from .math_rational_rational import rational_parts
from .math_rational_types import Rational


def compare_rational(a: Rational, b: Rational) -> int:
    """-1, 0 or 1. Exact: cross-multiplied, never through a float."""
    an, ad = rational_parts(a)
    bn, bd = rational_parts(b)
    left = an * bd
    right = bn * ad
    return -1 if left < right else 1 if left > right else 0