Csaba Hruska
Hello,
I've discovered that the remAddr# primop documentation is inconsistent with the implementation. According to the docs (primops.txt.pp) the remAddr# should be the same as remInt#.
primop AddrRemOp "remAddr#" GenPrimOp Addr# -> Int# -> Int# {Return the remainder when the {\tt Addr\#} arg, treated like an {\tt Int\#}, is divided by the {\tt Int\#} arg.}
But it is implemented with the mo_wordURem instruction, just like the WordRemOp primop.
GHC/StgToCmm/Prim.hs:
AddrRemOp -> \args -> opTranslate args (mo_wordURem platform)
WordRemOp -> \args -> opTranslate args (mo_wordURem platform)
IntRemOp -> \args -> opTranslate args (mo_wordSRem platform)
Which one is correct, the docs or the implementation?
That is a good question. The only user (in the GHC tree) is GHC.Ptr.alignPtr which appears to want the Word semantics (that is, it would break given a negative remainder). Moreover, my mental model of pointers is that for the purposes of arithmetic they are non-negative. Therefore, I belive that the documentation here is wrong. I have opened #19332 to track this. Cheers, - Ben