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alerted to buginess in README. added notes & zic reference. removed local_to_utc conversion for now.

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Time comparisons are patently wrong. They do not consider s/w/u/g/z time modifiers, so the comparisons can be off by hours. At least 24 hours within any time or zone change, ezic will give unreliable results.
I think a solution can involve "flattening" the data, starting from the earliest time possible for each zone/rule, going forward.
There exist ambiguous local times for zones and rules. For example, on Nov 7th, in Los Angeles, the times from 1:00:00am to 1:59:59am were repeated, once for PDT and once for PST. Given a local time in that zone between those times, we cannot determine what UTC time is unambiguously. Similar for Zone transitions where fall-back occurs.
This commit is contained in:
aj
2010-11-07 12:52:51 -08:00
parent 4d95017b7f
commit 329f699e51
7 changed files with 609 additions and 51 deletions
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20
README.md
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@@ -4,6 +4,18 @@ ezic is a set of erlang utilities for the Olsen timezone database files. See the
Status
------
2010.11.07
* The time comparisons don't consider time relativity, so they're plain wrong. Within at least 24 hours of timechange or zone change, the results cannot be trusted.
2010.11.04
* ezic is "apparently functional". It has been tested very lightly, a bit by unit tests, but mostly by inspection. It's probably not fit for production use.
License
-------
@@ -18,14 +30,6 @@ To maintain ezic's status as a public domain work, all contributions must also b
Status
------
2010.11.04
* ezic is "apparently functional". It has been tested very lightly, a bit by unit tests, but mostly by inspection. It's probably not fit for production use.
API
---

204
notes/local_to_utc.svg Normal file
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313
notes/zic.8.txt Normal file
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NAME
zic - time zone compiler
SYNOPSIS
zic [ --version ] [ -v ] [ -d directory ] [ -l localtime ] [
-p posixrules ] [ -L leapsecondfilename ] [ -s ] [ -y
command ] [ filename ... ]
DESCRIPTION
Zic reads text from the file(s) named on the command line
and creates the time conversion information files specified
in this input. If a filename is -, the standard input is
read.
These options are available:
--version
Output version information and exit.
-d directory
Create time conversion information files in the named
directory rather than in the standard directory named
below.
-l timezone
Use the given time zone as local time. Zic will act as
if the input contained a link line of the form
Link timezone localtime
-p timezone
Use the given time zone's rules when handling POSIX-
format time zone environment variables. Zic will act
as if the input contained a link line of the form
Link timezone posixrules
-L leapsecondfilename
Read leap second information from the file with the
given name. If this option is not used, no leap second
information appears in output files.
-v Complain if a year that appears in a data file is
outside the range of years representable by time(2)
values. Also complain if a time of 24:00 (which cannot
be handled by pre-1998 versions of zic) appears in the
input.
-s Limit time values stored in output files to values that
are the same whether they're taken to be signed or
unsigned. You can use this option to generate SVVS-
compatible files.
-y command
Use the given command rather than yearistype when
checking year types (see below).
Input lines are made up of fields. Fields are separated
from one another by any number of white space characters.
Leading and trailing white space on input lines is ignored.
An unquoted sharp character (#) in the input introduces a
comment which extends to the end of the line the sharp
character appears on. White space characters and sharp
characters may be enclosed in double quotes (") if they're
to be used as part of a field. Any line that is blank
(after comment stripping) is ignored. Non-blank lines are
expected to be of one of three types: rule lines, zone
lines, and link lines.
Names (such as month names) must be in English and are case
insensitive. Abbreviations, if used, must be unambiguous in
context.
A rule line has the form
Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S
For example:
Rule US 1967 1973 - Apr lastSun 2:00 1:00 D
The fields that make up a rule line are:
NAME Gives the (arbitrary) name of the set of rules this
rule is part of.
FROM Gives the first year in which the rule applies. Any
integer year can be supplied; the Gregorian calendar
is assumed. The word minimum (or an abbreviation)
means the minimum year representable as an integer.
The word maximum (or an abbreviation) means the
maximum year representable as an integer. Rules can
describe times that are not representable as time
values, with the unrepresentable times ignored; this
allows rules to be portable among hosts with
differing time value types.
