Thread: pthread safe library functions?

In linux using pthreads
When I call a whatever usual function like for instance:

thread 1
a=div(b,c).rem

thread 2
x=div(y,z).rem

so I call the same function on different (not shared) data
Can I be sure that the two function calls by the two threads do not share any (internal) data (may be registers or global-library-shared) and so have no side unpredicted effect??

The same question holds for usual functions like sin() exp() pow() rand() nanosleep() etc.