gzip/README - maze/klibc - Git at Google

 This is the file README for the gzip distribution, version 1.2.4.

 gzip (GNU zip) is a compression utility designed to be a replacement
 for 'compress'. Its main advantages over compress are much better
 compression and freedom from patented algorithms.  The GNU Project
 uses it as the standard compression program for its system.

 gzip currently uses by default the LZ77 algorithm used in zip 1.9 (the
 portable pkzip compatible archiver). The gzip format was however
 designed to accommodate several compression algorithms. See below
 for a comparison of zip and gzip.

 gunzip can currently decompress files created by gzip, compress or
 pack. The detection of the input format is automatic.  For the
 gzip format, gunzip checks a 32 bit CRC. For pack, gunzip checks the
 uncompressed length.  The 'compress' format was not designed to allow
 consistency checks. However gunzip is sometimes able to detect a bad
 .Z file because there is some redundancy in the .Z compression format.
 If you get an error when uncompressing a .Z file, do not assume that
 the .Z file is correct simply because the standard uncompress does not
 complain.  This generally means that the standard uncompress does not
 check its input, and happily generates garbage output.

 gzip produces files with a .gz extension. Previous versions of gzip
 used the .z extension, which was already used by the 'pack'
 Huffman encoder. gunzip is able to decompress .z files (packed
 or gzip'ed).

 Several planned features are not yet supported (see the file TODO).
 See the file NEWS for a summary of changes since 0.5.  See the file
 INSTALL for installation instructions. Some answers to frequently
 asked questions are given in the file INSTALL, please read it. (In
 particular, please don't ask me once more for an /etc/magic entry.)

 WARNING: on several systems, compiler bugs cause gzip to fail, in
 particular when optimization options are on.  See the section "Special
 targets" at the end of the INSTALL file for a list of known problems.
 For all machines, use "make check" to check that gzip was compiled
 correctly.  Try compiling gzip without any optimization if you have a
 problem.

 Please send all comments and bug reports by electronic mail to:
    Jean-loup Gailly <jloup@chorus.fr>

 or, if this fails, to bug-gnu-utils@prep.ai.mit.edu.
 Bug reports should ideally include:

     * The complete output of "gzip -V" (or the contents of revision.h
       if you can't get gzip to compile)
     * The hardware and operating system (try "uname -a")
     * The compiler used to compile (if it is gcc, use "gcc -v")
     * A description of the bug behavior
     * The input to gzip, that triggered the bug

 If you send me patches for machines I don't have access to, please test them
 very carefully. gzip is used for backups, it must be extremely reliable.

 The package crypt++.el is highly recommended to manipulate gzip'ed
 file from emacs. It recognizes automatically encrypted and compressed
 files when they are first visited or written. It is available via
 anonymous ftp to roebling.poly.edu [128.238.5.31] in /pub/crypt++.el.
 The same directory contains also patches to dired, ange-ftp and info.
 GNU tar 1.11.2 has a -z option to invoke directly gzip, so you don't have to
 patch it. The package ftp.uu.net:/languages/emacs-lisp/misc/jka-compr19.el.Z
 also supports gzip'ed files.

 The znew and gzexe shell scripts provided with gzip benefit from
 (but do not require) the cpmod utility to transfer file attributes.
 It is available by anonymous ftp on gatekeeper.dec.com in
 /.0/usenet/comp.sources.unix/volume11/cpmod.Z.

 The sample programs zread.c, sub.c and add.c in subdirectory sample
 are provided as examples of useful complements to gzip. Read the
 comments inside each source file.  The perl script ztouch is also
 provided as example (not installed by default since it relies on perl).


 gzip is free software, you can redistribute it and/or modify it under
 the terms of the GNU General Public License, a copy of which is
 provided under the name COPYING. The latest version of gzip are always
 available by ftp in prep.ai.mit.edu:/pub/gnu, or in any of the prep
 mirror sites:

 - sources in gzip-*.tar (or .shar or .tar.gz).
 - Solaris 2 executables in sparc-sun-solaris2/gzip-binaries-*.tar
 - MSDOS lha self-extracting exe in gzip-msdos-*.exe. Once extracted,
   copy gzip.exe to gunzip.exe and zcat.exe, or use "gzip -d" to decompress.
   gzip386.exe runs much faster but only on 386 and above; it is compiled with
   djgpp 1.10 available in directory omnigate.clarkson.edu:/pub/msdos/djgpp.

