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josevalim merged 2 commits into from
Sep 21, 2026
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Avoid repeated conversions when shifting Calendar.ISO datetimes #15924

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9c93b6a
Avoid repeated conversions when shifting Calendar.ISO datetimes
preciz Sep 21, 2026
a56c2c5
Group Calendar.ISO datetime shift tests
preciz Sep 21, 2026
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48 changes: 29 additions & 19 deletions lib/elixir/lib/calendar/iso.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -1881,23 +1881,32 @@ defmodule Calendar.ISO do
microsecond,
Duration.t()
) :: {year, month, day, hour, minute, second, microsecond}
def shift_naive_datetime(year, month, day, hour, minute, second, microsecond, duration) do
shift_options = shift_datetime_options(duration)
def shift_naive_datetime(
year,
month,
day,
hour,
minute,
second,
{value, _} = microsecond,
duration
) do
{months, seconds, shift_microsecond} = shift_datetime_units(duration)

Enum.reduce(shift_options, {year, month, day, hour, minute, second, microsecond}, fn
{:microsecond, {0, _}}, naive_datetime ->
naive_datetime
{year, month, day} =
if months == 0, do: {year, month, day}, else: shift_months({year, month, day}, months)

{_, 0}, naive_datetime ->
naive_datetime
datetime = {year, month, day, hour, minute, second, microsecond}
{microseconds, precision} = shift_time_unit_values(shift_microsecond, microsecond)

{:month, value}, {year, month, day, hour, minute, second, microsecond} ->
{new_year, new_month, new_day} = shift_months({year, month, day}, value)
{new_year, new_month, new_day, hour, minute, second, microsecond}
if seconds == 0 and microseconds == 0 do
datetime
else
total_microseconds = seconds * @microseconds_per_second + microseconds

{time_unit, value}, naive_datetime ->
shift_time_unit(naive_datetime, value, time_unit)
end)
datetime = put_elem(datetime, 6, {value, precision})
shift_time_unit(datetime, total_microseconds, :microsecond)
end
end

@doc """
Expand Down Expand Up @@ -2012,7 +2021,8 @@ defmodule Calendar.ISO do
"cannot shift date by time scale unit. Expected :year, :month, :week, :day"
end

defp shift_datetime_options(%Duration{
@compile {:inline, shift_datetime_units: 1}
defp shift_datetime_units(%Duration{
year: year,
month: month,
week: week,
Expand All @@ -2022,11 +2032,11 @@ defmodule Calendar.ISO do
second: second,
microsecond: microsecond
}) do
[
month: year * 12 + month,
second: week * 7 * 86_400 + day * 86_400 + hour * 3600 + minute * 60 + second,
microsecond: microsecond
]
{
year * 12 + month,
(((week * @days_per_week + day) * 24 + hour) * 60 + minute) * 60 + second,

@preciz preciz Sep 21, 2026

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nesting in parentheses here allows the compiler to better optimize

microsecond
}
end

defp shift_time_options(%Duration{
Expand Down
307 changes: 164 additions & 143 deletions lib/elixir/test/elixir/calendar/iso_test.exs
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Expand Up @@ -484,149 +484,170 @@ defmodule Calendar.ISOTest do
assert Calendar.ISO.shift_date(2024, 1, 31, Duration.new!(month: 9)) == {2024, 10, 31}
end

