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glibc/manual/contrib.texi
Paul Eggert ee768a30fe Modernize and fix doc’s “Date and Time” (BZ 31876) 
POSIX.1-2024 (now official) specifies tm_gmtoff and tm_zone.
This is a good time to update the manual’s “Date and Time”
chapter so I went through it, fixed some outdated
stuff that had been in there for decades, and improved it to match
POSIX.1-2024 better and to clarify some implementation-defined
behavior.  Glibc already conforms to POSIX.1-2024 in these matters, so
this is merely a documentation change.

* manual/examples/strftim.c: Use snprintf instead of now-deprecated
  function asctime.  Check for localtime failure.  Simplify by using
  puts instead of fputs.  Prefer ‘buf, sizeof buf’ to less-obvious
  ‘buffer, SIZE’.

* manual/examples/timespec_subtract.c: Modernize to use struct
  timespec not struct timeval, and rename from timeval_subtract.c.
  All uses changed.  Check for overflow.  Do not check for negative
  return value, which ought to be OK since negative time_t is OK.
  Use GNU indenting style.

* manual/time.texi:

  Document CLOCKS_PER_SEC, TIME_UTC, timespec_get, timespec_getres,
  strftime_l.

  Document the storage lifetime of tm_zone and of tzname.

  Caution against use of tzname, timezone and daylight, saying that
  these variables have unspecified values when TZ is geographic.
  This is what glibc actually does (contrary to what the manual said
  before this patch), and POSIX is planned to say the same thing
  <https://austingroupbugs.net/view.php?id=1816>.
  Also say that directly accessing the variables is not thread-safe.

  Say that localtime_r and ctime_r don’t necessarily set time zone
  state.  Similarly, in the tzset documentation, say that it is called
  by ctime, localtime, mktime, strftime, not that it is called by all
  time conversion functions that depend on the time zone.

  Say that tm_isdst is useful mostly just for mktime, and that
  other uses should prefer tm_gmtoff and tm_zone instead.

  Do not say that strftime ignores tm_gmtoff and tm_zone, because
  it doesn’t do that.

  Document what gmtime does to tm_gmtoff and tm_zone.

  Say that the asctime, asctime_r, ctime, and ctime_r are now deprecated
  and/or obsolescent, and that behavior is undefined if the year is <
  1000 or > 9999.  Document strftime before these now-obsolescent
  functions, so that readers see the useful function first.

  Coin the terms “geographical format” and “proleptic format” for the
  two main formats of TZ settings, to simplify exposition.  Use this
  wording consistently.

  Update top-level proleptic syntax to match POSIX.1-2024, which glibc
  already implements.  Document the angle-bracket quoted forms of time
  zone abbreviations in proleptic TZ.  Say that time zone abbreviations
  can contain only ASCII alphanumerics, ‘+’, and ‘-’.

  Document what happens if the proleptic form specifies a DST
  abbreviation and offset but omits the rules.  POSIX says this is
  implementation-defined so we need to document it.  Although this
  documentation mentions ‘posixrules’ tersely, we need to rethink
  ‘posixrules’ since I think it stops working after 2038.

  Clarify wording about TZ settings beginning with ‘;’.

  Say that timegm is in ISO C (as of C23).

  Say that POSIX.1-2024 removed gettimeofday.

  Say that tm_gmtoff and tm_zone are extensions to ISO C, which is
  clearer than saying they are invisible in a struct ISO C enviroment,
  and gives us more wiggle room if we want to make them visible in
  strict ISO C, something that ISO C allows.

  Drop mention of old standards like POSIX.1c and POSIX.2-1992 in the
  text when the history is so old that it’s no longer useful in a
  general-purpose manual.

  Define Coordinated Universal Time (UTC), time zone, time zone ruleset,
  and POSIX Epoch, and use these phrases more consistently.

  Improve TZ examples to show more variety, and to reflect current
  practice and timestamps.  Remove obsolete example about Argentina.
  Add an example for Ireland.

