zlib is designed to be a free, general-purpose, legally unencumbered, lossless data-compression library for use on virtually any computer hardware and operating system. The zlib data format is portable across platforms.

Unlike the LZW compression method used in Unix compress, the compression method currently used in zlib essentially never expands the data. (LZW can double or triple the file size in extreme cases.) zlib's memory footprint is also independent of the input data and can be reduced, if necessary, at some cost in compression.

Here are some key features of "zlib":

- inflate is about 20% faster and minimizes memory allocation
- crc32 is about 50% faster
- New, improved, and supported DLL interface and DLL FAQ
- New functions and functionality:
- deflate() and inflate() will now optionally encode and decode gzip streams
- raw deflate() and inflate() now documented and supported
- New inflateBack() functions for call-back interface -- faster than inflate()
- Z_BLOCK flush option and new return information added to inflate to facilitate appending to deflate streams
- raw deflate() now accepts a dictionary -- for appending
- deflatePrime() for starting deflate output mid-byte -- for appending
- Z_RLE strategy for run-length encoding -- option for PNG compression
- gzclearerr() and gzungetc(), analogous to stdio functions
- inflateCopy() added, analogous to deflateCopy()
- deflateBound() and compressBound() for maximum size of compressed data
- zlibCompileFlags() to provide compilation information
- More supported architectures and improved shared library support
- Many more FAQ entries
- Several new and updated contributions in the contrib directory

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