cleanup/perf: simplify a few expressions

[gthb]

Simplify/optimize a few expressions a tiny bit, based on these facts:

• dividing by X ** exp is the same as multiplying by X ** -exp
• multiplication is a little faster than division (at least on the metal — with transpilation and a VM underneath you, who knows?)
• inside if (places), the expression places || 0 is equivalent to places