  Don’t rely on GCC extensions when explaining ctime_r.

  Do not say that difftime produces the mathematically correct result,
  since it might be inexact.

  For clock_t don’t say “as in the example above” when there is no
  such example, and don’t say that casting to double works “properly
  and consistently no matter what”, as it suffers from rounding and
  overflow.

  Don’t say broken-down time is not useful for calculations; it’s
  merely painful.

  Say that UTC is not defined before 1960.

  Rename Time Zone Functions to Time Zone State.  All uses changed.

  Update Internet RFC 822 → 5322, 1305 → 5905.  Drop specific years of
  ISO 8601 as they don’t matter.

  Minor style changes: @code{"..."} → @t{"..."} to avoid overquoting in
  info files, @code → @env for environment variables, Daylight Saving
  Time → daylight saving time, white space → whitespace, prime meridian
  → Prime Meridian.
2024-06-15 08:53:50 -07:00

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@node Contributors, Free Manuals, Platform, Top
@c %MENU% Who wrote what parts of the GNU C Library
@appendix Contributors to @theglibc{}
@Theglibc{} project would like to thank its many contributors.
Without them the project would not have been nearly as successful as
it has been. Any omissions in this list are accidental. Feel free to
file a bug in bugzilla if you have been left out or some of your
contributions are not listed. Please keep this list in alphabetical
order.
@itemize @bullet
@item
Nick Alcock for contributing fixes to allow @theglibc{} to be built with the
stack smashing protector enabled.
@item
John David Anglin for various fixes to the hppa port.
@item
Albert ARIBAUD for Y2038 related fixes.
@item
Ryan S. Arnold for his improvements for Linux on PowerPC and his direction
as FSF Project Steward for @theglibc{}.
@item
Arsen Arsenovi@'c for various fixes.
@item
Miles Bader for writing the @code{argp} argument-parsing package, and the
@code{argz}/@code{envz} interfaces.
@item
Ralf B@"achle for contributing @file{fpu_control.h},
@file{regdef.h}, @file{sgidefs.h}, @file{sys/asm.h}, and @file{sys/regdef.h}
under the @file{sysdeps/mips} directory.
@item
Jeff Bailey for his maintainership of the HPPA architecture.
@item
Petr Baudis for bug fixes and testing.
@item
Fr@'ed@'eric B@'erat for numerous fixes and contributions.
@item
Indu Bhagat for various fixes.
@item
Anton Blanchard for various fixes.
@item
Stephen R. van den Berg for contributing a highly-optimized
@code{strstr} function.
@item
Ond@v{r}ej B@'ilka for contributing optimized string routines for x64 and various
fixes.
@item
Eric Blake for adding O(n) implementations of @code{memmem},
@code{strstr} and @code{strcasestr}.
@item
Philip Blundell for the ports to Linux/ARM
(@code{arm-@var{ANYTHING}-linuxaout}) and ARM standalone
(@code{arm-@var{ANYTHING}-none}), as well as for parts of the IPv6
support code.
@item
Mahesh Bodapati for various fixes.
@item
Per Bothner for the implementation of the @code{libio} library which
is used to implement @code{stdio} functions.
@item
Dridi Boukelmoune for various fixes.
@item
Mark Brown for his direction as part of @theglibc{} steering
committee.
@item
Sergey Bugaev for numerous contributions to Hurd.
@item
Thomas Bushnell for his contributions to Hurd.
@item
Yinyu Cai for their maintainership of the LoongArch port.
@item
Rogerio Alves Cardoso for various fixes to PowerPC.
@item
Daniel Cederman for fixes to the Sparc port.
@item
Kito Cheng for various fixes.
@item
Paul Clarke for optimized functions on PowerPC.
@item
Alejandro Colomar for various fixes.
@item
Martin Coufal for various fixes.
@item
Mike Crowe for various fixes.
@item
Flavio Cruz for contributions to Hurd.
@item
Palmer Dabbelt for contributing the port to Linux/RISC-V.
@item
DJ Delorie for maintenance of Linux/RISC-V, and various fixes.
