Tool for easily analyzing, compressing, and decompressing files with the ZLIB format (RFC 1950). Reduce data size for storage and web transfer with Zlib compression.
ZLIB Compression - dCode
Tag(s) : Compression
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ZLIB Compression
ZLIB Decompressor
ZLIB Compressor
Answers to Questions (FAQ)
What is ZLIB? (Definition)
Zlib is a free software compression library that implements the Deflate algorithm. It provides functions for compressing and decompressing data in memory.
The Zlib encapsulation format, defined by RFC 1950, specifies the structure of the compressed stream (header, parameters, Adler-32 checksum).
How does compression with ZLIB work?
Zlib compresses a data stream by applying the Deflate algorithm in three steps:
— Identify repeated sequences using LZ77
— Encode the result with Huffman trees
— Encapsulate the Deflate stream in a Zlib container including a header and an Adler-32 checksum.
This process reduces data size without loss, optimizing transfer and storage.
How does decompression with ZLIB work?
Decompressing a Zlib stream involves reading its two header bytes, which specify the Deflate method and associated parameters, and then decoding the Deflate stream contained within the encapsulation.
The reconstructed stream combines LZ77 matching and Huffman decoding.
Once the data is obtained, Zlib verifies its integrity by recalculating the Adler-32 checksum.
What is the difference between Zlib, Deflate and GZIP?
Deflate is a lossless compression algorithm defined by RFC 1951.
Zlib is a library that implements Deflate and provides a lightweight container defined by RFC 1950.
'Gzip' is a file format and tool (RFC 1952) that encapsulates a Deflate stream in its own header and checksum.
In summary: Deflate is the algorithm, Zlib is the library and its container, and Gzip is a software program and also a format that encapsulates Deflate.
How to recognize a ZLIB stream? (Identification)
A Zlib stream begins with two header bytes called CMF (Compression Method and Flags) and FLG (FLaGs).
CMF indicates the compression method (08 for Deflate) and the window size.
FLG encodes various options, including a validity check field.
Example: Zlib magic signatures are frequently '78 9C', '78 01', or '78 DA'.
The end of the stream contains an Adler-32 checksum used to verify data integrity.
When was ZLIB invented?
Zlib was created in 1995 by Jean-loup Gailly and Mark Adler as part of the project to replace the compress format, and initially published with version 1.0 of the gzip software.
How to calculate the Adler-32 checksum?
Calculating an Adler32 checksum involves iterating through the data byte by byte while maintaining two accumulators:
— s1 = (s1 + byte) mod 65521
— s2 = (s2 + s1) mod 65521
The final value is (s2 << 16) + s1.
The prime number 65521 is chosen to limit overflows while ensuring fast integrity checking.
Source code
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