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bpo-39434: Improve float __floordiv__ performance and error message #18147

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Merged
merged 1 commit into from
Jan 30, 2020
Merged

bpo-39434: Improve float __floordiv__ performance and error message #18147

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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2020-01-24-01-07-04.bpo-39434.S5ehj9.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
:term:`floor division` of float operation now has a better performance. Also
the message of :exc:`ZeroDivisionError` for this operation is updated.
Patch by Dong-hee Na.
70 changes: 39 additions & 31 deletions Objects/floatobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -611,64 +611,72 @@ float_rem(PyObject *v, PyObject *w)
return PyFloat_FromDouble(mod);
}

static PyObject *
float_divmod(PyObject *v, PyObject *w)
static void
_float_div_mod(double vx, double wx, double *floordiv, double *mod)
{
double vx, wx;
double div, mod, floordiv;
CONVERT_TO_DOUBLE(v, vx);
CONVERT_TO_DOUBLE(w, wx);
if (wx == 0.0) {
PyErr_SetString(PyExc_ZeroDivisionError, "float divmod()");
return NULL;
}
mod = fmod(vx, wx);
double div;
*mod = fmod(vx, wx);
/* fmod is typically exact, so vx-mod is *mathematically* an
exact multiple of wx. But this is fp arithmetic, and fp
vx - mod is an approximation; the result is that div may
not be an exact integral value after the division, although
it will always be very close to one.
*/
div = (vx - mod) / wx;
if (mod) {
div = (vx - *mod) / wx;
if (*mod) {
/* ensure the remainder has the same sign as the denominator */
if ((wx < 0) != (mod < 0)) {
mod += wx;
if ((wx < 0) != (*mod < 0)) {
*mod += wx;
div -= 1.0;
}
}
else {
/* the remainder is zero, and in the presence of signed zeroes
fmod returns different results across platforms; ensure
it has the same sign as the denominator. */
mod = copysign(0.0, wx);
*mod = copysign(0.0, wx);
}
/* snap quotient to nearest integral value */
if (div) {
floordiv = floor(div);
if (div - floordiv > 0.5)
floordiv += 1.0;
*floordiv = floor(div);
if (div - *floordiv > 0.5) {
*floordiv += 1.0;
}
}
else {
/* div is zero - get the same sign as the true quotient */
floordiv = copysign(0.0, vx / wx); /* zero w/ sign of vx/wx */
*floordiv = copysign(0.0, vx / wx); /* zero w/ sign of vx/wx */
}
return Py_BuildValue("(dd)", floordiv, mod);
}

static PyObject *
float_divmod(PyObject *v, PyObject *w)
{
double vx, wx;
double mod, floordiv;
CONVERT_TO_DOUBLE(v, vx);
CONVERT_TO_DOUBLE(w, wx);
if (wx == 0.0) {
PyErr_SetString(PyExc_ZeroDivisionError, "float divmod()");
return NULL;
}
_float_div_mod(vx, wx, &floordiv, &mod);
return Py_BuildValue("(dd)", floordiv, mod);
}

static PyObject *
float_floor_div(PyObject *v, PyObject *w)
{
PyObject *t, *r;

t = float_divmod(v, w);
if (t == NULL || t == Py_NotImplemented)
return t;
assert(PyTuple_CheckExact(t));
r = PyTuple_GET_ITEM(t, 0);
Py_INCREF(r);
Py_DECREF(t);
return r;
double vx, wx;
double mod, floordiv;
CONVERT_TO_DOUBLE(v, vx);
CONVERT_TO_DOUBLE(w, wx);
if (wx == 0.0) {
PyErr_SetString(PyExc_ZeroDivisionError, "float floor division by zero");
return NULL;
}
_float_div_mod(vx, wx, &floordiv, &mod);
return PyFloat_FromDouble(floordiv);
}

/* determine whether x is an odd integer or not; assumes that
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