How do I call another function

[Billy Patton]

If I'm writing a function in XS package a function Z.
It needs to call funxtion X in package A::B
What is the correct syntax for doing so?
The function X may exist in several packages.

MODULE = XXX PACKAGE = A PREFIX=a_

int Z(class)
 char* class
CODE:
{
  RETVAL = A::B->X();
}
OUTPUT:
  RETVAL

MODULE = XXX PACKAGE = A::B PREFIX=b_

int
X(class)
 char* class
CODE:
{
  RETVAL = 1;
}
OUTPUT:
  RETVAL