File 6901-use-neri-scheider-algorithm-in-calendar.patch of Package erlang
From c87d145caa8f07d1974c17569cc070cc68e5abcc Mon Sep 17 00:00:00 2001
From: Daniel Kukula <daniel.kuku@gmail.com>
Date: Sun, 7 Dec 2025 23:51:47 +0100
Subject: [PATCH 1/4] use neri-scheider algorithm in calendar
---
lib/stdlib/src/calendar.erl | 191 +++++++++---------------------------
1 file changed, 46 insertions(+), 145 deletions(-)
diff --git a/lib/stdlib/src/calendar.erl b/lib/stdlib/src/calendar.erl
index b00df6b0da..e2521dbcf2 100644
--- a/lib/stdlib/src/calendar.erl
+++ b/lib/stdlib/src/calendar.erl
@@ -16,7 +16,7 @@
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
-%%
+%%
%% %CopyrightEnd%
%%
-module(calendar).
@@ -90,7 +90,7 @@ The following apply:
%% local and universal time, time conversions
--export([date_to_gregorian_days/1,
+-export([date_to_gregorian_days/1,
date_to_gregorian_days/3,
datetime_to_gregorian_seconds/1,
day_of_the_week/1,
@@ -104,9 +104,9 @@ The following apply:
iso_week_number/1,
last_day_of_the_month/2,
local_time/0,
- local_time_to_universal_time/1,
- local_time_to_universal_time/2,
- local_time_to_universal_time_dst/1,
+ local_time_to_universal_time/1,
+ local_time_to_universal_time/2,
+ local_time_to_universal_time_dst/1,
now_to_datetime/1, % = now_to_universal_time/1
now_to_local_time/1,
now_to_universal_time/1,
@@ -135,10 +135,16 @@ The following apply:
-define(SECONDS_PER_DAY, 86400).
-define(DAYS_PER_YEAR, 365).
-define(DAYS_PER_LEAP_YEAR, 366).
-%% -define(DAYS_PER_4YEARS, 1461).
-%% -define(DAYS_PER_100YEARS, 36524).
-%% -define(DAYS_PER_400YEARS, 146097).
-define(DAYS_FROM_0_TO_1970, 719528).
+
+%% Neri-Schneider algorithm constants.
+-define(MARCH_1_YEAR_0, 60). % Gregorian days from Jan 1 year 0 to Mar 1 year 0
+-define(DAYS_PER_ERA, 146097). % Days in 400 years
+-define(DAYS_PER_4_YEARS, 1460). % 365 * 4 (without leap adjustment)
+-define(DAYS_PER_100_YEARS, 36524). % Days in 100 years
+-define(YEARS_PER_ERA, 400).
+-define(DAYS_PER_5_MONTHS, 153). % Days in Mar-Apr-May-Jun-Jul
+-define(MONTHS_PER_CYCLE, 5).
-define(DAYS_FROM_0_TO_10000, 2932897).
-define(SECONDS_FROM_0_TO_1970, (?DAYS_FROM_0_TO_1970*?SECONDS_PER_DAY)).
-define(SECONDS_FROM_0_TO_10000, (?DAYS_FROM_0_TO_10000*?SECONDS_PER_DAY)).
@@ -225,11 +231,15 @@ The time unit used by the rfc3339 conversion functions.
Day :: day(),
Days :: non_neg_integer().
date_to_gregorian_days(Year, Month, Day) when is_integer(Day), Day > 0 ->
- Last = last_day_of_the_month(Year, Month),
- if
- Day =< Last ->
- dy(Year) + dm(Month) + df(Year, Month) + Day - 1
- end.
+ %% Neri-Schneider algorithm.
+ %% Shift year so March is first month (simplifies leap year handling).
+ Y = if Month =< 2 -> Year - 1; true -> Year end,
+ Era = if Y >= 0 -> Y div ?YEARS_PER_ERA; true -> (Y - 399) div ?YEARS_PER_ERA end,
+ YearOfEra = Y - Era * ?YEARS_PER_ERA,
+ MonthPrime = if Month > 2 -> Month - 3; true -> Month + 9 end,
+ DayOfYear = ?DAYS_PER_5_MONTHS * MonthPrime div ?MONTHS_PER_CYCLE + Day - 1,
+ DayOfEra = ?DAYS_PER_YEAR * YearOfEra + YearOfEra div 4 - YearOfEra div 100 + DayOfYear,
+ Era * ?DAYS_PER_ERA + DayOfEra + ?MARCH_1_YEAR_0.
-spec date_to_gregorian_days(Date) -> Days when
Date :: date(),
@@ -288,9 +298,20 @@ day_of_the_week({Year, Month, Day}) ->
-spec gregorian_days_to_date(Days) -> date() when
Days :: non_neg_integer().
gregorian_days_to_date(Days) ->
- {Year, DayOfYear} = day_to_year(Days),
- {Month, DayOfMonth} = year_day_to_date(Year, DayOfYear),
- {Year, Month, DayOfMonth}.
