[meindnoch]

By the way, there's another function that can be used to turn multiplication into addition: f(x) = x^2 / 2

a * b = f(a + b) - (f(a) + f(b))

[secondcoming]

Isn’t x^2 a multiplication?

[meindnoch]

No, you misunderstood what I meant.

Normally, a sliderule at distance x has the value of log(x) written on it, which allows doing multiplications by moving along the sliderule, since log(ab) = log(a) + log(b).

Now imagine a sliderule onto which values of x^2/2 are written. This also allows you to multiply two numbers, because ab = (a+b)^2/2 - (a^2/2 + b^2/2).