TO Gives the final year in which the rule applies. In
addition to minimum and maximum (as above), the word
only (or an abbreviation) may be used to repeat the
value of the FROM field.
TYPE Gives the type of year in which the rule applies.
If TYPE is - then the rule applies in all years
between FROM and TO inclusive. If TYPE is something
else, then zic executes the command
yearistype year type
to check the type of a year: an exit status of zero
is taken to mean that the year is of the given type;
an exit status of one is taken to mean that the year
is not of the given type.
IN Names the month in which the rule takes effect.
Month names may be abbreviated.
ON Gives the day on which the rule takes effect.
Recognized forms include:
5 the fifth of the month
lastSun the last Sunday in the month
lastMon the last Monday in the month
Sun>=8 first Sunday on or after the eighth
Sun<=25 last Sunday on or before the 25th
Names of days of the week may be abbreviated or
spelled out in full. Note that there must be no
spaces within the ON field.
AT Gives the time of day at which the rule takes
effect. Recognized forms include:
2 time in hours
2:00 time in hours and minutes
15:00 24-hour format time (for times after noon)
1:28:14 time in hours, minutes, and seconds
- equivalent to 0
where hour 0 is midnight at the start of the day,
and hour 24 is midnight at the end of the day. Any
of these forms may be followed by the letter w if
the given time is local "wall clock" time, s if the
given time is local "standard" time, or u (or g or
z) if the given time is universal time; in the
absence of an indicator, wall clock time is assumed.
SAVE Gives the amount of time to be added to local
standard time when the rule is in effect. This
field has the same format as the AT field (although,
of course, the w and s suffixes are not used).
LETTER/S
Gives the "variable part" (for example, the "S" or
"D" in "EST" or "EDT") of time zone abbreviations to
be used when this rule is in effect. If this field
is -, the variable part is null.
A zone line has the form
Zone NAME GMTOFF RULES/SAVE FORMAT [UNTILYEAR [MONTH [DAY [TIME]]]]
For example:
Zone Australia/Adelaide 9:30 Aus CST 1971 Oct 31 2:00
The fields that make up a zone line are:
NAME The name of the time zone. This is the name used in
creating the time conversion information file for the
zone.
GMTOFF
The amount of time to add to UTC to get standard time
in this zone. This field has the same format as the
AT and SAVE fields of rule lines; begin the field with
a minus sign if time must be subtracted from UTC.
RULES/SAVE
The name of the rule(s) that apply in the time zone
or, alternately, an amount of time to add to local
standard time. If this field is - then standard time
always applies in the time zone.
FORMAT
The format for time zone abbreviations in this time
zone. The pair of characters %s is used to show where
the "variable part" of the time zone abbreviation
goes. Alternately, a slash (/) separates standard and
daylight abbreviations.
UNTILYEAR [MONTH [DAY [TIME]]]
The time at which the UTC offset or the rule(s) change
for a location. It is specified as a year, a month, a
day, and a time of day. If this is specified, the
time zone information is generated from the given UTC
offset and rule change until the time specified. The
month, day, and time of day have the same format as
the IN, ON, and AT fields of a rule; trailing fields
can be omitted, and default to the earliest possible
value for the missing fields.
The next line must be a "continuation" line; this has
the same form as a zone line except that the string
"Zone" and the name are omitted, as the continuation
line will place information starting at the time
specified as the "until" information in the previous
line in the file used by the previous line.
Continuation lines may contain "until" information,
just as zone lines do, indicating that the next line
is a further continuation.
A link line has the form
Link LINK-FROM LINK-TO
For example:
Link Europe/Istanbul Asia/Istanbul
The LINK-FROM field should appear as the NAME field in some
zone line; the LINK-TO field is used as an alternate name
for that zone.
Except for continuation lines, lines may appear in any order
in the input.
