cyberkm

x * 0x0101010101010101ull

is equal to (x + (x<<8) + (x<<16) + ... + (x<<56)) 

cyberkm

Source: https://www.johndcook.com/blog/2018/09/26/polygon-area/

Shoelace formula:
x1 y2 + x2 y3 + … xn y1 – y1 x2 – y2 x3 – … –  yn x1

Python implementation
def area(x, y):
        n = len(x)
        s = 0.0