 A VMS executable is available in ftp.spc.edu:[.macro32.savesets]gzip-1-*.zip
 (use [.macro32]unzip.exe to extract). A PRIMOS executable is available
 in ftp.lysator.liu.se:/pub/primos/run/gzip.run.
 OS/2 executables (16 and 32 bits versions) are available in
 ftp.tu-muenchen.de:/pub/comp/os/os2/archiver/gz*-[16,32].zip

 Some ftp servers can automatically make a tar.Z from a tar file. If
 you are getting gzip for the first time, you can ask for a tar.Z file
 instead of the much larger tar file.

 Many thanks to those who provided me with bug reports and feedback.
 See the files THANKS and ChangeLog for more details.


 		Note about zip vs. gzip:

 The name 'gzip' was a very unfortunate choice, because zip and gzip
 are two really different programs, although the actual compression and
 decompression sources were written by the same persons. A different
 name should have been used for gzip, but it is too late to change now.

 zip is an archiver: it compresses several files into a single archive
 file. gzip is a simple compressor: each file is compressed separately.
 Both share the same compression and decompression code for the
 'deflate' method.  unzip can also decompress old zip archives
 (implode, shrink and reduce methods). gunzip can also decompress files
 created by compress and pack. zip 1.9 and gzip do not support
 compression methods other than deflation. (zip 1.0 supports shrink and
 implode). Better compression methods may be added in future versions
 of gzip. zip will always stick to absolute compatibility with pkzip,
 it is thus constrained by PKWare, which is a commercial company.  The
 gzip header format is deliberately different from that of pkzip to
 avoid such a constraint.

 On Unix, gzip is mostly useful in combination with tar. GNU tar
 1.11.2 has a -z option to invoke gzip automatically.  "tar -z"
 compresses better than zip, since gzip can then take advantage of
 redundancy between distinct files. The drawback is that you must
 scan the whole tar.gz file in order to extract a single file near
 the end; unzip can directly seek to the end of the zip file. There
 is no overhead when you extract the whole archive anyway.
 If a member of a .zip archive is damaged, other files can still
 be recovered. If a .tar.gz file is damaged, files beyond the failure
 point cannot be recovered. (Future versions of gzip will have
 error recovery features.)

 gzip and gunzip are distributed as a single program. zip and unzip
 are, for historical reasons, two separate programs, although the
 authors of these two programs work closely together in the info-zip
 team. zip and unzip are not associated with the GNU project.
 The sources are available by ftp in

 	 oak.oakland.edu:/pub/misc/unix/zip19p1.zip
 	 oak.oakland.edu:/pub/misc/unix/unz50p1.tar-z
	This is the file README for the gzip distribution, version 1.2.4.

	gzip (GNU zip) is a compression utility designed to be a replacement
	for 'compress'. Its main advantages over compress are much better
	compression and freedom from patented algorithms. The GNU Project
	uses it as the standard compression program for its system.

	gzip currently uses by default the LZ77 algorithm used in zip 1.9 (the
	portable pkzip compatible archiver). The gzip format was however
	designed to accommodate several compression algorithms. See below
	for a comparison of zip and gzip.

	gunzip can currently decompress files created by gzip, compress or
	pack. The detection of the input format is automatic. For the
	gzip format, gunzip checks a 32 bit CRC. For pack, gunzip checks the
	uncompressed length. The 'compress' format was not designed to allow
	consistency checks. However gunzip is sometimes able to detect a bad
	.Z file because there is some redundancy in the .Z compression format.
	If you get an error when uncompressing a .Z file, do not assume that
	the .Z file is correct simply because the standard uncompress does not
	complain. This generally means that the standard uncompress does not
	check its input, and happily generates garbage output.

	gzip produces files with a .gz extension. Previous versions of gzip
	used the .z extension, which was already used by the 'pack'
	Huffman encoder. gunzip is able to decompress .z files (packed
	or gzip'ed).

	Several planned features are not yet supported (see the file TODO).
	See the file NEWS for a summary of changes since 0.5. See the file
	INSTALL for installation instructions. Some answers to frequently
	asked questions are given in the file INSTALL, please read it. (In
	particular, please don't ask me once more for an /etc/magic entry.)

	WARNING: on several systems, compiler bugs cause gzip to fail, in
	particular when optimization options are on. See the section "Special
	targets" at the end of the INSTALL file for a list of known problems.
	For all machines, use "make check" to check that gzip was compiled
	correctly. Try compiling gzip without any optimization if you have a
	problem.

	Please send all comments and bug reports by electronic mail to:
	Jean-loup Gailly <jloup@chorus.fr>

	or, if this fails, to bug-gnu-utils@prep.ai.mit.edu.
	Bug reports should ideally include:

	* The complete output of "gzip -V" (or the contents of revision.h
	if you can't get gzip to compile)
	* The hardware and operating system (try "uname -a")
	* The compiler used to compile (if it is gcc, use "gcc -v")
	* A description of the bug behavior
	* The input to gzip, that triggered the bug

	If you send me patches for machines I don't have access to, please test them
	very carefully. gzip is used for backups, it must be extremely reliable.

