X-Git-Url: https://git.madduck.net/etc/awesome.git/blobdiff_plain/2d6b75a796ed12acc8aecf427d2eda1ba9b53b7d..b810c29ea3652ed987ae54eb56baa79bf24311af:/luatz/timetable.lua

diff --git a/luatz/timetable.lua b/luatz/timetable.lua
index 318bb63..1a304e2 100644
--- a/luatz/timetable.lua
+++ b/luatz/timetable.lua
@@ -1,197 +1,254 @@
+local strftime = require "luatz.strftime".strftime
 local strformat = string.format
 local floor = math.floor
-local function idiv ( n , d )
-	return floor ( n / d )
+local idiv do
+	-- Try and use actual integer division when available (Lua 5.3+)
+	local idiv_loader = (loadstring or load)([[return function(n,d) return n//d end]], "idiv") -- luacheck: ignore 113
+	if idiv_loader then
+		idiv = idiv_loader()
+	else
+		idiv = function(n, d)
+			return floor(n/d)
+		end
+	end
 end
 
 
-local mon_lengths = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }
+local mon_lengths = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
 -- Number of days in year until start of month; not corrected for leap years
-local months_to_days_cumulative = { 0 }
+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 ]
+	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
-end
-
-local function year_length ( y )
-	return is_leap ( y ) and 366 or 365
+local function is_leap(y)
+	if (y % 4) ~= 0 then
+		return false
+	elseif (y % 100) ~= 0 then
+		return true
+	else
+		return (y % 400) == 0
+	end
 end
 
-local function month_length ( m , y )
+local function month_length(m, y)
 	if m == 2 then
-		return is_leap ( y ) and 29 or 28
+		return is_leap(y) and 29 or 28
 	else
-		return mon_lengths [ m ]
+		return mon_lengths[m]
 	end
 end
 
-local function leap_years_since ( year )
-	return idiv ( year , 4 ) - idiv ( year , 100 ) + idiv ( year , 400 )
+local function leap_years_since(year)
+	return idiv(year, 4) - idiv(year, 100) + idiv(year, 400)
 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
 		yday = yday + 1
 	end
 	return yday + day
 end
 
-local function day_of_week ( day , month , year )
+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
+	return(year + leap_years_since(year) + sakamoto[month] + day) % 7 + 1
 end
 
-local function increment ( tens , units , base )
+local function borrow(tens, units, base)
+	local frac = tens % 1
+	units = units + frac * base
+	tens = tens - frac
+	return tens, units
+end
+
+local function carry(tens, units, base)
 	if units >= base then
-		tens  = tens + idiv ( units , base )
+		tens  = tens + idiv(units, base)
 		units = units % base
 	elseif units < 0 then
-		tens  = tens - 1 + idiv ( -units , base )
-		units = base - ( -units % base )
+		tens  = tens + idiv(units, base)
+		units = (base + units) % base
 	end
-	return tens , units
+	return tens, units
 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?
-	hour , min  = increment ( hour , min  , 60 )
-	day  , hour = increment ( day  , hour , 24 )
-
-	while day <= 0 do
-		year = year - 1
-		day  = day + year_length ( year )
+local function normalise(year, month, day, hour, min, sec)
+	-- `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
+		month = month - 1
+		if month < 0 then
+			year = year - 1
+			month = 11
+		end
+		day = day + month_length(month + 1, 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
-		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
-		if month > 12 then
-			month = 1
+		if month >= 12 then
+			month = 0
 			year = year + 1
 		end
 	end
 
-	return year , month , day , hour , min , sec
+	-- 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
 
-local leap_years_since_1970 = leap_years_since ( 1970 )
-local function timestamp ( year , month , day , hour , min , sec )
-	year , month , day , hour , min , sec = normalise ( year , month , day , hour , min , sec )
+local leap_years_since_1970 = leap_years_since(1970)
+local function timestamp(year, month, day, hour, min, sec)
+	year, month, day, hour, min, sec = normalise(year, month, day, hour, min, sec)
 
-	local days_since_epoch = day_of_year ( day , month , year )
-		+ 365 * ( year - 1970 )
+	local days_since_epoch = day_of_year(day, month, year)
+		+ 365 * (year - 1970)
 		-- Each leap year adds one day
-		+ ( leap_years_since ( year - 1 ) - leap_years_since_1970 ) - 1
+		+ (leap_years_since(year - 1) - leap_years_since_1970) - 1
 
 	return days_since_epoch * (60*60*24)
-		+ hour  * (60*60)
-		+ min   * 60
+		+ hour * (60*60)
+		+ min  * 60
 		+ sec
 end
 
