Parallel Programming Guide for HP-UX Systems

Troubleshooting
Floating-point imprecision
Chapter 9 185
Enabling sudden underflow
By default, PA-RISC processor hardware represents a floating point
number in denormalized format when the number is tiny. A floating
point number is considered tiny if its exponent field is zero but its
mantissa is nonzero. This practice is extremely costly in terms of
execution time and seldom provides any benefit.
You can enable sudden underflow (flush to zero) of denormalized values
by passing the +FPD flag to the linker. This is done using the -W compiler
option.
For more information, refer to the HP-UX Floating-Point Guide.
The following example shows an f90 command line issuing this
command:
%f90 -Wl,+FPD prog.f
This command line compiles the program prog.f and instructs the
linker to enable sudden underflow.