	The package crypt++.el is highly recommended to manipulate gzip'ed
	file from emacs. It recognizes automatically encrypted and compressed
	files when they are first visited or written. It is available via
	anonymous ftp to roebling.poly.edu [128.238.5.31] in /pub/crypt++.el.
	The same directory contains also patches to dired, ange-ftp and info.
	GNU tar 1.11.2 has a -z option to invoke directly gzip, so you don't have to
	patch it. The package ftp.uu.net:/languages/emacs-lisp/misc/jka-compr19.el.Z
	also supports gzip'ed files.

	The znew and gzexe shell scripts provided with gzip benefit from
	(but do not require) the cpmod utility to transfer file attributes.
	It is available by anonymous ftp on gatekeeper.dec.com in
	/.0/usenet/comp.sources.unix/volume11/cpmod.Z.

	The sample programs zread.c, sub.c and add.c in subdirectory sample
	are provided as examples of useful complements to gzip. Read the
	comments inside each source file. The perl script ztouch is also
	provided as example (not installed by default since it relies on perl).


	gzip is free software, you can redistribute it and/or modify it under
	the terms of the GNU General Public License, a copy of which is
	provided under the name COPYING. The latest version of gzip are always
	available by ftp in prep.ai.mit.edu:/pub/gnu, or in any of the prep
	mirror sites:

	- sources in gzip-*.tar (or .shar or .tar.gz).
	- Solaris 2 executables in sparc-sun-solaris2/gzip-binaries-*.tar
	- MSDOS lha self-extracting exe in gzip-msdos-*.exe. Once extracted,
	copy gzip.exe to gunzip.exe and zcat.exe, or use "gzip -d" to decompress.
	gzip386.exe runs much faster but only on 386 and above; it is compiled with
	djgpp 1.10 available in directory omnigate.clarkson.edu:/pub/msdos/djgpp.

	A VMS executable is available in ftp.spc.edu:[.macro32.savesets]gzip-1-*.zip
	(use [.macro32]unzip.exe to extract). A PRIMOS executable is available
	in ftp.lysator.liu.se:/pub/primos/run/gzip.run.
	OS/2 executables (16 and 32 bits versions) are available in
	ftp.tu-muenchen.de:/pub/comp/os/os2/archiver/gz*-[16,32].zip

	Some ftp servers can automatically make a tar.Z from a tar file. If
	you are getting gzip for the first time, you can ask for a tar.Z file
	instead of the much larger tar file.

	Many thanks to those who provided me with bug reports and feedback.
	See the files THANKS and ChangeLog for more details.


	Note about zip vs. gzip:

	The name 'gzip' was a very unfortunate choice, because zip and gzip
	are two really different programs, although the actual compression and
	decompression sources were written by the same persons. A different
	name should have been used for gzip, but it is too late to change now.

	zip is an archiver: it compresses several files into a single archive
	file. gzip is a simple compressor: each file is compressed separately.
	Both share the same compression and decompression code for the
	'deflate' method. unzip can also decompress old zip archives
	(implode, shrink and reduce methods). gunzip can also decompress files
	created by compress and pack. zip 1.9 and gzip do not support
	compression methods other than deflation. (zip 1.0 supports shrink and
	implode). Better compression methods may be added in future versions
	of gzip. zip will always stick to absolute compatibility with pkzip,
	it is thus constrained by PKWare, which is a commercial company. The
	gzip header format is deliberately different from that of pkzip to
	avoid such a constraint.

	On Unix, gzip is mostly useful in combination with tar. GNU tar
	1.11.2 has a -z option to invoke gzip automatically. "tar -z"
	compresses better than zip, since gzip can then take advantage of
	redundancy between distinct files. The drawback is that you must
	scan the whole tar.gz file in order to extract a single file near
	the end; unzip can directly seek to the end of the zip file. There
	is no overhead when you extract the whole archive anyway.
	If a member of a .zip archive is damaged, other files can still
	be recovered. If a .tar.gz file is damaged, files beyond the failure
	point cannot be recovered. (Future versions of gzip will have
	error recovery features.)

	gzip and gunzip are distributed as a single program. zip and unzip
	are, for historical reasons, two separate programs, although the
	authors of these two programs work closely together in the info-zip
	team. zip and unzip are not associated with the GNU project.
	The sources are available by ftp in

	oak.oakland.edu:/pub/misc/unix/zip19p1.zip
	oak.oakland.edu:/pub/misc/unix/unz50p1.tar-z