@item
Jianbo Deng for the work on the Loongson port.
@item
Wilco Dijkstra for various fixes and work on the AArch64 port.
@item
Liubov Dmitrieva for optimized string and math functions on x86-64 and
x86.
@item
Michael Hudson Doyle for various fixes.
@item
Ulrich Drepper for his many contributions in almost all parts of
@theglibc{}, including:
@itemize @bullet
@item writing most of the POSIX Threads Library originally.
@item internationalization support, including the @code{locale} and
@code{localedef} utilities.
@item Linux i386/ELF support
@item the @code{hsearch} and @code{drand48} families of functions,
reentrant @samp{@dots{}@code{_r}} versions of the @code{random}
family; System V shared memory and IPC support code
@item several highly-optimized string functions for i@var{x}86
processors
@item many math functions
@item the character conversion functions (@code{iconv})
@item the @code{ftw} and @code{nftw} functions
@item the floating-point printing function used by @code{printf} and friends
and the floating-point reading function used by @code{scanf},
@code{strtod} and friends
@item the @code{catgets} support and the entire suite of multi-byte
and wide-character support functions (@file{wctype.h}, @file{wchar.h}, etc.).
@item versioning of objects on the symbol level
@end itemize
@item
Richard Earnshaw for continued support and fixes to the various ARM
machine files.
@item
Paul Eggert for the @code{mktime} function, for his direction as
part of @theglibc{} steering committee, and numerous fixes.
@item
Roy Eldar for various fixes.
@item
Steve Ellcey for various fixes.
@item
Mike FABIAN for automating Unicode updates, for updating the locale data
for ISO 14651, for updating the library Unicode support, and for many
locale updates and fixes.
@item
Tulio Magno Quites Machado Filho for adding a new class of installed
headers for low-level platform-specific functionality, including the
low-level platform-specific headers for PowerPC, for their maintainership
of the PowerPC port and various fixes.
@item
Olaf Flebbe and Ralf B@"achle for contributing
@file{sysdeps/mips/fpu_control.h}.
@item
Alistair Francis for Y2038 related fixes.
@item
Mike Frysinger for his maintaining of the IA64 architecture and for
testing and bug fixing.
@item
Martin Galvan for contributing gdb pretty printer support to glibc and adding
an initial set of pretty printers for structures in the POSIX Threads library.
@item
Romain Geissler for various fixes.
@item
Michael Glad for the passphrase-hashing function @code{crypt} and related
functions (no longer part of glibc, but we still appreciate his work).
@item
Wolfram Gloger for contributing the memory allocation functions
functions @code{malloc}, @code{realloc} and @code{free} and related
code.
@item
Noah Goldstein for contributing extensive x86 / x86-64 optimizations.
@item
Gabriel F. T. Gomes for his improvements for Linux on PowerPC and for
implementing the IEEE 128-bit floating point type for PowerPC.
@item
Torbj@"orn Granlund for fast implementations of many of the string
functions (@code{memcpy}, @code{strlen}, etc.).
@item
Vineet Gupta for their maintainership of the ARC port.
@item
Michael J. Haertel for writing the merge sort function @code{qsort}
and malloc checking functions like @code{mcheck}.
@item
Bruno Haible for his improvements to the @code{iconv} and locale
implementations and various fixes.
@item
Mao Han for the C-SKY port.
@item
Richard Henderson for the port to Linux on Alpha
(@code{alpha-@var{anything}-linux}) and software floating-point support.
@item
David Holsgrove for the port to Linux on MicroBlaze.
@item
Leonhard Holz for various fixes.
@item
Stafford Horne for maintainership of the OpenRISC port.
@item
Ying Huang for work on the MIPS port.
@item
Guy-Fleury Iteriteka for contributions to Hurd support.
