From 12a8febabf1d5fe90d7c623377507d28a0f0fc80 Mon Sep 17 00:00:00 2001
From: daurnimator <quae@daurnimator.com>
Date: Mon, 6 Jan 2014 15:56:55 -0500
Subject: [PATCH] luatz/timetable: Use sakamoto's algorithm instead of doomsday
algorithm
---
luatz/timetable.lua | 33 +++++++++++----------------------
spec/timetable_spec.lua | 13 +++----------
2 files changed, 14 insertions(+), 32 deletions(-)
diff --git a/luatz/timetable.lua b/luatz/timetable.lua
index 8c44f2f..e1649a0 100644
--- 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 )
@@ -135,12 +127,8 @@ function timetable_methods:normalise ( )
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
@@ -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 ;
diff --git a/spec/timetable_spec.lua b/spec/timetable_spec.lua
index 4cadbbc..c81308e 100644
--- a/spec/timetable_spec.lua
+++ b/spec/timetable_spec.lua
@@ -1,16 +1,6 @@
describe ( "Time table library" , function ( )
local timetable = require "luatz.timetable"
- it ( "Doomsday calculation" , function ( )
- local doomsday = timetable.doomsday
-
- -- Doomsday in Gregorian calendar for 2013 is Thursday.
- assert.are.same ( 5 , doomsday(2013) )
-
- assert.are.same ( 3 , doomsday(1967) )
- assert.are.same ( 5 , doomsday(1968) )
- end )
-
local function native_normalise ( year , month , day )
return os.date("*t",os.time{
year = year ;
@@ -35,6 +25,9 @@ describe ( "Time table library" , function ( )
assert_same_wday ( 2013 , 7 , 27 )
assert_same_wday ( 2013 , 7 , 28 )
assert_same_wday ( 2013 , 7 , 29 )
+ assert_same_wday ( 2014 , 1 , 1 )
+ assert_same_wday ( 2014 , 1 , 6 )
+ assert_same_wday ( 2016 , 2 , 28 )
end )
local function native_timestamp ( year , month , day )
--
2.39.5