[issue45440] [C API] Py_IS_INFINITY() macro doesn't work in the limited C API if isinf() is not defined

[STINNER Victor]

New submission from STINNER Victor <vstinner at python.org>:

If the HAVE_DECL_ISINF macro is not defined in pyconfig.h, the Py_IS_INFINITY macro is defined as:

#define Py_IS_INFINITY(X) \
    ((X) && (Py_FORCE_DOUBLE(X)*0.5 == Py_FORCE_DOUBLE(X)))

Problem: Py_FORCE_DOUBLE() is excluded from the limited C API (and the stable ABI).

I see different options:

* Implement Py_IS_INFINITY() as an opaque function if the HAVE_DECL_ISINF macro is not defined. I did something similar in Py_INCREF() to support the limited C API with a debug build of Python: call _Py_IncRef() opaque function.

* Make Py_FORCE_DOUBLE() private and add it to the limited C API as an implementation detail.

* Add Py_FORCE_DOUBLE() macro to the limited C API: the current implementation is fragile, it depends on how Python.h is included. Also, I dislike macros in the limited C API.

I would prefer to *remove* Py_FORCE_DOUBLE() to all APIs, than adding it to the limited C API.

----------
components: C API
messages: 403704
nosy: vstinner
priority: normal
severity: normal
status: open
title: [C API] Py_IS_INFINITY() macro doesn't work in the limited C API if isinf() is not defined
versions: Python 3.11

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue45440>
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