Remove the deprecation notice for timegm().

The tzcode package marked it dprecated in the late 1980ies
but it is universally supported and here to stay.

Triggered by a question from Rodrigo <hruodr at gmail dot com> on misc@.
William Ahern <william at 25thandclement dot com> listed a number of
sound arguments why it shouldn't be considered deprecated, in
particular that there is no better alternative, in particular none
that is thread-safe.

While here, fix the non-standard section name "NOTES", add the
missing STANDARDS section and provide additional information in the
HISTORY section, based on inspection of C89, C11, POSIX 2008, UNIX
v4 and v5 at TUHS, Tahoe and Reno at the CSRG archives, amd the
SunOS 3.5 and 4.0 manuals on bitsavers.

Reasearch on tzcode and SunOS history done by millert@.
OK millert@ on an earlier version of this patch,
and deraadt@ agrees with the general direction.

1 files changed, 57 insertions, 4 deletions

diff --git a/lib/libc/time/ctime.3 b/lib/libc/time/ctime.3
index 284f5f0d3b2..5000b143c4b 100644
--- a/lib/libc/time/ctime.3
+++ b/lib/libc/time/ctime.3
@@ -1,7 +1,7 @@
-.\"	$OpenBSD: ctime.3,v 1.44 2015/09/14 13:08:01 schwarze Exp $
+.\"	$OpenBSD: ctime.3,v 1.45 2020/04/24 10:32:33 schwarze Exp $
 .\"
 .\"
-.Dd $Mdocdate: September 14 2015 $
+.Dd $Mdocdate: April 24 2020 $
 .Dt CTIME 3
 .Os
 .Sh NAME
@@ -201,7 +201,7 @@ with a negative value for
 .Fa tm_isdst .
 .Pp
 .Fn timegm
-is a deprecated interface that converts the broken-down time, as returned by
+converts the broken-down time, as returned by
 .Fn gmtime ,
 into a calendar time value with the same encoding as that of the values
 returned by the
@@ -295,12 +295,65 @@ UTC leap seconds are loaded from
 .Xr tzset 3 ,
 .Xr tzfile 5 ,
 .Xr zic 8
+.Sh STANDARDS
+The functions
+.Fn asctime ,
+.Fn ctime ,
+.Fn difftime ,
+.Fn gmtime ,
+.Fn localtime ,
+and
+.Fn mktime
+conform to
+.St -ansiC .
+.Pp
+The functions
+.Fn asctime_r ,
+.Fn ctime_r ,
+.Fn gmtime_r ,
+and
+.Fn localtime_r
+conform to
+.St -p1003.1-2008 .
+.Pp
+The functions
+.Fn timegm
+and
+.Fn timelocal
+are extensions to these standards.
 .Sh HISTORY
 A
 .Fn ctime
 function first appeared in
 .At v1 .
-.Sh NOTES
+.Pp
+The functions
+.Fn asctime ,
+.Fn gmtime ,
+and
+.Fn localtime
+first appeared in
+.At v5 ,
+.Fn difftime
+and
+.Fn mktime
+in
+.Bx 4.3 Reno ,
+and
+.Fn timegm
+and
+.Fn timelocal
+in SunOS 4.0.
+.Pp
+The functions
+.Fn asctime_r ,
+.Fn ctime_r ,
+.Fn gmtime_r ,
+and
+.Fn localtime_r
+have been available since since
+.Ox 2.5 .
+.Sh CAVEATS
 The return values
 of the non re-entrant functions
 point to static data;