UNDERFLOW is enabled throughout the program, except within
the scope of the NOUNDERFLOW condition prefix.
Result
The invalid floating-point value is set to 0 except for IEEE floating-point on z/OS when the result is undefined.
Cause and syntax
The UNDERFLOW computational condition is raised when the magnitude
of a floating-point number is smaller than the minimum allowed.
save UNDERFLOW is not raised when equal numbers are subtracted (often
called significance error).
The expression X(-Y) (where
Y>0) can be evaluated by taking the reciprocal of XY;
hence, the OVERFLOW condition might be raised instead of the UNDERFLOW condition.
Unless the exception is raised while evaluating an IEEE floating-point expression (in either binary or decimal) on z/OS,
a message is printed, and
execution continues from the point at which the condition was raised;
if raised while evaluating an IEEE floating-point exception on z/OS,
a message is printed and the ERROR condition is raised.
Normal return
Unless the exception is raised while evaluating an IEEE floating-point expression (in either binary or decimal) on z/OS,
control returns to the point immediately following the point at which the condition was raised;
if raised while evaluating an IEEE floating-point exception on z/OS,
the ERROR condition is raised.