ezic:local_to_utc/2 added, working.

in the case of ambiguous timezones, an "ambiguous_zone" error is thrown with the two valid zones.
if no zones existed for the given local time (i.e. DST eliminated the hour in question), a "no_zone" error is thrown.
otherwise, the date is returned

src/ezic.erl

@@ -4,6 +4,7 @@
 -export([
 	 localtime/1
 	 , utc_to_local/2
+	 , local_to_utc/2
 	 , next_timechange/1
 	 , next_timechange_after/2
 	]).
@@ -44,6 +45,16 @@ utc_to_local(UTCDatetime, TzName) ->
       , DSTOffset).
     
 
+local_to_utc(LocalDatetime, TzName) ->
+    NormalDatetime= ezic_date:normalize(LocalDatetime, w),
+    #flatzone{offset=Offset, dstoffset=DSTOffset}= ezic_db:flatzone(NormalDatetime, TzName),
+    
+    ezic_date:add_offset(
+      ezic_date:add_offset(
+	LocalDatetime
+	, Offset, {0,0,0})
+      , DSTOffset, {0,0,0}).
+	    
 
 
 next_timechange(TzName) ->

src/ezic_db.erl

@@ -68,9 +68,18 @@ flatzone(Date, TzName) ->
 				 , ezic_flatten:contains_date(Fz, Date)]),
 		qlc:e(Q)
 	end,
-    {atomic, [FlatZone]}= mnesia:transaction(F),
-    FlatZone.
-    
+    {atomic, FlatZones}= mnesia:transaction(F),
+
+    case length(FlatZones) of
+	1 ->
+	    hd(FlatZones);
+	2 ->
+	    erlang:error(ambiguous_zone, FlatZones);
+	0 ->
+	    erlang:error(no_zone);
+	_ ->
+	    erlang:error(should_not_happen, {FlatZones, Date, TzName})
+    end.
     
 
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