In reply to Peter Lancashire.

Thanks for your comments. Yes, in many cases SAS returns a missing value when it encounters an overflow (or underflow). For example, the following program returns a missing value for EXP(800) and writes a note to the log:
NOTE: Invalid argument to function EXP(800) at line NNN column 7.

data Compute;
input x @@;
exp = exp(x);
datalines;
600 700 800
;
proc print data=Compute;
run;

However, sometimes programmers want to trap invalid input arguments BEFORE they operate on them.