doc/timetable: Document `normalise` fractional behaviour

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

diff --git a/luatz/timetable.lua b/luatz/timetable.lua
index 8c44f2f6897ebf5d17db65aebcca1b2ea347cf7f..fc89fcaec5c7271d6756ed4c3ff0429e01ff7280 100644 (file)
--- a/luatz/timetable.lua
+++ b/luatz/timetable.lua
@@ -1,3 +1,4 @@
+local strftime = require "luatz.strftime".strftime

 local strformat = string.format
 local floor = math.floor
 local function idiv ( n , d )
 local strformat = string.format
 local floor = math.floor
 local function idiv ( n , d )


@@ -11,9 +12,17 @@ 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 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 )
 
 local function is_leap ( y )

-       return (y % 4) == 0 and (y % 100) ~= 0 or (y % 400) == 0
+       if (y % 4) ~= 0 then
+               return false
+       elseif (y % 100) ~= 0 then
+               return true
+       else
+               return (y % 400) == 0
+       end

 end
 
 local function year_length ( y )
 end
 
 local function year_length ( y )


@@ -32,19 +41,6 @@ local function leap_years_since ( year )
        return idiv ( year , 4 ) - idiv ( year , 100 ) + idiv ( year , 400 )
 end
 
        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
 local function day_of_year ( day , month , year )
        local yday = months_to_days_cumulative [ month ]
        if month > 2 and is_leap ( year ) then


@@ -53,11 +49,21 @@ local function day_of_year ( day , month , year )
        return yday + day
 end
 
        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 borrow ( tens , units , base )
+       local frac = tens % 1
+       units = units + frac * base
+       tens = tens - frac
+       return tens , units

 end
 
 end
 

-local function increment ( tens , units , base )
+local function carry ( tens , units , base )

        if units >= base then
                tens  = tens + idiv ( units , base )
                units = units % base
        if units >= base then
                tens  = tens + idiv ( units , base )
                units = units % base


@@ -70,32 +76,50 @@ end
 
 -- Modify parameters so they all fit within the "normal" range
 local function normalise ( year , month , day , hour , min , sec )
 
 -- 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?
-       hour , min  = increment ( hour , min  , 60 )
-       day  , hour = increment ( day  , hour , 24 )
-
-       while day <= 0 do
+       -- `month` and `day` start from 1, need -1 and +1 so it works modulo
+       month , day = month - 1 , day - 1
+
+       -- Convert everything (except seconds) to an integer
+       -- by propagating fractional components down.
+       year  , month = borrow ( year  , month , 12 )
+       -- Carry from month to year first, so we get month length correct in next line around leap years
+       year  , month = carry ( year , month , 12 )
+       month , day   = borrow ( month , day   , month_length ( floor ( month + 1 ) , year ) )
+       day   , hour  = borrow ( day   , hour  , 24 )
+       hour  , min   = borrow ( hour  , min   , 60 )
+       min   , sec   = borrow ( min   , sec   , 60 )
+
+       -- Propagate out of range values up
+       -- e.g. if `min` is 70, `hour` increments by 1 and `min` becomes 10
+       -- This has to happen for all columns after borrowing, as lower radixes may be pushed out of range
+       min   , sec   = carry ( min   , sec   , 60 ) -- TODO: consider leap seconds?
+       hour  , min   = carry ( hour  , min   , 60 )
+       day   , hour  = carry ( day   , hour  , 24 )
+       -- Ensure `day` is not underflowed
+       -- Add a whole year of days at a time, this is later resolved by adding months
+       -- TODO[OPTIMIZE]: This could be slow if `day` is far out of range
+       while day < 0 do

                year = year - 1
                day  = day + year_length ( year )
        end
                year = year - 1
                day  = day + year_length ( year )
        end

+       year , month = carry ( year , month , 12 )

 
 

-       -- Lua months start from 1, need -1 and +1 around this increment
-       month = month - 1
-       year , month = increment ( year , month , 12 )
-       month = month + 1
-
-       -- This could potentially be slow if `day` is very large
+       -- TODO[OPTIMIZE]: This could potentially be slow if `day` is very large

        while true do
        while true do

-               local i = month_length ( month , year )
-               if day <= i then break end
+               local i = month_length ( month + 1 , year )
+               if day < i then break end

                day = day - i
                month = month + 1
                day = day - i
                month = month + 1

-               if month > 12 then
-                       month = 1
+               if month >= 12 then
+                       month = 0

                        year = year + 1
                end
        end
 
                        year = year + 1
                end
        end
 

+       -- Now we can place `day` and `month` back in their normal ranges
+       -- e.g. month as 1-12 instead of 0-11
+       month , day = month + 1 , day + 1
+

        return year , month , day , hour , min , sec
 end
 
        return year , month , day , hour , min , sec
 end
 


@@ -135,12 +159,8 @@ function timetable_methods:normalise ( )
        self.day   = day
        self.month = month
        self.year  = year
        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
 
        return self
 end


@@ -155,6 +175,10 @@ function timetable_methods:rfc_3339 ( )
        return strformat ( "%04u-%02u-%02uT%02u:%02u:%06.3f" , self:unpack ( ) )
 end
 
        return strformat ( "%04u-%02u-%02uT%02u:%02u:%06.3f" , self:unpack ( ) )
 end
 

+function timetable_methods:strftime ( format_string )
+       return strftime ( format_string , self )
+end
+

 local timetable_mt
 
 local function coerce_arg ( t )
 local timetable_mt
 
 local function coerce_arg ( t )


@@ -168,10 +192,13 @@ timetable_mt = {
        __index    = timetable_methods ;
        __tostring = timetable_methods.rfc_3339 ;
        __eq = function ( a , b )
        __index    = timetable_methods ;
        __tostring = timetable_methods.rfc_3339 ;
        __eq = function ( a , b )

-               return coerce_arg ( a ) == coerce_arg ( b )
+               return a:timestamp ( ) == b:timestamp ( )

        end ;
        __lt = function ( a , b )
        end ;
        __lt = function ( a , b )

-               return coerce_arg ( a ) < coerce_arg ( b )
+               return a:timestamp ( ) < b:timestamp ( )
+       end ;
+       __sub = function ( a , b )
+               return coerce_arg ( a ) - coerce_arg ( b )

        end ;
 }
 
        end ;
 }
 


@@ -197,11 +224,16 @@ function timetable_methods:clone ( )
 end
 
 local function new_from_timestamp ( ts )
 end
 
 local function new_from_timestamp ( ts )

-       return new_timetable ( 1970 , 1 , 1 , 0 , 0 , ts )
+       if type ( ts ) ~= "number" then
+               error ( "bad argument #1 to 'new_from_timestamp' (number expected, got " .. type ( ts ) .. ")" , 2 )
+       end
+       return new_timetable ( 1970 , 1 , 1 , 0 , 0 , ts ):normalise ( )

 end
 
 return {
 end
 
 return {

-       doomsday  = doomsday ;
+       is_leap = is_leap ;
+       day_of_year = day_of_year ;
+       day_of_week = day_of_week ;

        normalise = normalise ;
        timestamp = timestamp ;
 
        normalise = normalise ;
        timestamp = timestamp ;