replace itrunc(Uint8, 1234) => mod(1234, Uint8), etc. [fix #8646]

Here's the proposal I put forth in #8646 to replace `itrunc(Uint8, 1234)` etc. with `mod(1234, Uint8)`. Not necessarily how we want to do this, but at least it (hopefully) identifies all the places in base where this needs to be changed.
you missed an itrunc on line 172