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fix: DateTime.add/3 :nanosecond precision error #34

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fix: DateTime.add/3 :nanosecond precision error #34

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0d91b9e
introduce test that reproduces the issue
ceolinrenato Jun 27, 2025
156be7b
support nanosecs on iso_days_to_gregorian_seconds/1
ceolinrenato Jun 27, 2025
7f2fbb3
generalize conversion
ceolinrenato Jun 27, 2025
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5 changes: 3 additions & 2 deletions lib/tz/time_zone_database.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -132,8 +132,9 @@ defmodule Tz.TimeZoneDatabase do
|> Tz.PeriodsBuilder.periods_to_tuples_and_reverse()
end

defp iso_days_to_gregorian_seconds({days, {parts_in_day, 86_400_000_000}}) do
div(days * 86_400_000_000 + parts_in_day, 1_000_000)
defp iso_days_to_gregorian_seconds({days, {parts_in_day, unit_in_day}}) do
units_per_second = div(unit_in_day, 86_400)
div(days * unit_in_day + parts_in_day, units_per_second)
end

defp naive_datetime_to_gregorian_seconds(%{calendar: Calendar.ISO, year: year}) when year < 0,
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7 changes: 7 additions & 0 deletions test/time_zone_database_test.exs
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Expand Up @@ -171,6 +171,13 @@ defmodule TimeZoneDatabaseTest do
assert DateTime.to_iso8601(datetime) == "2030-01-01T00:00:00+00:00"
end

test "supports nanoseconds precision" do
date_time_utc = ~U[2029-12-31 10:15:00.000000Z]

assert ~U[2029-12-31 10:15:00.000001Z] ==
DateTime.add(date_time_utc, 1_000, :nanosecond, Tz.TimeZoneDatabase)
end

test "next_period/1" do
{:ok, dt} =
DateTime.new(~D[2030-09-01], ~T[10:00:00], "Europe/Copenhagen", Tz.TimeZoneDatabase)
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