test "shift_naive_datetime/2" do
assert Calendar.ISO.shift_naive_datetime(
2024,
3,
2,
0,
0,
0,
{0, 0},
Duration.new!([])
) == {2024, 3, 2, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
1,
1,
0,
0,
0,
{0, 0},
Duration.new!(year: 1)
) == {2001, 1, 1, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
1,
1,
0,
0,
0,
{0, 0},
Duration.new!(month: 1)
) == {2000, 2, 1, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
1,
1,
0,
0,
0,
{0, 0},
Duration.new!(month: 1, day: 28)
) == {2000, 2, 29, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
1,
1,
0,
0,
0,
{0, 0},
Duration.new!(month: 1, day: 30)
) == {2000, 3, 2, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
1,
1,
0,
0,
0,
{0, 0},
Duration.new!(month: 2, day: 29)
) == {2000, 3, 30, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
2,
29,
0,
0,
0,
{0, 0},
Duration.new!(year: -1)
) == {1999, 2, 28, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
2,
29,
0,
0,
0,
{0, 0},
Duration.new!(month: -1)
) == {2000, 1, 29, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
2,
29,
0,
0,
0,
{0, 0},
Duration.new!(month: -1, day: -28)
) == {2000, 1, 1, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
2,
29,
0,
0,
0,
{0, 0},
Duration.new!(month: -1, day: -30)
) == {1999, 12, 30, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
2,
29,
0,
0,
0,
{0, 0},
Duration.new!(month: -1, day: -29)
) == {1999, 12, 31, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
1,
1,
0,
0,
0,
{0, 0},
Duration.new!(hour: 12)
) == {2000, 1, 1, 12, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
1,
1,
0,
0,
0,
{0, 0},
Duration.new!(minute: -65)
) == {1999, 12, 31, 22, 55, 0, {0, 0}}
describe "shift_naive_datetime/8" do
test "shifts by duration" do
assert Calendar.ISO.shift_naive_datetime(
2024,
3,
2,
0,
0,
0,
{0, 0},
Duration.new!([])
) == {2024, 3, 2, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
1,
1,
0,
0,
0,
{0, 0},
Duration.new!(year: 1)
) == {2001, 1, 1, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
1,
1,
0,
0,
0,
{0, 0},
Duration.new!(month: 1)
) == {2000, 2, 1, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
1,
1,
0,
0,
0,
{0, 0},
Duration.new!(month: 1, day: 28)
) == {2000, 2, 29, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
1,
1,
0,
0,
0,
{0, 0},
Duration.new!(month: 1, day: 30)
) == {2000, 3, 2, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
1,
1,
0,
0,
0,
{0, 0},
Duration.new!(month: 2, day: 29)
) == {2000, 3, 30, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
2,
29,
0,
0,
0,
{0, 0},
Duration.new!(year: -1)
) == {1999, 2, 28, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
2,
29,
0,
0,
0,
{0, 0},
Duration.new!(month: -1)
) == {2000, 1, 29, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
2,
29,
0,
0,
0,
{0, 0},
Duration.new!(month: -1, day: -28)
) == {2000, 1, 1, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
2,
29,
0,
0,
0,
{0, 0},
Duration.new!(month: -1, day: -30)
) == {1999, 12, 30, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
2,
29,
0,
0,
0,
{0, 0},
Duration.new!(month: -1, day: -29)
) == {1999, 12, 31, 0, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
1,
1,
0,
0,
0,
{0, 0},
Duration.new!(hour: 12)
) == {2000, 1, 1, 12, 0, 0, {0, 0}}

assert Calendar.ISO.shift_naive_datetime(
2000,
1,
1,
0,
0,
0,
{0, 0},
Duration.new!(minute: -65)
) == {1999, 12, 31, 22, 55, 0, {0, 0}}
end

test "preserves precision for zero microsecond shifts" do
for second <- [-1, 0, 1], precision <- [0, 6] do
duration = Duration.new!(second: second, microsecond: {0, precision})

assert Calendar.ISO.shift_naive_datetime(2024, 1, 31, 12, 0, 30, {120_000, 3}, duration) ==
{2024, 1, 31, 12, 0, 30 + second, {120_000, 3}}
end
end

test "updates precision when time shifts cancel" do
for second <- [-1, 1], precision <- [2, 6] do
duration =
Duration.new!(month: 1, second: second, microsecond: {-second * 1_000_000, precision})

assert Calendar.ISO.shift_naive_datetime(2024, 1, 31, 12, 0, 0, {120_000, 3}, duration) ==
{2024, 2, 29, 12, 0, 0, {120_000, precision}}
end
end
end
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test "shift_time/2" do
Expand Down
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