diff options
Diffstat (limited to 'lib/stdlib/src')
-rw-r--r-- | lib/stdlib/src/calendar.erl | 39 |
1 files changed, 28 insertions, 11 deletions
diff --git a/lib/stdlib/src/calendar.erl b/lib/stdlib/src/calendar.erl index bb5d450cd6..3a083d9fda 100644 --- a/lib/stdlib/src/calendar.erl +++ b/lib/stdlib/src/calendar.erl @@ -529,24 +529,41 @@ valid_date({Y, M, D}) -> %% day_to_year(DayOfEpoch) = {Year, DayOfYear} %% -%% The idea here is to first guess a year, and then adjust. Although -%% the implementation is recursive, at most 1 or 2 recursive steps +%% 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. -%% If DayOfEpoch is very large, we need far more than 1 or 2 iterations, -%% since we just subtract a yearful of days at a time until we're there. %% -spec day_to_year(non_neg_integer()) -> {year(), day_of_year()}. day_to_year(DayOfEpoch) when DayOfEpoch >= 0 -> - Y0 = DayOfEpoch div ?DAYS_PER_YEAR, - {Y1, D1} = dty(Y0, DayOfEpoch, dy(Y0)), + 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(), non_neg_integer(), non_neg_integer()) -> +-spec dty(year(), year(), non_neg_integer(), non_neg_integer(), + non_neg_integer()) -> {year(), non_neg_integer()}. -dty(Y, D1, D2) when D1 < D2 -> - dty(Y-1, D1, dy(Y-1)); -dty(Y, _D1, D2) -> - {Y, D2}. +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. |