www.digitalmars.com         C & C++   DMDScript  

digitalmars.D - std.date time problem

reply Regan Heath <regan netmail.co.nz> writes:
I think this is a bug, but I can't be sure.

[time.d]
import std.stdio, std.date;

void main()
{
	d_time now = UTCtoLocalTime(getUTCtime());
	writefln("%s", toTimeString(now));
}

dmd -run time.d
10:54:42 GMT+0100

time /t
09:55

I am in London so at GMT, but it's summer so we're at +0100 currently 
(aka BST).  It seems std.date adds an extra hour?

Regan
Aug 21 2007
next sibling parent reply Deewiant <deewiant.doesnotlike.spam gmail.com> writes:
Regan Heath wrote:

 I think this is a bug, but I can't be sure.
 
 [time.d]
 import std.stdio, std.date;
 
 void main()
 {
     d_time now = UTCtoLocalTime(getUTCtime());
     writefln("%s", toTimeString(now));
 }
 
 dmd -run time.d
 10:54:42 GMT+0100
 
 time /t
 09:55
 
 I am in London so at GMT, but it's summer so we're at +0100 currently
 (aka BST).  It seems std.date adds an extra hour?
 



Yep, it's buggy. std.date does essentially the following in getLocalTZA() on
Windows (shortened to pseudocode):

TIME_ZONE_INFORMATION tzi;
GetTimeZoneInformation(&tzi);

if (unknown time zone || in standard time || in daylight savings time)
	return -(tzi.Bias + tzi.StandardBias) * 60 * TicksPerSecond;
else
	return 0; // error

Microsoft documents at http://msdn2.microsoft.com/en-us/library/ms725481.aspx
that:

- "Bias" is "[t]he current bias for local time translation on this computer, in
minutes" and "UTC = local time + bias".

- "StandardBias" is "[t]he bias value to be used during local time translations
that occur during standard time."

- "DaylightBias" (not used in std.date) is "[t]he bias value to be used during
local time translations that occur during daylight saving time."

That is, UTC = local time + Bias + StandardBias, or UTC = local time + Bias +
DaylightBias, depending on whether DST is active or not.

However, Phobos uses StandardBias in all cases. It should use DaylightBias if
GetTimeZoneInformation returns TIME_ZONE_ID_DAYLIGHT.

In London, I presume that Bias is 0, StandardBias is 0, and DaylightBias is -60,
which is why std.date is wrong.

-- 
Remove ".doesnotlike.spam" from the mail address.
Aug 21 2007
parent Regan Heath <regan netmail.co.nz> writes:
Deewiant wrote:

 Regan Heath wrote:

 I think this is a bug, but I can't be sure.

 [time.d]
 import std.stdio, std.date;

 void main()
 {
     d_time now = UTCtoLocalTime(getUTCtime());
     writefln("%s", toTimeString(now));
 }

 dmd -run time.d
 10:54:42 GMT+0100

 time /t
 09:55

 I am in London so at GMT, but it's summer so we're at +0100 currently
 (aka BST).  It seems std.date adds an extra hour?



 Yep, it's buggy. std.date does essentially the following in getLocalTZA() on
 Windows (shortened to pseudocode):
 
 TIME_ZONE_INFORMATION tzi;
 GetTimeZoneInformation(&tzi);
 
 if (unknown time zone || in standard time || in daylight savings time)
 	return -(tzi.Bias + tzi.StandardBias) * 60 * TicksPerSecond;
 else
 	return 0; // error
 
 Microsoft documents at http://msdn2.microsoft.com/en-us/library/ms725481.aspx
that:
 
 - "Bias" is "[t]he current bias for local time translation on this computer, in
 minutes" and "UTC = local time + bias".
 
 - "StandardBias" is "[t]he bias value to be used during local time translations
 that occur during standard time."
 
 - "DaylightBias" (not used in std.date) is "[t]he bias value to be used during
 local time translations that occur during daylight saving time."
 
 That is, UTC = local time + Bias + StandardBias, or UTC = local time + Bias +
 DaylightBias, depending on whether DST is active or not.
 
 However, Phobos uses StandardBias in all cases. It should use DaylightBias if
 GetTimeZoneInformation returns TIME_ZONE_ID_DAYLIGHT.
 
 In London, I presume that Bias is 0, StandardBias is 0, and DaylightBias is
-60,
 which is why std.date is wrong.



Thanks, I'm going to post this to bugzilla.

Regan
Aug 21 2007
prev sibling parent Deewiant <deewiant.doesnotlike.spam gmail.com> writes:
Regan Heath wrote:

 I think this is a bug, but I can't be sure.



I filed Issue 1436 in the 'Zilla.

(I thought I already had, as I ran into this myself a few weeks ago. Good thing
that you reminded me. <g>)

-- 
Remove ".doesnotlike.spam" from the mail address.
Aug 21 2007