Moving VAX into 21 century :-)

[Anders Magnusson <ragge%ludd.ltu.se@localhost>]

Hi all,

I have been looking at some VAX problems lately, and have found out that 
there are two architectural things things that probably would help VAX 
quite much.

1) Change calling convention.
    As described in my previous mail, it would solve a very old 
well-known performance problem.

2) Make VAX use IEEE floats :-)
    Today virtually no floating point exist that is not IEEE.  The only 
fragment around is probably the VAX floats.

    I have done some checking, and if we accept the difference in 
rounding (VAX uses a different way than IEEE) then it would be (almost) 
no overhead in the common cases (overhead comes when dealing with INF, 
NAN and subnormals).
    - Use F and G floats.  They have the same format as IEEE single and 
double, and are both available on virtually all VAXen.
    - Make use of the floating point faults that VAXen can generate to 
emulate the features missing on VAX.

    ...in theory also H floats could be used as long double since they 
match the IEEE 128-bit quad precision :-)
       But since H float is optional it might end up being emulated 
(maybe not a big problem?)

Comments on this?

-- Ragge