[fpc-devel] FPC V3.0.0 LocalTimeToUniversal() error

[wkitty42 at windstream.net]

On 06/27/2016 11:55 PM, Russ Davies wrote:
> Hi,
>
> My local time zone is GMT +2, and have noticed that with V3.0.0, that the
> LocalTimeToUniversal() function is adding the offset instead of subtracting it:

i get the same over here...

> Comparing dateutil.inc for both versions, in functions UniversalTimeToLocal()
> and LocalTimeToUniversal() the signs of the offsets have been changed

yeah, it does look backwards... i'm currently -0400 and the program says

2016 Jun 28  03:06:20 -0400
myuser at mymachine:~/development/projects/misc$ ./timetest.2.6.4
Offset     :240
Local Time :03:06:21
UTC        :07:06:21

2016 Jun 28  03:06:21 -0400
myuser at mymachine:~/development/projects/misc$ ./timetest.3.0.0
Offset     :240
Local Time :03:06:22
UTC        :23:06:22


i don't understand why LocalTimeToUniversal() isn't more simple... subtracting a 
negative is the same as adding the positive and subtracting a positive is, well, 
subtracting... it looks like they were trying to catch and protect from division 
by zero when the offset is 0 or there is no offset which results in the offset 
being 0... the following should work and be easier to follow...


Function LocalTimeToUniversal(LT: TDateTime;TZOffset: Integer): TDateTime;

begin
   if (TZOffset <> 0) then
     Result := LT - EncodeTime(TZOffset div 60, TZOffset mod 60, 0, 0)
   else
     Result := LT;
end;


at least they're not trying to determine which timezone specification is in 
use... the two that i know of are backwards from each other... using the 
standard (POSIX??) form, i'm EST5EDT (-0500 and -0400) but using the other form 
(America/New York or Etc/GMT-5 ???) i'm 0500 and 0400 which means that the 
formula for the standard form is subtracting whereas the other one is adding 
when going from local time to GMT time... yeah, it gets really twisted and using 
the wrong form, while correct for your area, can result in time being off by 12 
hours (IIRC)...

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