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gh-122681: merge m_atan2() and c_atan2() helper functions #122682

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Merged
merged 7 commits into from
Aug 6, 2024
Merged

gh-122681: merge m_atan2() and c_atan2() helper functions #122682

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dc453f6
gh-122681: merge m_atan2() and c_atan2() helper functions
skirpichev Aug 5, 2024
5a2f3fe
Merge branch 'main' into m_atan2-122681
skirpichev Aug 5, 2024
128281b
XXX pin attrs
skirpichev Aug 5, 2024
6a11322
Revert "XXX pin attrs"
skirpichev Aug 6, 2024
128023c
revert news entry too
skirpichev Aug 6, 2024
2f06e6e
Merge branch 'master' into m_atan2-122681
skirpichev Aug 6, 2024
a4a4d46
Merge branch 'main' into m_atan2-122681
vstinner Aug 6, 2024
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39 changes: 39 additions & 0 deletions Modules/_math.h
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Original file line number Diff line number Diff line change
Expand Up @@ -23,3 +23,42 @@ _Py_log1p(double x)
}

#define m_log1p _Py_log1p

/*
wrapper for atan2 that deals directly with special cases before
delegating to the platform libm for the remaining cases. This
is necessary to get consistent behaviour across platforms.
Windows, FreeBSD and alpha Tru64 are amongst platforms that don't
always follow C99. Windows screws up atan2 for inf and nan, and
alpha Tru64 5.1 doesn't follow C99 for atan2(0., 0.).
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I'm curious if Windows and FreeBSD still need these workaround in 2024. But I don't ask you to test ;-)

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I'm curious if Windows and FreeBSD still need these workaround in 2024.

I doubt, especially FreeBSD.

As I said in the description, most functions in the cmath works with libm's atan2 function (e.g. acos). I think it's safe to remove these helpers. But this should be heavily tested. Here is a draft pr with this attempt: #122715

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I doubt, especially FreeBSD.

Right. When I added math.fma(), I found a bug on FreeBSD. It takes a while to get it fixed upstream, but it's being fixed: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=277783 :-)

*/

static double
_Py_atan2(double y, double x)
{
if (isnan(x) || isnan(y))
return Py_NAN;
if (isinf(y)) {
if (isinf(x)) {
if (copysign(1., x) == 1.)
/* atan2(+-inf, +inf) == +-pi/4 */
return copysign(0.25*Py_MATH_PI, y);
else
/* atan2(+-inf, -inf) == +-pi*3/4 */
return copysign(0.75*Py_MATH_PI, y);
}
/* atan2(+-inf, x) == +-pi/2 for finite x */
return copysign(0.5*Py_MATH_PI, y);
}
if (isinf(x) || y == 0.) {
if (copysign(1., x) == 1.)
/* atan2(+-y, +inf) = atan2(+-0, +x) = +-0. */
return copysign(0., y);
else
/* atan2(+-y, -inf) = atan2(+-0., -x) = +-pi. */
return copysign(Py_MATH_PI, y);
}
return atan2(y, x);
}

#define m_atan2 _Py_atan2
34 changes: 2 additions & 32 deletions Modules/cmathmodule.c
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Expand Up @@ -324,36 +324,6 @@ cmath_atan_impl(PyObject *module, Py_complex z)
return r;
}

/* Windows screws up atan2 for inf and nan, and alpha Tru64 5.1 doesn't follow
C99 for atan2(0., 0.). */
static double
c_atan2(Py_complex z)
{
if (isnan(z.real) || isnan(z.imag))
return Py_NAN;
if (isinf(z.imag)) {
if (isinf(z.real)) {
if (copysign(1., z.real) == 1.)
/* atan2(+-inf, +inf) == +-pi/4 */
return copysign(0.25*Py_MATH_PI, z.imag);
else
/* atan2(+-inf, -inf) == +-pi*3/4 */
return copysign(0.75*Py_MATH_PI, z.imag);
}
/* atan2(+-inf, x) == +-pi/2 for finite x */
return copysign(0.5*Py_MATH_PI, z.imag);
}
if (isinf(z.real) || z.imag == 0.) {
if (copysign(1., z.real) == 1.)
/* atan2(+-y, +inf) = atan2(+-0, +x) = +-0. */
return copysign(0., z.imag);
else
/* atan2(+-y, -inf) = atan2(+-0., -x) = +-pi. */
return copysign(Py_MATH_PI, z.imag);
}
return atan2(z.imag, z.real);
}


static Py_complex atanh_special_values[7][7];

Expand Down Expand Up @@ -966,7 +936,7 @@ cmath_phase_impl(PyObject *module, Py_complex z)
double phi;

errno = 0;
phi = c_atan2(z); /* should not cause any exception */
phi = m_atan2(z.imag, z.real); /* should not cause any exception */
if (errno != 0)
return math_error();
else
Expand All @@ -991,7 +961,7 @@ cmath_polar_impl(PyObject *module, Py_complex z)
double r, phi;

errno = 0;
phi = c_atan2(z); /* should not cause any exception */
phi = m_atan2(z.imag, z.real); /* should not cause any exception */
r = _Py_c_abs(z); /* sets errno to ERANGE on overflow */
if (errno != 0)
return math_error();
Expand Down
37 changes: 0 additions & 37 deletions Modules/mathmodule.c
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Expand Up @@ -535,43 +535,6 @@ m_lgamma(double x)
return r;
}

/*
wrapper for atan2 that deals directly with special cases before
delegating to the platform libm for the remaining cases. This
is necessary to get consistent behaviour across platforms.
Windows, FreeBSD and alpha Tru64 are amongst platforms that don't
always follow C99.
*/

static double
m_atan2(double y, double x)
{
if (isnan(x) || isnan(y))
return Py_NAN;
if (isinf(y)) {
if (isinf(x)) {
if (copysign(1., x) == 1.)
/* atan2(+-inf, +inf) == +-pi/4 */
return copysign(0.25*Py_MATH_PI, y);
else
/* atan2(+-inf, -inf) == +-pi*3/4 */
return copysign(0.75*Py_MATH_PI, y);
}
/* atan2(+-inf, x) == +-pi/2 for finite x */
return copysign(0.5*Py_MATH_PI, y);
}
if (isinf(x) || y == 0.) {
if (copysign(1., x) == 1.)
/* atan2(+-y, +inf) = atan2(+-0, +x) = +-0. */
return copysign(0., y);
else
/* atan2(+-y, -inf) = atan2(+-0., -x) = +-pi. */
return copysign(Py_MATH_PI, y);
}
return atan2(y, x);
}


/* IEEE 754-style remainder operation: x - n*y where n*y is the nearest
multiple of y to x, taking n even in the case of a tie. Assuming an IEEE 754
binary floating-point format, the result is always exact. */
Expand Down
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