Lines in the file that describes leap seconds have the
following form:
Leap YEAR MONTH DAY HH:MM:SS CORR R/S
For example:
Leap 1974 Dec 31 23:59:60 + S
The YEAR, MONTH, DAY, and HH:MM:SS fields tell when the leap
second happened. The CORR field should be "+" if a second
was added or "-" if a second was skipped. The R/S field
should be (an abbreviation of) "Stationary" if the leap
second time given by the other fields should be interpreted
as UTC or (an abbreviation of) "Rolling" if the leap second
time given by the other fields should be interpreted as
local wall clock time.
EXTENDED EXAMPLE
Here is an extended example of zic input, intended to
illustrate many of its features.
# Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S
Rule Swiss 1940 only - Nov 2 0:00 1:00 S
Rule Swiss 1940 only - Dec 31 0:00 0 -
Rule Swiss 1941 1942 - May Sun>=1 2:00 1:00 S
Rule Swiss 1941 1942 - Oct Sun>=1 0:00 0
Rule EU 1977 1980 - Apr Sun>=1 1:00u 1:00 S
Rule EU 1977 only - Sep lastSun 1:00u 0 -
Rule EU 1978 only - Oct 1 1:00u 0 -
Rule EU 1979 1995 - Sep lastSun 1:00u 0 -
Rule EU 1981 max - Mar lastSun 1:00u 1:00 S
Rule EU 1996 max - Oct lastSun 1:00u 0 -
# Zone NAME GMTOFF RULES FORMAT UNTIL
Zone Europe/Zurich 0:34:08 - LMT 1848 Sep 12
0:29:44 - BMT 1894 Jun
1:00 Swiss CE%sT 1981
1:00 EU CE%sT
Link Europe/Zurich Switzerland
In this example, the zone is named Europe/Zurich but it has
an alias as Switzerland. Zurich was 34 minutes and 8
seconds west of GMT until 1848-09-12 at 00:00, when the
offset changed to 29 minutes and 44 seconds. After
1894-06-01 at 00:00 Swiss daylight saving rules (defined
with lines beginning with "Rule Swiss") apply, and the GMT
offset became one hour. From 1981 to the present, EU
daylight saving rules have applied, and the UTC offset has
remained at one hour.
In 1940, daylight saving time applied from November 2 at
00:00 to December 31 at 00:00. In 1941 and 1942, daylight
saving time applied from the first Sunday in May at 02:00 to
the first Sunday in October at 00:00. The pre-1981 EU
daylight-saving rules have no effect here, but are included
for completeness. Since 1981, daylight saving has begun on
the last Sunday in March at 01:00 UTC. Until 1995 it ended
the last Sunday in September at 01:00 UTC, but this changed
to the last Sunday in October starting in 1996.
For purposes of display, "LMT" and "BMT" were initially
used, respectively. Since Swiss rules and later EU rules
were applied, the display name for the timezone has been CET
for standard time and CEST for daylight saving time.
NOTES
For areas with more than two types of local time, you may
need to use local standard time in the AT field of the
earliest transition time's rule to ensure that the earliest
transition time recorded in the compiled file is correct.
If, for a particular zone, a clock advance caused by the
start of daylight saving coincides with and is equal to a
clock retreat caused by a change in UTC offset, zic produces
a single transition to daylight saving at the new UTC offset
(without any change in wall clock time). To get separate
transitions use multiple zone continuation lines specifying
transition instants using universal time.
FILE
/usr/local/etc/zoneinfo standard directory used for
created files
SEE ALSO
newctime(3), tzfile(5), zdump(8)

46
src/ezic.erl
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@@ -4,8 +4,8 @@
-export([
localtime/1
, utc_to_local/2
, utc_from_local/2
, zone_convert/3
% , local_to_utc/2
% , zone_convert/3
, next_timechange/1
, next_timechange/2
]).
@@ -28,28 +28,28 @@ localtime(TzName) ->
utc_to_local(erlang:universaltime(), TzName).
utc_to_local(Datetime, TzName) ->
{ok, Zone, Rule}= current(Datetime, TzName),
SecDiff= offset(Zone, Rule),
date_add(Datetime, SecDiff).
utc_to_local(UTCDatetime, TzName) ->
{ok, Zone, Rule}= current_as_of_utc(UTCDatetime, TzName),
SecDiff= time_offset(Zone, Rule),
date_add(UTCDatetime, SecDiff).
utc_from_local(Datetime, TzName) ->
{ok, Zone, Rule}= current(Datetime, TzName),
SecDiff= offset(Zone, Rule),
date_subtract(Datetime, SecDiff).
