[Bug manual/31808] New: The supported time_t range is not documented.

[Bug manual/31808] New: The supported time_t range is not documented.

[vincent-srcware at vinc17 dot net]

https://sourceware.org/bugzilla/show_bug.cgi?id=31808

            Bug ID: 31808
           Summary: The supported time_t range is not documented.
           Product: glibc
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: manual
          Assignee: unassigned at sourceware dot org
          Reporter: vincent-srcware at vinc17 dot net
                CC: mtk.manpages at gmail dot com
  Target Milestone: ---

The ISO C17 standard says about time_t:

  The range and precision of times representable in clock_t and time_t
  are implementation-defined.

The glibc manual says that time_t is an integer, but nothing about the actual
supported range (for positive and negative values):

 -- Data Type: time_t

     ‘time_t’ is the simplest data type used to represent simple
     calendar time.

     In ISO C, ‘time_t’ can be either an integer or a floating-point
     type, and the meaning of ‘time_t’ values is not specified.  The
     only things a strictly conforming program can do with ‘time_t’
     values are: pass them to ‘difftime’ to get the elapsed time between
     two simple calendar times (*note Calculating Elapsed Time::), and
     pass them to the functions that convert them to broken-down time
     (*note Broken-down Time::).

     On POSIX-conformant systems, ‘time_t’ is an integer type and its
     values represent the number of seconds elapsed since the “epoch”,
     which is 00:00:00 on January 1, 1970, Coordinated Universal Time.

     The GNU C Library additionally guarantees that ‘time_t’ is a signed
     type, and that all of its functions operate correctly on negative
     ‘time_t’ values, which are interpreted as times before the epoch.

This is important, because if values > 2^52 are officially supported in
magnitude, the difftime() function would have to round the result, and the
exact behavior is not documented in such a case, e.g. which rounding mode is
used and whether an "inexact" exception may be signaled (with the consequence
that difftime() may not be a pure function, due to a side effect).

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[Bug manual/31808] The supported time_t range is not documented.

[gabravier at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=31808

Gabriel Ravier <gabravier at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |gabravier at gmail dot com

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[Bug manual/31808] The supported time_t range is not documented.

[eggert at cs dot ucla.edu]

https://sourceware.org/bugzilla/show_bug.cgi?id=31808

eggert at cs dot ucla.edu changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |eggert at cs dot ucla.edu

--- Comment #1 from eggert at cs dot ucla.edu ---
Created attachment 15539
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15539&action=edit
Remove incorrect attrs from difftime decls

Thanks for reporting the problem. This is a bug in the code, not just the
documentation. Proposed code patch attached.

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[Bug manual/31808] The supported time_t range is not documented.

[eggert at cs dot ucla.edu]

https://sourceware.org/bugzilla/show_bug.cgi?id=31808

eggert at cs dot ucla.edu changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
           Assignee|unassigned at sourceware dot org   |eggert at cs dot ucla.edu
   Last reconfirmed|                            |2024-05-28
             Status|UNCONFIRMED                 |ASSIGNED

--- Comment #2 from eggert at cs dot ucla.edu ---
Created attachment 15542
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15542&action=edit
Improve doc for time_t range

... and here is a patch to the documentation

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[Bug time/31808] The supported time_t range is not documented.

[eggert at cs dot ucla.edu]

https://sourceware.org/bugzilla/show_bug.cgi?id=31808

eggert at cs dot ucla.edu changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |2.40
          Component|manual                      |time

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[Bug time/31808] The supported time_t range is not documented.

[eggert at cs dot ucla.edu]

https://sourceware.org/bugzilla/show_bug.cgi?id=31808

eggert at cs dot ucla.edu changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #3 from eggert at cs dot ucla.edu ---
Documentation problem fixed in commit 400bdb5c85af5a52b3f5653357c9fca87f036bd3
dated Tue May 28 10:07:47 2024 -0700 titled "Improve doc for time_t range (BZ
31808)". Code problem fixed in commit cafef3eb21db24f2e8113b0adc12c0f15d4dec41
dated Tue May 28 10:07:47 2024 -0700 titled "difftime can throw exceptions".

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