Re: Ada Portability

[knoll@coopn1.csc.ti.com (Ed Knoll @(719)593-3762)]

The issue of portability is indeterminate if it is not planned for.  There 
are some aspects of the language and of some of the compilers that can make it 
difficult.  However, we have had some fairly decent success.  For example:

  A group I was working with was supporting two programs simultaneously.  One
  job was essentially a subset of the other with about 20% unique material.
  They were both hosted on the same target (embedded processor), but each 
  program was using a different run-time library.  This was the target 
  environment.

  On the host, we were using two different compilers.  One would generate
  code for the host and the target, the other just generated code for the
  host.  The host only compiler was somewhat faster and had a better host
  debugger.

  In addition, there was a large simulation (written in FORTRAN and Pascal)
  that emulated different aspects of the environment and the system.  We
  wished to test some of the subsystems of the Ada code by substituting
  them for their counterparts in the simulation.  At the same time we were
  putting together an environment where the entire applications software
  would be driven by the environment and hardware components of that
  simulation.

  We constructed an OS frontend to hide the differences between the two
  run-times for the target and we built a body for the frontend that would 
  allow the applications to run on the host.  The host only Ada compiler
  did not include 'long_int' in the standard package because 'integer' was
  long to begin with.  A package was constructed which contained a 'long_int'
  declaration for the host; the same package contained nothing for the target.
  This package was 'with'ed and 'use'ed by everyone.  Driver packages were 
  written for the different interfaces with the simulation.

  Library organization controlled how we constructed the different versions.

  Summary: Compilers             - 2
           Platforms             - 2 (target and host)
           Operating Systems     - 3 (two target and host emulation)
           Execution Environment - 5 (standalone host, subsystem w/ simulation, 
                                      entire system w/ simulation, two targets)

Not all code was (or could) be evaluated in every environment, but much of 
it was with very few portability problems.  It did take some planning and 
some rework, but very cost effective overall.

-------------------------------------------------------------------------------

Edward L. Knoll                     Disclaimer:  If my company doesn't trust
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