%% local_to_utc(Datetime, TzName) ->
%% {ok, Zone, Rule}= current_as_of_local(Datetime, TzName),
%% SecDiff= time_offset(Zone, Rule),
%% date_subtract(Datetime, SecDiff).
zone_convert(Datetime, FromTimeZone, ToTimeZone) ->
UTC= utc_from_local(Datetime, FromTimeZone),
utc_to_local(UTC, ToTimeZone).
%% zone_convert(Datetime, FromTimeZone, ToTimeZone) ->
%% UTC= local_to_utc(Datetime, FromTimeZone),
%% utc_to_local(UTC, ToTimeZone).
next_timechange(TzName) ->
next_timechange(localtime(TzName), TzName).
next_timechange(erlang:universaltime(), TzName).
next_timechange(Datetime, TzName) ->
next_timechange(UtcDatetime, TzName) ->
not_done.
@@ -84,23 +84,19 @@ test() ->
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
current(Datetime, TzName) ->
Zones= ezic_db:zones(TzName),
% ?debug("All Zones: ~p", [Zones]),
CZone= ezic_zone:current(Datetime, Zones),
% ?debug("Current Zone: ~p", [CZone]),
current_as_of_utc(UTCDatetime, TzName) ->
CZone= ezic_zone:current_as_of_utc(UTCDatetime, TzName),
RuleName= CZone#zone.rule,
Rules= ezic_db:rules(RuleName),
% ?debug("All Rules: ~p", [Rules]),
CRule= ezic_rule:current(Datetime, Rules),
% ?debug("Current Rule: ~p", [CRule]),
CRule= ezic_rule:current_as_of_utc(UTCDatetime, Rules),
{ok, CZone, CRule}.
%%current_as_of_local(Datetime, TzName) ->
%% not_done.
offset(Zone, Rule) ->
time_offset(Zone, Rule) ->
OffsetSec= ezic_zone:offset_sec(Zone),
DSTSec= ezic_rule:dst_sec(Rule),
OffsetSec + DSTSec.

15
src/ezic_date.erl
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@@ -16,7 +16,8 @@
% returns the concrete date tuple for a given rule and year, irrespective of zone
% returns the date tuple for a given rule and year
% same for all timezones.
% e.g. -> {Y,M,D}
for(#rule{in=M, on={last, D}}, Y) ->
last_day_of(D, Y,M);
@@ -24,13 +25,15 @@ for(#rule{in=M, on=#tzon{day=Day, filter=Filter}}, Y) ->
first_day_limited(Day, Filter, Y,M).
% returns the date on which the last Day (sun,mon,tue,etc.) occurs in a given month/year
% same for all timezones
last_day_of(Day, Y,M) ->
LastDay= calendar:last_day_of_the_month(Y,M),
previous_day(Day, {Y,M,LastDay}).
% returns a date tuple {Y,M,D} representing the first available date, given the filter
% same for all timezones
first_day_limited(Day, {geq, N}, Y,M) ->
next_day(Day, {Y,M,N});
first_day_limited(Day, {leq, N}, Y,M) ->
@@ -38,7 +41,8 @@ first_day_limited(Day, {leq, N}, Y,M) ->
% Returns the soonest date on which Day (sun/mon/tue/etc.) occurs BEFORE the given date.
% same for all timezones
previous_day(Day, Date={Y,M,D}) ->
Daynum= day_to_num(Day),
LeqDoW= calendar:day_of_the_week(Date),
@@ -56,6 +60,8 @@ previous_day(Day, Date={Y,M,D}) ->
end.
% Returns the soonest date on which Day (sun/mon/tue/etc.) occurs AFTER the given date.