+ %% Neri-Schneider algorithm.
+ %% Shift to March 1, year 0 epoch.
+ Z = Days - ?MARCH_1_YEAR_0,
+ Era = if Z >= 0 -> Z div ?DAYS_PER_ERA; true -> (Z - ?DAYS_PER_ERA + 1) div ?DAYS_PER_ERA end,
+ DayOfEra = Z - Era * ?DAYS_PER_ERA,
+ YearOfEra = (DayOfEra - DayOfEra div ?DAYS_PER_4_YEARS + DayOfEra div ?DAYS_PER_100_YEARS
+ - DayOfEra div (?DAYS_PER_ERA - 1)) div ?DAYS_PER_YEAR,
+ DayOfYear = DayOfEra - (?DAYS_PER_YEAR * YearOfEra + YearOfEra div 4 - YearOfEra div 100),
+ MonthPrime = (?MONTHS_PER_CYCLE * DayOfYear + 2) div ?DAYS_PER_5_MONTHS,
+ Day = DayOfYear - ?DAYS_PER_5_MONTHS * MonthPrime div ?MONTHS_PER_CYCLE + 1,
+ Month = if MonthPrime < 10 -> MonthPrime + 3; true -> MonthPrime - 9 end,
+ Y = YearOfEra + Era * ?YEARS_PER_ERA,
+ Year = if Month =< 2 -> Y + 1; true -> Y end,
+ {Year, Month, Day}.
%% gregorian_seconds_to_datetime(Secs)
@@ -498,9 +519,9 @@ local_time_to_universal_time_dst(DateTime) ->
%% Convert from erlang:timestamp() to UTC.
%%
%% Args: Now = now(); now() = {MegaSec, Sec, MilliSec}, MegaSec = Sec
-%% = MilliSec = integer()
+%% = MilliSec = integer()
%% Returns: {date(), time()}, date() = {Y, M, D}, time() = {H, M, S}.
-%%
+%%
-spec now_to_datetime(Now) -> datetime1970() when
Now :: erlang:timestamp().
now_to_datetime({MSec, Sec, _uSec}) ->
@@ -624,7 +645,7 @@ Converts a specified number of seconds into days, hours, minutes, and seconds.
seconds_to_daystime(Secs) ->
Days0 = Secs div ?SECONDS_PER_DAY,
Secs0 = Secs rem ?SECONDS_PER_DAY,
- if
+ if
Secs0 < 0 ->
{Days0 - 1, seconds_to_time(Secs0 + ?SECONDS_PER_DAY)};
true ->
@@ -783,7 +804,7 @@ system_time_to_rfc3339_do(Time, Options, Unit, OffsetOption) ->
%%
%% Returns the difference between two {Date, Time} structures.
%%
-%% T1 = T2 = {Date, Time}, Tdiff = {Day, {Hour, Min, Sec}},
+%% T1 = T2 = {Date, Time}, Tdiff = {Day, {Hour, Min, Sec}},
%% Date = {Year, Month, Day}, Time = {Hour, Minute, Sec},
%% Year = Month = Day = Hour = Minute = Sec = integer()
%%
@@ -801,7 +822,7 @@ epoch later than `T1`.
T2 :: datetime(),
Days :: integer(),
Time :: time().
-time_difference({{Y1, Mo1, D1}, {H1, Mi1, S1}},
+time_difference({{Y1, Mo1, D1}, {H1, Mi1, S1}},
{{Y2, Mo2, D2}, {H2, Mi2, S2}}) ->
Secs = datetime_to_gregorian_seconds({{Y2, Mo2, D2}, {H2, Mi2, S2}}) -
datetime_to_gregorian_seconds({{Y1, Mo1, D1}, {H1, Mi1, S1}}),
@@ -817,7 +838,7 @@ time_difference({{Y1, Mo1, D1}, {H1, Mi1, S1}},
time_to_seconds({H, M, S}) when is_integer(H), is_integer(M), is_integer(S) ->
H * ?SECONDS_PER_HOUR +
M * ?SECONDS_PER_MINUTE + S.
-
+
%% universal_time()
%%
@@ -886,45 +907,6 @@ valid_date({Y, M, D}) ->
%%
%% LOCAL FUNCTIONS
%%
--type day_of_year() :: 0..365.
-
-%% day_to_year(DayOfEpoch) = {Year, DayOfYear}
-%%
-%% The idea here is to first set the upper and lower bounds for a year,
-%% and then adjust a range by interpolation search. Although complexity
-%% of the algorithm is log(log(n)), at most 1 or 2 recursive steps
-%% are taken.
-%%
--spec day_to_year(non_neg_integer()) -> {year(), day_of_year()}.
-day_to_year(DayOfEpoch) when DayOfEpoch >= 0 ->
- YMax = DayOfEpoch div ?DAYS_PER_YEAR,
- YMin = DayOfEpoch div ?DAYS_PER_LEAP_YEAR,
- {Y1, D1} = dty(YMin, YMax, DayOfEpoch, dy(YMin), dy(YMax)),
- {Y1, DayOfEpoch - D1}.
