@cython.cdivision(True) causes "math domain error" in weird scenario

Running a Jupyter notebook in VSCode, I am getting bizarre behavior with the Cython unprotected division directive. Starting the session with %load_ext cython, run:

%%cython
import math
cimport cython

@cython.cdivision(True)
def simpleTest(int d):
    cdef double c = 1/math.exp(math.log(math.sqrt(2/d)))
    return c

Now run simpleTest(x) and for any value of x >= 3 I get:

ValueError: math domain error

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But running without the @cython.cdivision(True) directive it works fine for all x > 0, as it should. Why does the directive break this calculation? Is there a better approach?

>Solution :

You are telling Cython to divide like in C. In C, integer division produces integer results, rounding toward 0.

With C division, 2/d is 0 for d > 2. You are trying to take the logarithm of 0.