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Carry the UTC shift into the date in the Rust precise_diff #1060

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Carry the UTC shift into the date in the Rust precise_diff #1060

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113 changes: 55 additions & 58 deletions rust/src/python/helpers.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,59 @@ struct DateTimeInfo<'py> {
pub is_datetime: bool,
}

impl DateTimeInfo<'_> {
/// Subtract the UTC offset from the wall-clock fields,
/// carrying over into the day, month and year as needed.
fn shift_to_utc(&mut self) {
let seconds =
self.hour * SECS_PER_HOUR as i32 + self.minute * SECS_PER_MIN as i32 + self.second
- self.offset;
let day_shift = seconds.div_euclid(SECS_PER_DAY as i32);
let seconds = seconds.rem_euclid(SECS_PER_DAY as i32);

self.hour = seconds / SECS_PER_HOUR as i32;
self.minute = seconds % SECS_PER_HOUR as i32 / SECS_PER_MIN as i32;
self.second = seconds % SECS_PER_MIN as i32;

// UTC offsets are strictly less than a day,
// so the date moves by at most one day.
match day_shift.cmp(&0) {
Ordering::Less => {
self.day -= 1;

if self.day == 0 {
if self.month == 1 {
self.month = 12;
self.year -= 1;
} else {
self.month -= 1;
}

self.day = DAYS_PER_MONTHS[usize::from(helpers::is_leap(self.year))]
[self.month as usize];
}
}
Ordering::Greater => {
self.day += 1;

if self.day
> DAYS_PER_MONTHS[usize::from(helpers::is_leap(self.year))][self.month as usize]
{
self.day = 1;

if self.month == 12 {
self.month = 1;
self.year += 1;
} else {
self.month += 1;
}
}
}
Ordering::Equal => {}
}
}
}

impl PartialEq for DateTimeInfo<'_> {
fn eq(&self, other: &Self) -> bool {
(
Expand Down Expand Up @@ -197,35 +250,7 @@ pub fn precise_diff<'py>(
dtinfo1.microsecond = dt1dt.get_microsecond() as i32;

if !in_same_tz && dtinfo1.offset != 0 || total_days == 0 {
dtinfo1.hour -= dtinfo1.offset / SECS_PER_HOUR as i32;
dtinfo1.offset %= SECS_PER_HOUR as i32;
dtinfo1.minute -= dtinfo1.offset / SECS_PER_MIN as i32;
dtinfo1.offset %= SECS_PER_MIN as i32;
dtinfo1.second -= dtinfo1.offset;

if dtinfo1.second < 0 {
dtinfo1.second += 60;
dtinfo1.minute -= 1;
} else if dtinfo1.second > 60 {
dtinfo1.second -= 60;
dtinfo1.minute += 1;
}

if dtinfo1.minute < 0 {
dtinfo1.minute += 60;
dtinfo1.hour -= 1;
} else if dtinfo1.minute > 60 {
dtinfo1.minute -= 60;
dtinfo1.hour += 1;
}

if dtinfo1.hour < 0 {
dtinfo1.hour += 24;
dtinfo1.day -= 1;
} else if dtinfo1.hour > 24 {
dtinfo1.hour -= 24;
dtinfo1.day += 1;
}
dtinfo1.shift_to_utc();
}

dtinfo1.total_seconds = dtinfo1.hour * SECS_PER_HOUR as i32
Expand All @@ -242,35 +267,7 @@ pub fn precise_diff<'py>(
dtinfo2.microsecond = dt2dt.get_microsecond() as i32;

if !in_same_tz && dtinfo2.offset != 0 || total_days == 0 {
dtinfo2.hour -= dtinfo2.offset / SECS_PER_HOUR as i32;
dtinfo2.offset %= SECS_PER_HOUR as i32;
dtinfo2.minute -= dtinfo2.offset / SECS_PER_MIN as i32;
dtinfo2.offset %= SECS_PER_MIN as i32;
dtinfo2.second -= dtinfo2.offset;

if dtinfo2.second < 0 {
dtinfo2.second += 60;
dtinfo2.minute -= 1;
} else if dtinfo2.second > 60 {
dtinfo2.second -= 60;
dtinfo2.minute += 1;
}

if dtinfo2.minute < 0 {
dtinfo2.minute += 60;
dtinfo2.hour -= 1;
} else if dtinfo2.minute > 60 {
dtinfo2.minute -= 60;
dtinfo2.hour += 1;
}

if dtinfo2.hour < 0 {
dtinfo2.hour += 24;
dtinfo2.day -= 1;
} else if dtinfo2.hour > 24 {
dtinfo2.hour -= 24;
dtinfo2.day += 1;
}
dtinfo2.shift_to_utc();
}

dtinfo2.total_seconds = dtinfo2.hour * SECS_PER_HOUR as i32
Expand Down
27 changes: 27 additions & 0 deletions tests/test_helpers.py
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Original file line number Diff line number Diff line change
Expand Up @@ -126,6 +126,33 @@ def test_precise_diff_timezone() -> None:
assert diff.total_days == 0


def test_precise_diff_timezone_crossing_a_date_boundary() -> None:
utc = zoneinfo.ZoneInfo("UTC")
new_york = zoneinfo.ZoneInfo("America/New_York")
tokyo = zoneinfo.ZoneInfo("Asia/Tokyo")

# 2024-06-01 20:00-04:00 is 2024-06-02 00:00 UTC
dt1 = datetime(2024, 6, 1, tzinfo=utc)
dt2 = datetime(2024, 6, 1, 20, tzinfo=new_york)

assert_diff(precise_diff(dt1, dt2), days=1)
assert_diff(precise_diff(dt2, dt1), days=-1)

# 2023-12-31 20:00-05:00 is 2024-01-01 01:00 UTC
dt1 = datetime(2023, 6, 1, tzinfo=utc)
dt2 = datetime(2023, 12, 31, 20, tzinfo=new_york)

assert_diff(precise_diff(dt1, dt2), months=7, hours=1)
assert_diff(precise_diff(dt2, dt1), months=-7, hours=-1)

# 2024-03-01 05:00+09:00 is 2024-02-29 20:00 UTC
dt1 = datetime(2024, 1, 30, tzinfo=utc)
dt2 = datetime(2024, 3, 1, 5, tzinfo=tokyo)

assert_diff(precise_diff(dt1, dt2), days=30, hours=20)
assert_diff(precise_diff(dt2, dt1), days=-30, hours=-20)


def test_week_day() -> None:
assert week_day(2017, 6, 2) == 5
assert week_day(2017, 1, 1) == 7
Expand Down