Segmentation fault when using multiply

[Popeyef5]

• OS: linux
• Python Version (python --version): Python 3.8.13
• Environment (output of pip freeze): argcomplete==1.12.3 attrs==21.4.0 cached-property==1.5.2 certifi==2022.5.18.1 cytoolz==0.11.2 eth-hash==0.3.2 eth-typing==3.0.0 eth-utils==2.0.0 hypothesis==6.46.11 iniconfig==1.1.1 mypy-extensions==0.4.3 numpy==1.22.4 packaging==21.3 pandas==1.4.2 pipx==0.16.4 pluggy==1.0.0 py==1.11.0 py-ecc==6.0.0 pyparsing==3.0.9 pytest==7.1.2 python-dateutil==2.8.2 pytz==2022.1 six==1.16.0 sortedcontainers==2.4.0 tomli==2.0.1 toolz==0.11.2 userpath==1.7.0

What is wrong?

'Segmentation fault (core dumped)' error when doing

multiply(G1, -1)

On bn128. Happened with the few other negative numbers I tried. Did not try with other curves, I assume the problem persists because -1 // 2 = -1 and the recursive nature of the multiply function.

How can it be fixed

This fixes it:

def multiply(pt: Point2D[Field], n: int) -> Point2D[Field]:
    m = abs(n)
    if m == 0:
        ret = None
    elif m == 1:
        ret = pt
    elif not m % 2:
        ret = multiply(double(pt), m // 2)
    else:
        ret = add(multiply(double(pt), int(m // 2)), pt)
    if n < 0:
        ret = neg(ret)
    return ret

alternatively this should work as well but might be less efficient:

def multiply(pt: Point2D[Field], n: int) -> Point2D[Field]:
    n = n % field_modulus
   # rest of the function still the same

Could write up a quick PR if this indeed works.