. Show 26 more comments. Niels Keurentjes Niels Keurentjes Konrad Rudolph k gold badges silver badges bronze badges.
Tim Zimmermann Tim Zimmermann 5, 3 3 gold badges 26 26 silver badges 35 35 bronze badges. You are overstating the point. If people wanted random-access compressed archives, they could create ". They don't, because most people aren't that interested in random access. There is a big community around the. You use this format every time you look at a webpage in the Internet Archive Wayback Machine. You need to go through all the entries from the beginning to get the one specific entry wanted, even worse: you need to go through all the entries until the end because the same file may be archived several times in several versions on several places in the same archive - and there is no means to figure it out except to read the whole archive entry by entry.
The Overflow Blog. Podcast Explaining the semiconductor shortage, and how it might end. Does ES6 make JavaScript frameworks obsolete? The default value matches the largest window size.
It also asks for the inclusion of the header and trailer of the compressed file. The possible values are:. The initial value of the buffer size is indicated in the bufsize argument. However, the important aspect about this parameter is that it doesn't need to be exact, because if extra buffer size is needed, it will automatically be increased.
The following example shows how to decompress the string of data compressed in our previous example:. Decompressing big data streams may require memory management due to the size or source of your data. It's possible that you may not be able to use all of the available memory for this task or you don't have enough memory , so the decompressobj method allows you to divide up a stream of data in to several chunks which you can decompress separately. This function returns a decompression object, which what you use to decompress the individual data.
The wbits argument has the same characteristics as in decompress function previously explained. The following code shows how to decompress a big stream of data that is stored in a file. Firstly, the program creates a file named "outfile. This ensures the creation of a header and a trailer in the data. The file is then decompressed using chunks of data. Again, in this example the file doesn't contain a massive amount of data, but nevertheless, it serves the purpose of explaining the buffer concept.
The compressed data contained in a file can be easily decompressed, as you've seen in previous examples. This example is very similar to the previous one in that we're decompressing data that originates from a file, except that in this case we're going back to using the one-off decompress method, which decompresses the data in a single method call.
This is useful for when your data is small enough to easily fit in memory. The above program opens the file "compressed. As the file contains a small amount of data, the example uses the decompress function. However, as the previous example shows, we could also decompress the data using the decompressobj function. The Python library zlib provides us with a useful set of functions for file compression using the zlib format.
The functions compress and decompress are normally used. These functions help split the data into smaller and more manageable chunks, which can be compressed or decompressed using the compress and decompress functions respectively. Keep in mind that the zlib library also has quite a few more features than what we were able to cover in this article.
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