luatz/timetable: Use sakamoto's algorithm instead of doomsday algorithm

[etc/awesome.git] / luatz / timetable.lua

diff --git a/luatz/timetable.lua b/luatz/timetable.lua
index 3b3b2ed89c1205a6abf4099d7f25f6a2f8802a65..e1649a0239517c4c15bb31ca3b3191216110be1e 100644 (file)
--- a/luatz/timetable.lua
+++ b/luatz/timetable.lua
@@ -11,6 +11,8 @@ local months_to_days_cumulative = { 0 }
 for i = 2, 12 do
        months_to_days_cumulative [ i ] = months_to_days_cumulative [ i-1 ] + mon_lengths [ i-1 ]
 end
+-- For Sakamoto's Algorithm (day of week)
+local sakamoto = {0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4};
 
 local function is_leap ( y )
        return (y % 4) == 0 and (y % 100) ~= 0 or (y % 400) == 0
@@ -32,19 +34,6 @@ local function leap_years_since ( year )
        return idiv ( year , 4 ) - idiv ( year , 100 ) + idiv ( year , 400 )
 end
 
-local function doomsday ( year )
-       return ( 3 -- Tuesday
-               - 1 + year + leap_years_since ( year ) )
-               % 7 + 1
-end
-local doomsday_cache = setmetatable ( { } , {
-       __index = function ( cache , year )
-               local d = doomsday ( year )
-               cache [ year ] = d
-               return d
-       end ;
-} )
-
 local function day_of_year ( day , month , year )
        local yday = months_to_days_cumulative [ month ]
        if month > 2 and is_leap ( year ) then
@@ -53,8 +42,11 @@ local function day_of_year ( day , month , year )
        return yday + day
 end
 
-local function day_of_week ( yday , year )
-       return ( yday - doomsday_cache [ year ] - 1 ) % 7 + 1
+local function day_of_week ( day , month , year )
+       if month < 3 then
+               year = year - 1
+       end
+       return ( year + leap_years_since ( year ) + sakamoto[month] + day ) % 7 + 1
 end
 
 local function increment ( tens , units , base )
@@ -68,17 +60,6 @@ local function increment ( tens , units , base )
        return tens , units
 end
 
-local function unpack_tm ( tm )
-       return assert ( tm.year  , "year required" ) ,
-               assert ( tm.month , "month required" ) ,
-               assert ( tm.day   , "day required" ) ,
-               tm.hour or 12 ,
-               tm.min  or 0 ,
-               tm.sec  or 0 ,
-               tm.yday ,
-               tm.wday
-end
-
 -- Modify parameters so they all fit within the "normal" range
 local function normalise ( year , month , day , hour , min , sec )
        min  , sec  = increment ( min  , sec  , 60 ) -- TODO: consider leap seconds?
@@ -128,31 +109,38 @@ end
 
 local timetable_methods = { }
 
+function timetable_methods:unpack ( )
+       return assert ( self.year  , "year required" ) ,
+               assert ( self.month , "month required" ) ,
+               assert ( self.day   , "day required" ) ,
+               self.hour or 12 ,
+               self.min  or 0 ,
+               self.sec  or 0 ,
+               self.yday ,
+               self.wday
+end
+
 function timetable_methods:normalise ( )
        local year , month , day
-       year , month , day , self.hour , self.min , self.sec = normalise ( unpack_tm ( self ) )
+       year , month , day , self.hour , self.min , self.sec = normalise ( self:unpack ( ) )
 
        self.day   = day
        self.month = month
        self.year  = year
-
-       local yday = day_of_year ( day , month , year )
-       local wday = day_of_week ( yday , year )
-
-       self.yday = yday
-       self.wday = wday
+       self.yday  = day_of_year ( day , month , year )
+       self.wday  = day_of_week ( day , month , year )
 
        return self
 end
 timetable_methods.normalize = timetable_methods.normalise -- American English
 
 function timetable_methods:timestamp ( )
-       return timestamp ( unpack_tm ( self ) )
+       return timestamp ( self:unpack ( ) )
 end
 
 function timetable_methods:rfc_3339 ( )
-       -- %06.4g gives 3 (=6-4+1) digits after decimal
-       return strformat ( "%04u-%02u-%02uT%02u:%02u:%06.4g" , unpack_tm ( self ) )
+       -- %06.3f gives 3 (=6-3) digits after decimal
+       return strformat ( "%04u-%02u-%02uT%02u:%02u:%06.3f" , self:unpack ( ) )
 end
 
 local timetable_mt
@@ -193,7 +181,7 @@ local function new_timetable ( year , month , day , hour , min , sec , yday , wd
 end
 
 function timetable_methods:clone ( )
-       return new_timetable ( unpack_tm ( self ) )
+       return new_timetable ( self:unpack ( ) )
 end
 
 local function new_from_timestamp ( ts )
@@ -201,7 +189,8 @@ local function new_from_timestamp ( ts )
 end
 
 return {
-       doomsday  = doomsday ;
+       day_of_year = day_of_year ;
+       day_of_week = day_of_week ;
        normalise = normalise ;
        timestamp = timestamp ;