bug#19874: 25.0.50; encode-time not working as expected

[ashish.is@lostca.se (Ashish SHUKLA)]

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On Wed, 25 Feb 2015 09:41:45 -0800, Paul Eggert <eggert@cs.ucla.edu> said:
| Thanks for the bug report.  My guess is that there's an
| incompatibility with FreeBSD 10.1 amd64 mktime.  I can't reproduce the
| problem on FreeBSD 9.1 x86.

| Please try the attached patch, just for debugging, and then run the
| following one-line shell command:

| src/emacs -Q -batch -eval '(progn (setenv "TZ" "Asia/Kolkata") (print
| (encode-time 44 42 6 15 2 2015 0 nil 0)))'

| What output do you get?  Here's what I get on Fedora 21 x86-64, which seems correct:

| oldtz=Asia/Kolkata tz=XXX-0:00:00 oldTZ=Asia/Kolkata TZ=XXX-0:00:00
| 2015-02-15 06:42:44 -1 -> 2015-02-15 06:42:44 0 = 1423982564

| Assuming you get different output, can you debug Emacs with GDB to
| send us more details about what's going wrong?  If not, can you give
| me access to a FreeBSD 10.1 amd64 machine like yours?

Hi,

When I looked into this before filing this bug report, from what I noticed
that it's not using libc's `mktime' function, unlike what you seem to
indicate. I'm not sure quite why it's doing that when libc provided mktime
works just fine, as evident by output of attached program:

--8<---------------cut here---------------start------------->8---
% ./gmtime
Staying at localtime zone
Time (in seconds): 1423962764
Updated environment
Switching to UTC
Time (in seconds): 1423982564
Didn't update environment
Switching to UTC+1
Time (in seconds): 1423978964
Didn't update environment
Switching to UTC+3
Time (in seconds): 1423971764
--8<---------------cut here---------------end--------------->8---

--8<---------------cut here---------------start------------->8---
>>> print gmtime(1423962764)
time.struct_time(tm_year=2015, tm_mon=2, tm_mday=15, tm_hour=1, tm_min=12, tm_sec=44, tm_wday=6, tm_yday=46, tm_isdst=0)
>>> print gmtime(1423982564)
time.struct_time(tm_year=2015, tm_mon=2, tm_mday=15, tm_hour=6, tm_min=42, tm_sec=44, tm_wday=6, tm_yday=46, tm_isdst=0)
>>> print gmtime(1423978964)
time.struct_time(tm_year=2015, tm_mon=2, tm_mday=15, tm_hour=5, tm_min=42, tm_sec=44, tm_wday=6, tm_yday=46, tm_isdst=0)
>>> print gmtime(1423971764)
time.struct_time(tm_year=2015, tm_mon=2, tm_mday=15, tm_hour=3, tm_min=42, tm_sec=44, tm_wday=6, tm_yday=46, tm_isdst=0)
--8<---------------cut here---------------end--------------->8---

The built-in mktime implementation (__mktime_internal) in Emacs sources don't
seem to take into account timezone offsets. I might be completely wrong here,
but the code seemed to be doing it.

I'll get back to you with the output of your command-line from patched Emacs
in few, but the results of my past investigation were handy so I've attached
them.

HTH
-- 
Ashish SHUKLA

“"Intellectual Property" is nowhere near as valuable as "Intellect"” ("Ion-Mihai Tetcu")

Sent from my Emacs

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#include <time.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define BUFSIZE 256

void
settz(const char* tz)
{
	static char *tzvalbuf;
	static size_t tzvalbufsize;

	if( tzvalbufsize <= 3 + strlen(tz)) {
		tzvalbuf = malloc(tzvalbufsize = BUFSIZE);
		snprintf( tzvalbuf, BUFSIZE, "TZ=%s", tz );
		putenv( tzvalbuf );
		puts( "Updated environment" );
	} else {
		puts( "Didn't update environment" );
		snprintf( tzvalbuf, BUFSIZE, "TZ=%s", tz );
	}
	tzset();
}

int
main()
{
	struct tm t = {
		.tm_sec = 44,
		.tm_min = 42,
		.tm_hour = 6,
		.tm_mday = 15,
		.tm_mon = 2 - 1,
		.tm_year = 2015 - 1900,
		.tm_isdst = -1,
	};
	time_t val;

	puts( "Staying at localtime zone" );
	val = mktime( &t );
	printf( "Time (in seconds): %ld\n", val );
	settz( "TZ=XXX-0:00:00" );
	puts( "Switching to UTC" );
	val = mktime( &t );
	printf( "Time (in seconds): %ld\n", val );
	settz( "TZ=XXX-1:00:00" );
	puts( "Switching to UTC+1" );
	val = mktime( &t );
	printf( "Time (in seconds): %ld\n", val );
	settz( "TZ=XXX-3:00:00" );
	puts( "Switching to UTC+3" );
	val = mktime( &t );
	printf( "Time (in seconds): %ld\n", val );

	return 0;
}

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