@item
Daniel Jacobowitz for various fixes and enhancements.
@item
Andreas Jaeger for the port to Linux on x86-64
(@code{x86_64-@var{anything}-linux} and his work on Linux for MIPS
(@code{mips-@var{anything}-linux}), implementing the @file{ldconfig}
program, providing a test suite for the math library and for his
direction as part of @theglibc{} steering committee.
@item
Sam James for various fixes.
@item
Aurelien Jarno for various fixes.
@item
Rical Jasan for contributing various fixes in @theglibc{} manual.
@item
Jakub Jelinek for implementing a number of checking functions,
software floating-point support and for
his direction as part of @theglibc{} steering committee.
@item
Simon Josefsson for the @code{libidn} add-on.
@item
Geoffrey Keating for the port to Linux on PowerPC
(@code{powerpc-@var{anything}-linux}).
@item
Brendan Kehoe for contributing the port to the MIPS DECStation running
Ultrix 4 (@code{mips-dec-ultrix4}) and the port to the DEC Alpha
running OSF/1 (@code{alpha-dec-osf1}).
@item
Mark Kettenis for implementing the @code{utmpx} interface and a utmp
daemon, and for a Hesiod NSS module.
@item
Simon Kissane for gmon improvements.
@item
Andi Kleen for implementing pthreads lock elision with TSX.
@item
Kazumoto Kojima for the port of the Mach and Hurd code to the MIPS
architecture (@code{mips-@var{anything}-gnu}) and for his work on the
SH architecture.
@item
Pavel Kozlov for maintainership of the ARC port.
@item
Maxim Kuvyrkov for various fixes.
@item
Andreas Krebbel for his work on Linux for s390 and s390x.
@item
Thorsten Kukuk for providing an implementation for NIS (YP) and NIS+,
securelevel 0, 1 and 2 and for the implementation for a caching daemon
for NSS (@file{nscd}).
@item
Akhilesh Kumar for various fixes to locales.
@item
Jeff Law for various fixes.
@item
Doug Lea for contributing the memory allocation functions
@code{malloc}, @code{realloc} and @code{free} and related
code.
@item
Chris Leonard for various fixes and enhancements to localedata.
@item
Ilya Leoshkevich for various fixes.
@item
Dmitry V. Levin for various fixes.
@item
Stefan Liebler for numerous fixes and the work on the S390 port.
@item
Hongjiu Lu for providing the support for a Linux 32-bit runtime
environment under x86-64 (x32), for porting to Linux on IA64, for
improved string functions, a framework for testing IFUNC
implementations, for implementing Intel Control-Flow Enforcement
Technology, and many bug fixes.
@item
Rafa@l{} Lu@dotaccent{z}y@'nski
for contributing support for two grammatical forms of month
names, and for various fixes to locales.
@item
Maxim Kuvyrkov for various fixes.
@item
Luis Machado for optimized functions on PowerPC.
@item
David J. MacKenzie for his contribution to the @code{getopt}
function and writing the @file{tar.h} header.
@item
Lukasz Majewski for Y2038 related fixes.
@item
Greg McGary for adding runtime support for bounds checking.
@item
Roland McGrath for writing most of @theglibc{} originally, for his
work on the Hurd port, his direction as part of @theglibc{} steering
committee and as FSF Project Steward for @theglibc{}, and for many bug
fixes and reviewing of contributions.
@item
Allan McRae for various fixes.
@item
Jason Merrill for the port to the Sequent Symmetry running Dynix
version 3 (@code{i386-sequent-bsd}).
@item
Chris Metcalf for the port to Linux/Tile
(@code{tilegx-@var{anything}-linux} and
@code{tilepro-@var{anything}-linux}) and support for the generic Linux
kernel syscall interface used by several newer ports.
@item
Jim Meyering for various fixes.
@item
David Miller for contributing the port to Linux/Sparc
(@code{sparc*-@var{anything}-linux}).
@item
Cupertino Miranda for various fixes.
@item
Alan Modra for his improvements for Linux on PowerPC.
@item
Sachin Monga for various fixes.
@item
