zlib

zlib is a software library for data compression, implemented in C, providing in-memory compression and decompression with streaming interfaces. It implements the DEFLATE compression algorithm (RFC 1951) and provides two wrapper formats: the zlib data format (RFC 1950) and the gzip file format (RFC 1952). It is designed for speed and reasonable compression.

The library exposes deflate and inflate functions using a z_stream structure; it supports compression levels 0–9 and operates in a streaming fashion with large buffers. Parameters such as window bits and memory usage can be tuned to balance speed, memory consumption, and compression efficiency. For data integrity, the zlib data format uses an Adler-32 checksum, while the gzip wrapper uses a CRC-32 checksum.

zlib is written in portable ANSI C and is widely available on major platforms, including Unix-like systems and Windows. It is distributed under the zlib License, a permissive free software license that allows use in proprietary and open-source software with minimal restrictions.

Developed by Jean-loup Gailly and Mark Adler, zlib was first released in 1995 and has since become a de facto standard for general purpose data compression. It underpins a range of widely used technologies and formats, including the PNG image format, the gzip file format, and numerous network and software applications that require efficient, portable compression.