-
--spec dty(year(), year(), non_neg_integer(), non_neg_integer(),
- non_neg_integer()) ->
- {year(), non_neg_integer()}.
-dty(Min, Max, _D1, DMin, _DMax) when Min == Max ->
- {Min, DMin};
-dty(Min, Max, D1, DMin, DMax) ->
- Diff = Max - Min,
- Mid = Min + (Diff * (D1 - DMin)) div (DMax - DMin),
- MidLength =
- case is_leap_year(Mid) of
- true -> ?DAYS_PER_LEAP_YEAR;
- false -> ?DAYS_PER_YEAR
- end,
- case dy(Mid) of
- D2 when D1 < D2 ->
- NewMax = Mid - 1,
- dty(Min, NewMax, D1, DMin, dy(NewMax));
- D2 when D1 - D2 >= MidLength ->
- NewMin = Mid + 1,
- dty(NewMin, Max, D1, dy(NewMin), DMax);
- D2 ->
- {Mid, D2}
- end.
%%
%% The Gregorian days of the iso week 01 day 1 for a given year.
@@ -939,87 +921,6 @@ gregorian_days_of_iso_w01_1(Year) ->
D0101 + 7 - DOW + 1
end.
-%% year_day_to_date(Year, DayOfYear) = {Month, DayOfMonth}
-%%
-%% Note: 1 is the first day of the month.
-%%
--spec year_day_to_date(year(), day_of_year()) -> {month(), day()}.
-year_day_to_date(Year, DayOfYear) ->
- ExtraDay = case is_leap_year(Year) of
- true ->
- 1;
- false ->
- 0
- end,
- {Month, Day} = year_day_to_date2(ExtraDay, DayOfYear),
- {Month, Day + 1}.
-
-
-%% Note: 0 is the first day of the month
-%%
--spec year_day_to_date2(0 | 1, day_of_year()) -> {month(), 0..30}.
-year_day_to_date2(_, Day) when Day < 31 ->
- {1, Day};
-year_day_to_date2(E, Day) when 31 =< Day, Day < 59 + E ->
- {2, Day - 31};
-year_day_to_date2(E, Day) when 59 + E =< Day, Day < 90 + E ->
- {3, Day - (59 + E)};
-year_day_to_date2(E, Day) when 90 + E =< Day, Day < 120 + E ->
- {4, Day - (90 + E)};
-year_day_to_date2(E, Day) when 120 + E =< Day, Day < 151 + E ->
- {5, Day - (120 + E)};
-year_day_to_date2(E, Day) when 151 + E =< Day, Day < 181 + E ->
- {6, Day - (151 + E)};
-year_day_to_date2(E, Day) when 181 + E =< Day, Day < 212 + E ->
- {7, Day - (181 + E)};
-year_day_to_date2(E, Day) when 212 + E =< Day, Day < 243 + E ->
- {8, Day - (212 + E)};
-year_day_to_date2(E, Day) when 243 + E =< Day, Day < 273 + E ->
- {9, Day - (243 + E)};
-year_day_to_date2(E, Day) when 273 + E =< Day, Day < 304 + E ->
- {10, Day - (273 + E)};
-year_day_to_date2(E, Day) when 304 + E =< Day, Day < 334 + E ->
- {11, Day - (304 + E)};
-year_day_to_date2(E, Day) when 334 + E =< Day ->
- {12, Day - (334 + E)}.
-
-%% dy(Year)
-%%
-%% Days in previous years.
-%%
--spec dy(integer()) -> non_neg_integer().
-dy(Y) when Y =< 0 ->
- 0;
-dy(Y) ->
- X = Y - 1,
- (X div 4) - (X div 100) + (X div 400) +
- X*?DAYS_PER_YEAR + ?DAYS_PER_LEAP_YEAR.
-
-%% dm(Month)
-%%
-%% Returns the total number of days in all months
-%% preceeding Month, for an ordinary year.
-%%
--spec dm(month()) ->
- 0 | 31 | 59 | 90 | 120 | 151 | 181 | 212 | 243 | 273 | 304 | 334.
-dm(1) -> 0; dm(2) -> 31; dm(3) -> 59; dm(4) -> 90;
-dm(5) -> 120; dm(6) -> 151; dm(7) -> 181; dm(8) -> 212;
-dm(9) -> 243; dm(10) -> 273; dm(11) -> 304; dm(12) -> 334.
-
-%% df(Year, Month)
-%%
-%% Accounts for an extra day in February if Year is
-%% a leap year, and if Month > 2.
-%%
--spec df(year(), month()) -> 0 | 1.
-df(_, Month) when Month < 3 ->
- 0;
-df(Year, _) ->
- case is_leap_year(Year) of
- true -> 1;
- false -> 0
- end.
-
check(_Arg, _Options, Secs) when Secs >= - ?SECONDS_FROM_0_TO_1970,
Secs < ?SECONDS_FROM_0_TO_10000 ->
ok;
--
2.51.0
