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gh-119372: Recover inf's and zeros in _Py_c_quot (GH-119457)

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In some cases, previously computed as (nan+nanj), we could
recover meaningful component values in the result, see
e.g. the C11, Annex G.5.2, routine _Cdivd().
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Sergey B Kirpichev 2024-06-29 11:00:48 +03:00 • committed by GitHub
parent 0a1e8ff9c1
commit 2cb84b107a
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3 changed files with 56 additions and 2 deletions
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25
Objects/complexobject.c
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@ -88,8 +88,7 @@ _Py_c_quot(Py_complex a, Py_complex b)
* numerators and denominator by whichever of {b.real, b.imag} has
* larger magnitude. The earliest reference I found was to CACM
* Algorithm 116 (Complex Division, Robert L. Smith, Stanford
* University). As usual, though, we're still ignoring all IEEE
* endcases.
* University).
*/
Py_complex r; /* the result */
const double abs_breal = b.real < 0 ? -b.real : b.real;
@ -120,6 +119,28 @@ _Py_c_quot(Py_complex a, Py_complex b)
/* At least one of b.real or b.imag is a NaN */
r.real = r.imag = Py_NAN;
}
/* Recover infinities and zeros that computed as nan+nanj. See e.g.
the C11, Annex G.5.2, routine _Cdivd(). */
if (isnan(r.real) && isnan(r.imag)) {
if ((isinf(a.real) || isinf(a.imag))
&& isfinite(b.real) && isfinite(b.imag))
{
const double x = copysign(isinf(a.real) ? 1.0 : 0.0, a.real);
const double y = copysign(isinf(a.imag) ? 1.0 : 0.0, a.imag);
r.real = Py_INFINITY * (x*b.real + y*b.imag);
r.imag = Py_INFINITY * (y*b.real - x*b.imag);
}
else if ((isinf(abs_breal) || isinf(abs_bimag))
&& isfinite(a.real) && isfinite(a.imag))
{
const double x = copysign(isinf(b.real) ? 1.0 : 0.0, b.real);
const double y = copysign(isinf(b.imag) ? 1.0 : 0.0, b.imag);
r.real = 0.0 * (a.real*x + a.imag*y);
r.imag = 0.0 * (a.imag*x - a.real*y);
}
}
return r;
}
#ifdef _M_ARM64