Petr Viktorin <encu...@gmail.com> added the comment:
C compiler dev that it's indeed undefined behavior.
> Quick and obvious fix:
>
> static PyObject *
> nu_bool(const char *p, const formatdef *f)
> {
> char x;
> memcpy((char *)&x, p, sizeof x);
> return PyBool_FromLong(x != 0);
> }
>
> Which is optimized to
>
> static PyObject *
> nu_bool(const char *p, const formatdef *f)
> {
> return PyBool_FromLong(*p != 0);
> }
I'm left with a question for CPython's struct experts:
The above would be my preferred fix, but the Python code is asking to convert a
memory buffer to bool *using platform-specific semantics*.
Is this fix OK if C treats a \xf0 _Bool as falsey?
(Also, this assumes size of _Bool is the same as size of char.
I guess we can add a build-time assertion for that, and say we don't support
platforms where that's not the case.)
----------
nosy: +mark.dickinson, meador.inge
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<https://bugs.python.org/issue39689>
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