Bug report

Bug description:

https://github.com/python/cpython/blob/main/Objects/complexobject.c#L150 _Py_c_pow() contains:

        at = atan2(a.imag, a.real);
        phase = at*b.real;
        if (b.imag != 0.0) {
            len /= exp(at*b.imag);

An oss-fuzz pycompiler fuzzer identified a problem compiling the code " 9J**33J**3" within the optimizer folding the constant by doing the math in place. We haven't been able to reproduce this ourselves - but code inspection reveals a potential problem:

C exp(x) can return 0 in a couple of cases. Which would lead to the /= executing an undefined division by zero operation.

I believe the correct _Py_c_pow() code should look something like:

        if (b.imag != 0.0) {
            double tmp_exp = exp(at*b.imag);
            if (exp == 0.0 || errno == ERANGE) {
                // Detected as OverflowError by our caller.
                r.real = Py_HUGE_VAL;
                r.imag = Py_HUGE_VAL;
                return r;
            }
            len /= tmp_exp;

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-113841: fix possible undefined division by 0 in _Py_c_pow() #127211
• [3.13] gh-113841: fix possible undefined division by 0 in _Py_c_pow() (GH-127211) #127216
• [3.12] gh-113841: fix possible undefined division by 0 in _Py_c_pow() (GH-127211) (GH-127216) #127530