sparc assembly and the %y register

Question

I am currently working with a sparc computer and I am trying to know if a number is prime or not.

here is a part of the code :

     mov  0,%y   
     mov  3, %l1
     nop
     nop
     nop

     sdiv %l1,2,%l3
        rd      %y, %l6   
     cmp  %l6, 0

So basicaly what we have here is 3/2. So there should be a reminder of 1. This reminder should be putted in the %Y register. But When I look at %Y, it is still at 0. Why is %Y still at 0 while it should show me a reminder of 1?

Answer 1

According to the SPARC Architecture Manual, page 116, it's an implementation option whether or not to set %y in sdiv. Apparently, it's also an implementation option whether to implement it in hardware or software, so it seems that some software implementations don't set %y.