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SF bug 661086: datetime.today() truncates microseconds.

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On Windows, it was very common to get microsecond values (out of
.today() and .now()) of the form 480999, i.e. with three trailing
nines.  The platform precision is .001 seconds, and fp rounding
errors account for the rest.  Under the covers, that 480999 started
life as the fractional part of a timestamp, like .4809999978.
Rounding that times 1e6 cures the irritation.

Confession:  the platform precision isn't really .001 seconds.  It's
usually worse.  What actually happens is that MS rounds a cruder value
to a multiple of .001, and that suffers its own rounding errors.

A tiny bit of refactoring added a new internal utility to round
doubles.
This commit is contained in:
Tim Peters 2003-01-02 16:32:54 +00:00
parent e55534665f
commit 5d644dd25a
1 changed files with 16 additions and 7 deletions
Download patch file Download diff file Expand all files Collapse all files

23
Modules/datetimemodule.c
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@ -120,6 +120,19 @@ divmod(int x, int y, int *r)
return quo;
}
/* Round a double to the nearest long. |x| must be small enough to fit
* in a C long; this is not checked.
*/
static long
round_to_long(double x)
{
if (x >= 0.0)
x = floor(x + 0.5);
else
x = ceil(x - 0.5);
return (long)x;
}
/* ---------------------------------------------------------------------------
* General calendrical helper functions
*/
@ -1905,12 +1918,7 @@ delta_new(PyTypeObject *type, PyObject *args, PyObject *kw)
}
if (leftover_us) {
/* Round to nearest whole # of us, and add into x. */
PyObject *temp;
if (leftover_us >= 0.0)
leftover_us = floor(leftover_us + 0.5);
else
leftover_us = ceil(leftover_us - 0.5);
temp = PyLong_FromDouble(leftover_us);
PyObject *temp = PyLong_FromLong(round_to_long(leftover_us));
if (temp == NULL) {
Py_DECREF(x);
goto Done;
@ -2858,7 +2866,8 @@ static PyObject *
datetime_from_timestamp(PyObject *cls, TM_FUNC f, double timestamp)
{
time_t timet = (time_t)timestamp;
int us = (int)((timestamp - (double)timet) * 1e6);
double fraction = timestamp - (double)timet;
int us = (int)round_to_long(fraction * 1e6);
return datetime_from_timet_and_us(cls, f, timet, us);
}