 
-local timetable_methods = { }
+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 ,
+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 ( self:unpack ( ) )
+function timetable_methods:normalise()
+	local year, month, day
+	year, month, day, self.hour, self.min, self.sec = normalise(self:unpack())
 
 	self.day   = day
 	self.month = month
 	self.year  = year
-	self.yday  = day_of_year ( day , month , year )
-	self.wday  = day_of_week ( day , month , year )
+	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 ( self:unpack ( ) )
+function timetable_methods:timestamp()
+	return timestamp(self:unpack())
 end
 
-function timetable_methods:rfc_3339 ( )
-	-- %06.3f gives 3 (=6-3) digits after decimal
-	return strformat ( "%04u-%02u-%02uT%02u:%02u:%06.3f" , self:unpack ( ) )
+function timetable_methods:rfc_3339()
+	local year, month, day, hour, min, fsec = self:unpack()
+	local sec, msec = borrow(fsec, 0, 1000)
+	msec = math.floor(msec)
+	return strformat("%04u-%02u-%02uT%02u:%02u:%02d.%03d", year, month, day, hour, min, sec, msec)
 end
 
-local strftime = require "luatz.strftime".strftime
-function timetable_methods:strftime ( format_string )
-	return strftime ( format_string , self )
-end
-
-local timetable_mt = {
-	__index    = timetable_methods ;
-	__tostring = timetable_methods.rfc_3339 ;
-	__eq = function ( a , b )
-		return a:timestamp ( ) == b:timestamp ( )
-	end ;
-	__lt = function ( a , b )
-		return a:timestamp ( ) < b:timestamp ( )
-	end ;
+function timetable_methods:strftime(format_string)
+	return strftime(format_string, self)
+end
+
+local timetable_mt
+
+local function coerce_arg(t)
+	if getmetatable(t) == timetable_mt then
+		return t:timestamp()
+	end
+	return t
+end
+
+timetable_mt = {
+	__index    = timetable_methods;
+	__tostring = timetable_methods.rfc_3339;
+	__eq = function(a, b)
+		return a:timestamp() == b:timestamp()
+	end;
+	__lt = function(a, b)
+		return a:timestamp() < b:timestamp()
+	end;
+	__sub = function(a, b)
+		return coerce_arg(a) - coerce_arg(b)
+	end;
 }
 
-local function cast_timetable ( tm )
-	return setmetatable ( tm , timetable_mt )
+local function cast_timetable(tm)
+	return setmetatable(tm, timetable_mt)
 end
 
-local function new_timetable ( year , month , day , hour , min , sec , yday , wday )
+local function new_timetable(year, month, day, hour, min, sec, yday, wday)
 	return cast_timetable {
-		year  = year ;
-		month = month ;
-		day   = day ;
-		hour  = hour ;
-		min   = min ;
-		sec   = sec ;
-		yday  = yday ;
-		wday  = wday ;
+		year  = year;
+		month = month;
+		day   = day;
+		hour  = hour;
+		min   = min;
+		sec   = sec;
+		yday  = yday;
+		wday  = wday;
 	}
 end
 
-function timetable_methods:clone ( )
-	return new_timetable ( self:unpack ( ) )
+function timetable_methods:clone()
+	return new_timetable(self:unpack())
 end
 
-local function new_from_timestamp ( ts )
-	return new_timetable ( 1970 , 1 , 1 , 0 , 0 , ts )
+local function new_from_timestamp(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 {
-	day_of_year = day_of_year ;
-	day_of_week = day_of_week ;
-	normalise = normalise ;
-	timestamp = timestamp ;
-
-	new = new_timetable ;
-	new_from_timestamp = new_from_timestamp ;
-	cast = cast_timetable ;
-	timetable_mt = timetable_mt ;
+	is_leap = is_leap;
+	day_of_year = day_of_year;
+	day_of_week = day_of_week;
+	normalise = normalise;
+	timestamp = timestamp;
+
+	new = new_timetable;
+	new_from_timestamp = new_from_timestamp;
+	cast = cast_timetable;
+	timetable_mt = timetable_mt;
 }