I'm surprised this person didn't switch to using wcalc, instead of awk. For comparison:

fao_@blob:~$ time $(echo '' | awk '{print (2*-1)}' >/dev/null)

real 0m0.006s user 0m0.006s sys 0m0.000s

fao_@blob:~$ time $(wcalc '2*-1' >/dev/null)

real 0m0.005s user 0m0.001s sys 0m0.005s

I'd imagine you could use something like xargs to insert the number so that wcalc can interpret the bits for you