Template:Zlib Header

Zlib Header (more info here and here)

byte index	bit 7	bit 6	bit 5	bit 4	bit 3	bit 2	bit 1	bit 0
[0] CMF	Compression info 7 = indicates a 32K window size				Compression method 8 = denotes the "deflate" compression
[1] FLG	FLEVEL 0 - compressor used fastest algorithm 1 - compressor used fast algorithm 2 - compressor used default algorithm 3 - compressor used maximum compression, slowest algorithm		FDICT (Preset dictionary) If set, a DICT dictionary identifier is present immediately after the FLG byte. The dictionary is a sequence of bytes which are initially fed to the compressor without producing any compressed output. DICT is the Adler-32 checksum of this sequence of bytes (see the definition of ADLER32 below). The decompressor can use this identifier to determine which dictionary has been used by the compressor.	FCHECK value must be such that CMF and FLG, when viewed as a 16-bit unsigned integer stored in MSB order (CMF *256 + FLG), is a multiple of 31.