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Fixes #8860: Round half-microseconds to even in the timedelta constructor.

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(Original patch by Mark Dickinson.)
This commit is contained in:
Alexander Belopolsky 2013-08-04 14:51:35 -04:00
parent 5e5a8230c2
commit 790d269d39
4 changed files with 42 additions and 22 deletions
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49
Modules/_datetimemodule.c
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@ -140,19 +140,6 @@ 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;
}
/* Nearest integer to m / n for integers m and n. Half-integer results
* are rounded to even.
*/
@ -1397,7 +1384,7 @@ cmperror(PyObject *a, PyObject *b)
*/
/* Conversion factors. */
static PyObject *us_per_us = NULL; /* 1 */
static PyObject *one = NULL; /* 1 */
static PyObject *us_per_ms = NULL; /* 1000 */
static PyObject *us_per_second = NULL; /* 1000000 */
static PyObject *us_per_minute = NULL; /* 1e6 * 60 as Python int */
@ -2119,7 +2106,7 @@ delta_new(PyTypeObject *type, PyObject *args, PyObject *kw)
goto Done
if (us) {
y = accum("microseconds", x, us, us_per_us, &leftover_us);
y = accum("microseconds", x, us, one, &leftover_us);
CLEANUP;
}
if (ms) {
@ -2148,7 +2135,33 @@ delta_new(PyTypeObject *type, PyObject *args, PyObject *kw)
}
if (leftover_us) {
/* Round to nearest whole # of us, and add into x. */
PyObject *temp = PyLong_FromLong(round_to_long(leftover_us));
double whole_us = round(leftover_us);
int x_is_odd;
PyObject *temp;
whole_us = round(leftover_us);
if (fabs(whole_us - leftover_us) == 0.5) {
/* We're exactly halfway between two integers. In order
* to do round-half-to-even, we must determine whether x
* is odd. Note that x is odd when it's last bit is 1. The
* code below uses bitwise and operation to check the last
* bit. */
temp = PyNumber_And(x, one); /* temp <- x & 1 */
if (temp == NULL) {
Py_DECREF(x);
goto Done;
}
x_is_odd = PyObject_IsTrue(temp);
Py_DECREF(temp);
if (x_is_odd == -1) {
Py_DECREF(x);
goto Done;
}
whole_us = 2.0 * round((leftover_us + x_is_odd) * 0.5) - x_is_odd;
}
temp = PyLong_FromLong(whole_us);
if (temp == NULL) {
Py_DECREF(x);
goto Done;
@ -5351,12 +5364,12 @@ PyInit__datetime(void)
assert(DI100Y == 25 * DI4Y - 1);
assert(DI100Y == days_before_year(100+1));
us_per_us = PyLong_FromLong(1);
one = PyLong_FromLong(1);
us_per_ms = PyLong_FromLong(1000);
us_per_second = PyLong_FromLong(1000000);
us_per_minute = PyLong_FromLong(60000000);
seconds_per_day = PyLong_FromLong(24 * 3600);
if (us_per_us == NULL || us_per_ms == NULL || us_per_second == NULL ||
if (one == NULL || us_per_ms == NULL || us_per_second == NULL ||
us_per_minute == NULL || seconds_per_day == NULL)
return NULL;