about godabil piety

[curiousman]

I know random2(num) function is 0 to num-1

but i can't understand screenshots

piety cost fomula is
val + random2((val + 1) / 2 + 1)

and makhleb's greater servant value is 5

my calculation is 5+random2(4)

so result is 5~8

but it's not real

ingame experiment result is 4~7

what is my mistake?

I'm confused ...

I feel like golden eyes victim

[Sandman25]

Ignore the comment and check source code. It is
const int piety_cost =
_scale_piety_cost(abil.ability, abil.piety_cost.cost());