In programming, a call site of a function or subroutine is the location (line of code) where the function is called (or may be called, through dynamic dispatch).
A call site is where zero or more arguments are passed to the function, and zero or more return values are received.
[1][2] IBM/360 or Z/Architecture In some occasions, return is an efficient method of indicating success or failure.
requiring code, for example a small branch table, at the return point - to go directly to process the case (as in HLL Switch statement).
Conventionally however, a return code is set in R15 (0=OK, 4= failure, or similar ..) but requiring a separate instruction to test R15 or use directly as a branch index.