VADS 8-byte component alignment constraint

VADS 8-byte component alignment constraint

[Britt Snodgrass]

I'm attempting to port some avionics data processing code from an HP
9000/380 (68040 CPU) to an HP 9000/735 (PA-RISC CPU) (both running
HP-UX Unix) and to an i486 PC (running Windows NT "3.1").  The Ada
compiler is VADS 6.0 on the 9000/380 and VADS 6.2 on the other two.

Code that compiles and runs on the 9000/380 results in "component
must be aligned on a 8 byte boundary" error messages when compiling
certain record structures on the other two machines.  I initially
thought this was something due to the RISC processor but VADS for the
Intel processor has the same constraint.

In general I can't get around this by padding the record structures
because the record has to exactly match the data records on disk. I am
forced to read the data into a Boolean array of the proper length and
then map the Boolean bits to the original record using address
representation clauses.  This is a really ugly way to code but I
haven't found a better solution.

Has anyone else encountered this problem and is there a semi-elegant
workaround?


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Capt Britt Snodgrass e-mail: britt@madrid.46tg.af.mil
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