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SF bug 115831 and Ping's SF patch 101751, 0.0**-2.0 returns inf rather than

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raise ValueError.  Checked in the patch as far as it went, but also changed
all of ints, longs and floats to raise ZeroDivisionError instead when raising
0 to a negative number.  This is what 754-inspired stds require, as the "true
result" is an infinity obtained from finite operands, i.e. it's a singularity.
Also changed float pow to not be so timid about using its square-and-multiply
algorithm.  Note that what math.pow does is unrelated to what builtin pow
does, and will still vary by platform.
This commit is contained in:
Tim Peters 2000-10-06 00:36:09 +00:00
parent 4779a0a6fd
commit c54d19043a
4 changed files with 102 additions and 62 deletions
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63
Objects/floatobject.c
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@ -449,20 +449,33 @@ float_pow(PyFloatObject *v, PyObject *w, PyFloatObject *z)
iv = v->ob_fval;
iw = ((PyFloatObject *)w)->ob_fval;
intw = (long)iw;
if (iw == intw && -10000 < intw && intw < 10000) {
/* Sort out special cases here instead of relying on pow() */
if (intw == 0) { /* x**0 is 1, even 0**0 */
PyFPE_START_PROTECT("pow", return 0)
if ((PyObject *)z!=Py_None) {
ix=fmod(1.0, z->ob_fval);
if (ix!=0 && z->ob_fval<0) ix+=z->ob_fval;
}
else ix=1.0;
PyFPE_END_PROTECT(ix)
return PyFloat_FromDouble(ix);
/* Sort out special cases here instead of relying on pow() */
if (iw == 0) { /* x**0 is 1, even 0**0 */
PyFPE_START_PROTECT("pow", return NULL)
if ((PyObject *)z != Py_None) {
ix = fmod(1.0, z->ob_fval);
if (ix != 0 && z->ob_fval < 0)
ix += z->ob_fval;
}
else
ix = 1.0;
PyFPE_END_PROTECT(ix)
return PyFloat_FromDouble(ix);
}
if (iv == 0.0) {
if (iw < 0.0) {
PyErr_SetString(PyExc_ZeroDivisionError,
"0.0 to a negative power");
return NULL;
}
return PyFloat_FromDouble(0.0);
}
if (iw == intw && intw > LONG_MIN) {
/* ruled out LONG_MIN because -LONG_MIN isn't representable */
errno = 0;
PyFPE_START_PROTECT("pow", return 0)
PyFPE_START_PROTECT("pow", return NULL)
if (intw > 0)
ix = powu(iv, intw);
else
@ -471,21 +484,13 @@ float_pow(PyFloatObject *v, PyObject *w, PyFloatObject *z)
}
else {
/* Sort out special cases here instead of relying on pow() */
if (iv == 0.0) {
if (iw < 0.0) {
PyErr_SetString(PyExc_ValueError,
"0.0 to a negative power");
return NULL;
}
return PyFloat_FromDouble(0.0);
}
if (iv < 0.0) {
PyErr_SetString(PyExc_ValueError,
"negative number to a float power");
return NULL;
}
errno = 0;
PyFPE_START_PROTECT("pow", return 0)
PyFPE_START_PROTECT("pow", return NULL)
ix = pow(iv, iw);
PyFPE_END_PROTECT(ix)
}
@ -495,13 +500,15 @@ float_pow(PyFloatObject *v, PyObject *w, PyFloatObject *z)
PyErr_SetFromErrno(PyExc_OverflowError);
return NULL;
}
if ((PyObject *)z!=Py_None) {
PyFPE_START_PROTECT("pow", return 0)
ix=fmod(ix, z->ob_fval); /* XXX To Be Rewritten */
if ( ix!=0 &&
((iv<0 && z->ob_fval>0) || (iv>0 && z->ob_fval<0) )) {
ix+=z->ob_fval;
}
if ((PyObject *)z != Py_None) {
PyFPE_START_PROTECT("pow", return NULL)
ix = fmod(ix, z->ob_fval); /* XXX To Be Rewritten */
if (ix != 0 &&
((iv < 0 && z->ob_fval > 0) ||
(iv > 0 && z->ob_fval < 0)
)) {
ix += z->ob_fval;
}
PyFPE_END_PROTECT(ix)
}
return PyFloat_FromDouble(ix);