STINNER Victor <[email protected]> added the comment:
Oh, clang on FreeBSD spotted a similar bug in float.__trunc__()!
static PyObject *
float___trunc___impl(PyObject *self)
/*[clinic end generated code: output=dd3e289dd4c6b538 input=591b9ba0d650fdff]*/
{
double x = PyFloat_AsDouble(self);
double wholepart; /* integral portion of x, rounded toward 0 */
(void)modf(x, &wholepart);
/* Try to get out cheap if this fits in a Python int. The attempt
* to cast to long must be protected, as C doesn't define what
* happens if the double is too big to fit in a long. Some rare
* systems raise an exception then (RISCOS was mentioned as one,
* and someone using a non-default option on Sun also bumped into
* that). Note that checking for >= and <= LONG_{MIN,MAX} would
* still be vulnerable: if a long has more bits of precision than
* a double, casting MIN/MAX to double may yield an approximation,
* and if that's rounded up, then, e.g., wholepart=LONG_MAX+1 would
* yield true from the C expression wholepart<=LONG_MAX, despite
* that wholepart is actually greater than LONG_MAX.
*/
if (LONG_MIN < wholepart && wholepart < LONG_MAX) { /* <=== HERE */
const long aslong = (long)wholepart;
return PyLong_FromLong(aslong);
}
return PyLong_FromDouble(wholepart);
}
Objects/floatobject.c:881:45: warning: implicit conversion from 'long' to
'double' changes value from 9223372036854775807 to 9223372036854775808
[-Wimplicit-int-float-conversion]
if (LONG_MIN < wholepart && wholepart < LONG_MAX) {
~ ^~~~~~~~
/usr/include/sys/limits.h:64:18: note: expanded from macro 'LONG_MAX'
#define LONG_MAX __LONG_MAX /* max for a long */
^~~~~~~~~~
/usr/include/x86/_limits.h:64:20: note: expanded from macro '__LONG_MAX'
#define __LONG_MAX 0x7fffffffffffffff /* max for a long */
^~~~~~~~~~~~~~~~~~
1 warning generated.
----------
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Python tracker <[email protected]>
<https://bugs.python.org/issue39277>
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