HP Fortran Programmer's Reference (September 2007)

Data types and data objects

Resolving issues with unaligned data

Chapter 5136

/opt/fortran90/bin/f90 foo.f -lunalign

NOTE Nothing new is required to use the aforementioned -lunalign runtime ﬁx

approach; however, you do need the latest patch for the +allow_unaligned

compile ﬂag.

If the misaligned data might be passed to routines which are not compiled with

+allow_unaligned (for example, Fortran runtime IO and F90 libraries), then having the call

will allow the runtime ﬁxes to happen which will prevent bus errors in your application.

To realize optimum performance, try and measure the following two options:

1. Compile with +allow_unaligned and insert the call to allow_unaligned_data_access()

2. Only insert the call to allow_unaligned_data_access()

Option #1 may perform faster with very few references to misaligned data and a handler is

invoked for these misaligned references. #2 may perform faster with many references.