Re: Does this model work ?

[jrcarter001@my-dejanews.com]

In article <7hmda1$khp$1@nnrp1.deja.com>,
  Robert Dewar <robert_dewar@my-dejanews.com> wrote:
> However, Ada is no panacea. Over and over again, we run into
> cases where incompetence or deliberate (in-retrospect-poort)
> decisions have lead to highly non-portable code, and this can
> often be eacerbated by management or incompetent Ada vendor
> sales people who have sold the idea that Ada guarantees
> 100% portability. That's wrong, it does not.
>

I'd like to make a plug for Ada over Ada 83 for portability. Ada 83
could be used to produce highly portable programs, but in some arenas
led to lack of portability. As an example, I recently got to port some
Ada-83 real-time code from a little-endian processor to a big-endian
processor. In the process, I could convert it from Ada 83 to Ada.

The code has timing requirements, and the Ada-83 compiler had problems
with low-level bit manipulation. Converting to Boolean arrays was too
slow, so C functions were used for bit manipulation. Much of this C code
was endian dependent.

This was a portability problem that could have been avoided.

More significantly, the Ada tasking implementation did not allow them to
use tasks and meet their timing requirements, leading to OS calls for
task-related operations. This was not a portability problem, since both
versions would use the same RTOS, but could become one.

Ada now has low-level bit-manipulation capabilities through modular
types and package Interfaces, and protected objects have eliminated much
of the overhead that made Ada tasking too slow in Ada 83. I was able to
create a completely portable version of the code that ran on
little-endian and big-endian machines with different OSes, met the
timing requirements, and gave identical results.

Timing seems to be becoming a moot point. This code has since been used
successfully on a 133 Mhz Pentium laptop running Windows 95 with a
custom PCMCIA card. This duplicates the functionality of the custom
hardware that the code originally ran on, except the custom hardware
could provide 4 communications channels, and the PCMCIA card only
provides 2. This laptop/PCMCIA combination promises to be a popular
product for our company.


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