Re: Singular Value Decomposition (SVD) Ada Algorithm

[jpwoodruff@irisinternet.net (John Woodruff)]

aschwarz@acm.org (skidmarks) wrote in message news:<35f054ea.0411010817.52bbf8fc@posting.google.com>...

> > <...> I developed a doubly-linked list. 
<...>

I guess since I might have induced you to show us your thinking, it's
proper I offer my remarks.


> 1. Optimization of data via generics was avoided. All data is 32-bits.
>    The rationale is:
>    a. If size optimized and packed, more instructions are required
>       during operation for (un)packing operations, which increases
>       total size, and with more instructions there is decreased
> performance.
>       (The size is relative and depends on use. Performance is bad.)
>    b. If size optimized and unpacked, then depending on the CPU, slack
>       bytes are added which increases the size.
>    c. By making all sizes the same, the issue becomes movement into
>       and out of the fixed size datum field.

Let me say that I have no idea what requirements you're working to. 
If you're working in a context with a few tens of kilobytes of memory,
or with a 100 Khz processor, or the like, I can sympathize with your
effort to crowd every last particle of performance.

However in my own life, I have stuck with an aphorism on the topic of
optimization that I picked up 30 or so years ago:
There are two guidelines for micro-optimization:
   -- Don't do it
   -- Don't do it yet.

<...>

> The final result is that there
> is a division of responsibility which (I believe) provides an adequate
> level of encapsulation and information hiding while giving some
> application level conveniences. 

My thought is that you have not encapsulated quite as much as you
might have done.  At the outset, you said "All data is 32-bits".  But
I can think of *a lot* of data that don't comply.  And your list
handler doesn't cover those.  So someday you might need to repeat the
effort you expended in order to build a new one.  Or, even worse, you
or your successor will forget the restrictions and reuse your list
manager with a non-32bit-compliant component, and the result might not
be pretty.

My committment to software engineering was (before I retired) to try
to leave lasting artifacts that will function for *decades* in
evolving service.  The tactics that Ada promotes helped me do that, I
think.  Other folks have other goals, I guess

> There is always room for comment and architectural changes. A dialog
> will always be appreciated.
>

I enjoy the occasional dialog!
John