David Mosberger-Tang for contributing the port to Linux/Alpha
(@code{alpha-@var{anything}-linux}).
@item
Wainer dos Santos Moschetta for various fixes to powerpc.
@item
Stephen Moshier for implementing some 128-bit long double format math
functions.
@item
Stephen Munroe for his port to Linux on PowerPC64
(@code{powerpc64-@var{anything}-linux}) and for adding optimized
implementations for PowerPC.
@item
Paul E. Murphy for various fixes on PowerPC and for implementing the IEEE
128-bit floating point type for PowerPC.
@item
Joseph S. Myers for numerous bug fixes for the libm functions, for
his maintainership of the ARM and MIPS architectures and the math
component, improving cross-compilation and cross-testing of
@theglibc{}, expanded coverage of conformtest, merging the ports/
subdirectory into the @glibcadj{} main repository, C23 support,
and his direction as FSF Project Steward for @theglibc{}.
@item
Marko Myllynen for various fixes.
@item
Szabolcs Nagy for various fixes and contributions to AArch64.
@item
Nab for various fixes.
@item
Will Newton for contributing some optimized string functions and pointer
encryption support for ARM and various fixes.
@item
Carlos O'Donell for his maintainership of the HPPA architecture, for
maintaining @theglibc{} web pages and wiki, for his direction as FSF
Project Steward for @theglibc{} and various bug fixes.
@item
Alexandre Oliva for adding TLS descriptors for LD and GD on x86 and
x86-64, for the am33 port, for completing the MIPS n64/n32/o32 multilib
port, for thread-safety, async-signal safety and async-cancellation
safety documentation in the manual, for his direction as FSF Project
Maintainer and for various fixes.
@item
Sunil K. Pandey for various fixes.
@item
Ronan Pigott for various fixes.
@item
Paul Pluzhnikov for various fixes.
@item
Marek Polacek for various fixes.
@item
Siddhesh Poyarekar for various fixes, an implementation of a framework for
performance benchmarking of functions and implementing the tunables
infrastructure.
@item
Tom Quinn for contributing the startup code to support SunOS shared
libraries and the port to SGI machines running Irix 4
(@code{mips-sgi-irix4}).
@item
Joe Ramsay for contributing to the AArch64 port, in particular the
vector library.
@item
Torvald Riegel for the implementation of new algorithms for semaphores,
pthread_rwlock and condition variables.
@item
Maciej W. Rozycki for MIPS fixes, support for ABSOLUTE symbols,
and various fixes.
@item
Leonardo Sandoval for various fixes.
@item
Pravin Satpute for writing sorting rules for some Indian languages.
@item
Douglas C. Schmidt for writing the quick sort function used as a
fallback by @code{qsort}.
@item
Will Schmidt for optimized string functions on PowerPC.
@item
Andreas Schwab for the port to Linux/m68k
(@code{m68k-@var{anything}-linux}), for his direction as part of
@theglibc{} steering committee, and for various bug fixes.
@item
Martin Schwidefsky for porting to Linux on s390
(@code{s390-@var{anything}-linux}) and s390x
(@code{s390x-@var{anything}-linux}).
@item
Thomas Schwinge for his contribution to Hurd and the SH architecture.
@item
Martin Sebor for various fixes.
@item
Andrew Senkevich for contributing vector math function implementations for x86.
@item
Carlos Eduardo Seo for optimized functions on PowerPC.
@item
Arjun Shankar for testing and bug fixing.
@item
Marcus Shawcroft for contributing the AArch64 port.
@item
TAMUKI Shoichi for various fixes.
@item
Joe Simmons-Talbott for various fixes.
@item
Franz Sirl for various fixes.
@item
Gavin Smith for various fixes.
@item
Jes Sorensen for porting to Linux on IA64 (@code{ia64-@var{anything}-linux}).
@item
Julian Squires for various fixes.
@item
Rajalakshmi Srinivasaraghavan for various fixes and optimizations on PowerPC,
for implementing the IEEE 128-bit floating point type for PowerPC., and for
