Fixed point matrix representation considered harmful

[Daniel Stone]

On Thu, Mar 20, 2008 at 07:10:59PM +0100, Marc Balmer wrote:
> Daniel Stone wrote:
>> On Thu, Mar 20, 2008 at 06:48:23PM +0100, Joerg Sonnenberger wrote:
>>> On Wed, Mar 19, 2008 at 09:55:34AM -0700, Keith Packard wrote:
>>>> On Wed, 2008-03-19 at 16:59 +0100, Joerg Sonnenberger wrote:
>>>>> OK, so you basically want to specify a 32bit (or whatever) IEEE format
>>>>> without all the nasty parts? E.g. subnormals and exception values?
>>>> Exception values (NaN, +/-inf) should be invalid, but denorms shouldn't
>>>> cause any issues for us.
>>> Except that it complicates decoding for non-IEEE platforms. Think VAX.
>>
>> Are we actually designing for VAX these days? There aren't many other
>> non-IEEE platforms that I know of: even lame embedded/consumer chips are
>> pretty much all IEEE now, TTBOMK.
>
> Of course...  The BSDs run happily on Vaxen and a Vax still deserves
> a modern operating system and a decent graphics environment.

Right.  If it's impossible to do it on VAX, then that's an issue.  If
it's _hard_ to do on a VAX ... well, so is everything else.  Life's
tough on marginal platforms.

There's a huge difference between designing to include all platforms,
and optimising for ridiculously tiny corner cases (of which VAX is one:
how many are still in use by people who wish they could do arbitrary
transforms in software, compared to others?).

> The world is not all IEEE, as much as it is not Linux/i386 only..;)

A vastly more significant portion of the world is non-Linux/i386/x86_64
than non-IEEE.

Cheers,
Daniel
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