IEEE 754-1985 and Intel 8087
(Let's not misuse a "Subject:" reserved for voting!)
The Intel chip did come out before the standard, and indeed there were
several deviations, some of which got corrected in later versions.
One of the issues that got settled late was the decision to support
only one kind of infinity, signed affine infinity, and to drop the
unsigned projective infinity. There were also changes with respect
to NaNs and so-called "pseudo-subnormal" entities (if I can trust my
memory; my "8087 book" is at home and I'm not).
The whole thrust of the Kahan-initiated effort was however to enshrine a
complete set of floating-point primitives, not just common practice which
at the time was a scattered set of incompatible formats and features.
Here I want to stress "complete" -- precisely to avoid that missing but
needed features would be implemented in diverging and incompatible ways.
It is true that some things were overspecified and thus never fully
supported, such as the exception model (which may have been adequate
in its time but is problematic in today's multicore world), and others
were underspecified and thus led to incompatibilities which 754-2008
had to carry along -- but on the whole I think it was rather successful.
To get back to Motion 8: this is 1788's attempt at laying the proper
foundations for exception support. SOMETHING is needed, and so the
issue CANNOT be deferred to a "revised 1788" -- otherwise we will end
up with grossly-incompatible disjoint "solutions".
Michel.
---Sent: 2009-11-23 19:42:42 UTC