their maintainership of the PowerPC port.
@item
Richard Stallman for his contribution to the @code{getopt} function.
@item
Alfred M. Szmidt for various fixes.
@item
Chung-Lin Tang for contributing the Nios II port.
@item
Ian Lance Taylor for contributing the port to the MIPS DECStation
running Ultrix 4 (@code{mips-dec-ultrix4}).
@item
Samuel Thibault for numerous improvements to the Hurd port.
@item
Pino Toscano for various fixes.
@item
Matt Turner for various fixes to the Alpha port.
@item
Valery Ushakov for locale fixes.
@item
Hsiangkai Wang for various fixes.
@item
Tim Waugh for the implementation of the POSIX.2 @code{wordexp}
function family.
@item
Ulrich Weigand for various fixes to the PowerPC64 and Arm ports.
@item
Florian Weimer for his maintainership of the network component, for handling
of security issues, and for numerous fixes and contributions.
@item
Zack Weinberg for the @code{explicit_bzero} implementation and for various
fixes.
@item
Mark Wielaard for various fixes.
@item
Xi Ruoyao for various fixes.
@item
Qixing ksyx Xue for various fixes.
@item
Adam Yi for various fixes.
@item
Eric Youngdale for implementing versioning of objects on the symbol level.
@item
Adhemerval Zanella for optimized functions on PowerPC, ISO C threads support,
the work on tunables, and numerous contributions and fixes.
@item
Xuelei Zhang for optimized functions on AArch64.
@end itemize
Some code in @theglibc{} comes from other projects and might be under
a different license:
@itemize @bullet
@item
The time zone support code is derived from the public-domain time zone
package by Arthur David Olson and his many contributors.
@item
Some of the support code for Mach is taken from Mach 3.0 by CMU;
the file @file{if_ppp.h} is also copyright by CMU, but under a different license;
see the file @file{LICENSES} for the text of the licenses.
@item
The random number generation functions @code{random}, @code{srandom},
@code{setstate} and @code{initstate}, which are also the basis for the
@code{rand} and @code{srand} functions, were written by Earl T. Cohen
for the University of California at Berkeley and are copyrighted by the
Regents of the University of California. They have undergone minor
changes to fit into @theglibc{} and to fit the @w{ISO C} standard,
but the functional code is Berkeley's.
@item
The Internet-related code (most of the @file{inet} subdirectory) and
several other miscellaneous functions and header files have been
included from 4.4 BSD with little or no modification. The copying
permission notice for this code can be found in the file @file{LICENSES}
in the source distribution.
@item
The @code{getaddrinfo} and @code{getnameinfo} functions and supporting
code were written by Craig Metz; see the file @file{LICENSES} for
details on their licensing.
@item
The DNS resolver code is taken directly from BIND 8.2.3-T5B, which
includes copyrighted code from UC Berkeley and from Digital Equipment
Corporation. See the file @file{LICENSES} for the text of the DEC license.
@item
The code to support Sun RPC is taken verbatim from Sun's
@w{@sc{rpcsrc-4.0}} distribution; see the file @file{LICENSES} for the
text of the license.
@item
The math functions are taken from @code{fdlibm-5.1} by Sun
Microsystems, as modified by J.T. Conklin, Ian Lance Taylor,
Ulrich Drepper, Andreas Schwab, and Roland McGrath.
@item
Many of the IEEE 64-bit double precision math functions
(in the @file{sysdeps/ieee754/dbl-64} subdirectory) come
from the IBM Accurate Mathematical Library, contributed by IBM.
@item
Many of the IA64 math functions are taken from a collection of
``Highly Optimized Mathematical Functions for Itanium'' that Intel
makes available under a free license; see the file @file{LICENSES} for
details.
@end itemize
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