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Merge m_atan2() and c_atan2() helper functions (or replace libm's atan2) #122681

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skirpichev opened this issue Aug 5, 2024 · 0 comments
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Merge m_atan2() and c_atan2() helper functions (or replace libm's atan2) #122681

skirpichev opened this issue Aug 5, 2024 · 0 comments
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type-feature A feature request or enhancement

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@skirpichev
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skirpichev commented Aug 5, 2024 •
edited by bedevere-app bot
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Feature or enhancement

Proposal:

With #29179, many workarounds for buggy libm implementations were removed. Yet, there is m_atan2():

cpython/Modules/mathmodule.c

Lines 546 to 572 in d0b92dd

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);
}

and

cpython/Modules/cmathmodule.c

Lines 329 to 355 in d0b92dd

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);
}

They are identical, the second one just uses Py_complex to keep arguments.

We should either 1) move first helper to _math.h and reuse it in the cmathmodule.c or 2) just remove these helpers. I'll provide patch for 1) proposal.

But 2) looks also safe for me: it seems that c_atan2() helper was used only for cmath.phase() and cmath.polar(); libm's atan2() used for the rest - and this don't poses any problems in CI or build bots. ("Problem" values are tested, e.g. infinities and nans for acos().)

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs
@skirpichev skirpichev added the type-feature A feature request or enhancement label Aug 5, 2024
skirpichev added a commit to skirpichev/cpython that referenced this issue Aug 5, 2024
@skirpichev
pythongh-122681: merge m_atan2() and c_atan2() helper functions
dc453f6
@bedevere-app bedevere-app bot mentioned this issue Aug 5, 2024
Merged
skirpichev added a commit to skirpichev/cpython that referenced this issue Aug 6, 2024
@skirpichev
pythongh-122681: remove m_atan2()/c_atan2() helpers
c096fad
@bedevere-app bedevere-app bot mentioned this issue Aug 6, 2024
Merged
vstinner pushed a commit that referenced this issue Aug 6, 2024
@skirpichev
gh-122681: merge m_atan2() and c_atan2() helper functions (#122682)
0b433aa
brandtbucher pushed a commit to brandtbucher/cpython that referenced this issue Aug 7, 2024
@skirpichev @brandtbucher
pythongh-122681: merge m_atan2() and c_atan2() helper functions (pyth…
bc422ed 
…on#122682)
kumaraditya303 pushed a commit that referenced this issue Aug 17, 2024
@skirpichev
gh-122681: remove m_atan2()/c_atan2() helpers (#122715)
19be0ee
jeremyhylton pushed a commit to jeremyhylton/cpython that referenced this issue Aug 19, 2024
@skirpichev @jeremyhylton
pythongh-122681: remove m_atan2()/c_atan2() helpers (python#122715)
a5f57ab
blhsing pushed a commit to blhsing/cpython that referenced this issue Aug 22, 2024
@skirpichev @blhsing
pythongh-122681: merge m_atan2() and c_atan2() helper functions (pyth…
094aa0b 
…on#122682)
blhsing pushed a commit to blhsing/cpython that referenced this issue Aug 22, 2024
@skirpichev @blhsing
pythongh-122681: remove m_atan2()/c_atan2() helpers (python#122715)
d7d56eb
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