import math


def blendSinc(d, u=1.0):
    """
       blending function sinc
       d = delta x = x - horizontal shift
       u = uncertainty radius of xabs estimate error

       returns blend
    """
    u = float(u)

    if d == 0:
        return 1

    if u == 0:
        raise ValueError("Params cannot be zero.")

    mu = math.sin(d/u) / (d/u)

    return mu if mu >= 0 else 0