Issue #23517: fromtimestamp() and utcfromtimestamp() methods of

datetime.datetime now round microseconds to nearest with ties going to nearest
even integer (ROUND_HALF_EVEN), as round(float), instead of rounding towards
-Infinity (ROUND_FLOOR).

pytime API: replace _PyTime_ROUND_HALF_UP with _PyTime_ROUND_HALF_EVEN. Fix
also _PyTime_Divide() for negative numbers.

_PyTime_AsTimeval_impl() now reuses _PyTime_Divide() instead of reimplementing
rounding modes.

Lib/datetime.py

@@ -1380,7 +1380,7 @@ class datetime(date):
         A timezone info object may be passed in as well.
         """
         frac, t = _math.modf(t)
-        us = _round_half_up(frac * 1e6)
+        us = round(frac * 1e6)
         if us >= 1000000:
             t += 1
             us -= 1000000