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

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().
This commit is contained in:
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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@ -94,6 +94,10 @@ class ComplexTest(unittest.TestCase):
msg += ': zeros have different signs'
self.fail(msg.format(x, y))
def assertComplexesAreIdentical(self, x, y):
self.assertFloatsAreIdentical(x.real, y.real)
self.assertFloatsAreIdentical(x.imag, y.imag)
def assertClose(self, x, y, eps=1e-9):
"""Return true iff complexes x and y "are close"."""
self.assertCloseAbs(x.real, y.real, eps)
@ -139,6 +143,33 @@ class ComplexTest(unittest.TestCase):
self.assertTrue(isnan(z.real))
self.assertTrue(isnan(z.imag))
self.assertComplexesAreIdentical(complex(INF, 1)/(0.0+1j),
complex(NAN, -INF))
# test recover of infs if numerator has infs and denominator is finite
self.assertComplexesAreIdentical(complex(INF, -INF)/(1+0j),
complex(INF, -INF))
self.assertComplexesAreIdentical(complex(INF, INF)/(0.0+1j),
complex(INF, -INF))
self.assertComplexesAreIdentical(complex(NAN, INF)/complex(2**1000, 2**-1000),
complex(INF, INF))
self.assertComplexesAreIdentical(complex(INF, NAN)/complex(2**1000, 2**-1000),
complex(INF, -INF))
# test recover of zeros if denominator is infinite
self.assertComplexesAreIdentical((1+1j)/complex(INF, INF), (0.0+0j))
self.assertComplexesAreIdentical((1+1j)/complex(INF, -INF), (0.0+0j))
self.assertComplexesAreIdentical((1+1j)/complex(-INF, INF),
complex(0.0, -0.0))
self.assertComplexesAreIdentical((1+1j)/complex(-INF, -INF),
complex(-0.0, 0))
self.assertComplexesAreIdentical((INF+1j)/complex(INF, INF),
complex(NAN, NAN))
self.assertComplexesAreIdentical(complex(1, INF)/complex(INF, INF),
complex(NAN, NAN))
self.assertComplexesAreIdentical(complex(INF, 1)/complex(1, INF),
complex(NAN, NAN))
def test_truediv_zero_division(self):
for a, b in ZERO_DIVISION:
with self.assertRaises(ZeroDivisionError):

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@ -0,0 +1,2 @@
Correct invalid corner cases in complex division (resulted in ``(nan+nanj)``
output), e.g. ``1/complex('(inf+infj)')``. Patch by Sergey B Kirpichev.

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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