% same for all timezones
next_day(Day, Date={Y,M,D}) ->
Daynum= day_to_num(Day),
LeqDoW= calendar:day_of_the_week(Date),
@@ -115,6 +121,8 @@ compare_datetimes_normal(current, current) -> true;
compare_datetimes_normal(current, _) -> false;
compare_datetimes_normal(_,current) -> true;
% @bug this is not true if the times are from different time zones
% @todo check types for D1 and D2
compare_datetimes_normal({D1, _}, {D2, _}) when D1 < D2 ->
true;
compare_datetimes_normal({D1, _}, {D2, _}) when D1 > D2 ->
@@ -144,6 +152,7 @@ normalize(only) -> only;
normalize(maximum) -> maximum;
normalize(minimum) -> minimum;
normalize(Y) when is_integer(Y) ->
{{Y,1,1}, #tztime{}};
normalize(Date={_,_,D}) when is_integer(D) ->

14
src/ezic_rule.erl
View File

@@ -2,7 +2,7 @@
-include("include/ezic.hrl").
-export([current/2, relevant/2, sort/2]).
-export([current/2, current_set/2, sort/2]).
-export([from_time/1, dst_sec/1]).
@@ -10,9 +10,9 @@
current(_, []) ->
none;
current(Now, Rules) ->
RelevantRules= lists:filter(fun(R)-> relevant(Now, R) end, Rules),
% ?debug("RelevantRules: ~p", [RelevantRules]),
SRules= lists:sort(fun sort/2, RelevantRules),
Current_SetRules= lists:filter(fun(R)-> current_set(Now, R) end, Rules),
% ?debug("Current_SetRules: ~p", [Current_SetRules]),
SRules= lists:sort(fun sort/2, Current_SetRules),
CRule= choose_rule(SRules),
CRule.
@@ -27,15 +27,15 @@ sort(R1, R2) ->
relevant(Now, Rule=#rule{from=F, to=T}) ->
current_set(Now, Rule=#rule{from=F, to=T}) ->
{{Y,_,_},_} = Now,
case ezic_date:date_between(Y, {F,T}) of
false -> false;
true -> relevant2(Now, Rule)
true -> current_set2(Now, Rule)
end.
relevant2(Now, #rule{in=Month, on=Day, at=Time}) ->
current_set2(Now, #rule{in=Month, on=Day, at=Time}) ->
{{Y,_,_},_} = Now,
RTime= {{Y, Month, Day}, Time},
ezic_date:compare_datetimes(RTime, Now).

48
src/ezic_zone.erl
View File

@@ -1,16 +1,45 @@
-module(ezic_zone).
-include("include/ezic.hrl").
-export([current/2, sort/2, revsort/2, offset_sec/1]).
-export([
current/1
, current_as_of_utc/2
, sort/2
, revsort/2
, offset_sec/1
]).
current(_, []) ->
current(TzName) ->
current_as_of_utc(erlang:universaltime(), TzName).
current_as_of_utc(UTCDatetime, TzName) ->
Zones= ezic_db:zones(TzName),
get_zone_utc(UTCDatetime, Zones).
%%current_as_of_local(_Datetime, _TzName) ->
%% not_done.
get_zone_utc(_, []) ->
erlang:error(no_current);
current(Now, Zones) ->
get_zone_utc(UTCDatetime, Zones) ->
SortedZones= lists:sort(fun revsort/2, Zones),
% ?debug("SortedZones: ~p", [SortedZones]),
[CZone|_]= lists:dropwhile(fun(SZ)-> older_zone(SZ, Now) end, SortedZones),
CZone.
%% [CZone|_]= lists:dropwhile(fun(SZ)-> older_zone_utc(SZ, UTCDatetime) end, SortedZones),
%% CZone.
%% begin with GMT offset.
%% foreach rule (oldest first)
%% see whether until=(standard|wall|utc) time
%%
not_done.
@@ -20,8 +49,11 @@ sort(#zone{until=U1}, #zone{until=U2}) ->
revsort(Z1=#zone{}, Z2=#zone{}) ->
not sort(Z1, Z2).
older_zone(#zone{until=Until}, Now) ->
ezic_date:compare_datetimes(Until, Now).
% @bug doesn't normalize times. Times are self-relative (to standard time), and Now may come from any timezone unless we're careful about that.
older_zone(#zone{until=Until}, UTCDatetime) ->
ezic_date:compare_datetimes(Until, UTCDatetime).