#!/usr/bin/env python
# encoding: utf-8


__all__ = ['gcd']


def gcd(a, b):
    """Compute gcd(a,b)

    :param a: first number
    :param b: second number
    :returns: the gcd

    """
    pos_a, _a = (a >= 0), abs(a)
    pos_b, _b = (b >= 0), abs(b)

    gcd_sgn = (-1 + 2 * (pos_a or pos_b))

    if _a > _b:
        c = _a % _b
    else:
        c = _b % _a

    if c == 0:
        return gcd_sgn * min(_a, _b)
    elif _a == 1:
        return gcd_sgn * _b
    elif _b == 1:
        return gcd_sgn * _a
    else:
        return gcd_sgn * gcd(min(_a, _b), c)

if __name__ == '__main__':
    print(gcd(3, 15))
    print(gcd(3, 15))
    print(gcd(-15, -3))
    print(gcd(-3, -12))


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