fix: preserve microsecond precision in Duration for large values

src/pendulum/duration.py

@@ -95,17 +95,24 @@ def __new__(
         )
 
         # Intuitive normalization
-        total = self.total_seconds() - (years * 365 + months * 30) * SECONDS_PER_DAY
+        # Use exact integer microseconds to avoid total_seconds() float precision loss.
+        total_microseconds = (
+            (timedelta.days.__get__(self) - (years * 365 + months * 30))
+            * SECONDS_PER_DAY
+            + timedelta.seconds.__get__(self)
+        ) * US_PER_SECOND + timedelta.microseconds.__get__(self)
+        total = total_microseconds / US_PER_SECOND
         self._total = total
 
         m = 1
-        if total < 0:
+        if total_microseconds < 0:
             m = -1
 
-        self._microseconds = round(total % m * 1e6)
-        self._seconds = abs(int(total)) % SECONDS_PER_DAY * m
+        abs_microseconds = abs(total_microseconds)
+        self._microseconds = abs_microseconds % US_PER_SECOND * m
+        self._seconds = abs_microseconds // US_PER_SECOND % SECONDS_PER_DAY * m
 
-        _days = abs(int(total)) // SECONDS_PER_DAY * m
+        _days = abs_microseconds // US_PER_SECOND // SECONDS_PER_DAY * m
         self._days = _days
         self._remaining_days = abs(_days) % 7 * m
         self._weeks = abs(_days) // 7 * m
@@ -509,11 +516,15 @@ def __new__(
         )
 
         # Intuitive normalization
-        self._total = delta.total_seconds()
-        total = abs(self._total)
-
-        self._microseconds = round(total % 1 * 1e6)
-        days, self._seconds = divmod(int(total), SECONDS_PER_DAY)
+        # Use exact integer microseconds to avoid total_seconds() float precision loss.
+        total_microseconds = (
+            delta.days * SECONDS_PER_DAY + delta.seconds
+        ) * US_PER_SECOND + delta.microseconds
+        self._total = total_microseconds / US_PER_SECOND
+        abs_microseconds = abs(total_microseconds)
+
+        self._microseconds = abs_microseconds % US_PER_SECOND
+        days, self._seconds = divmod(abs_microseconds // US_PER_SECOND, SECONDS_PER_DAY)
         self._days = abs(days + years * 365 + months * 30)
         self._weeks, self._remaining_days = divmod(days, 7)
         self._months = abs(months)

tests/duration/test_construct.py

@@ -97,3 +97,14 @@ def test_float_years_and_months():
 
     with pytest.raises(ValueError):
         pendulum.duration(months=1.5)
+
+
+def test_large_microseconds_keep_precision():
+    micro = 8999999999999999
+    pi = pendulum.duration(microseconds=micro)
+    expected = timedelta(microseconds=micro)
+    assert pi.microseconds == expected.microseconds
+    assert pi.microseconds == 999999
+
+    ai = AbsoluteDuration(microseconds=micro)
+    assert ai.microseconds == expected.microseconds == 999999