[M3devel] extended

[Peter McKinna]

Hi

  While we are on the subject of integer types can we diverge slightly to
floating point types. I wonder if anyone can explain why the extended type
is treated exactly the same as longreal in the frontend? They have the same
sizes and ranges and precisions.
  As for backends,  at the moment m3cc is generating 8 byte sse
instructions for both types. The llvm is generating 10 byte float
instructions as per its x86fp80 type which are a fair bit slower at the
expense of greater range and precision. However they are not interoperable
with legacy libraries and we should probably change the type to agree with
m3cc and the frontend.
  It seems that the 8087 80 bit float is being phased out see
http://csapp.cs.cmu.edu/2e/waside/waside-x87.pdf
so maybe the m3 implementors saw the writing on the wall and and decided to
wait for hardware to catch up. Anyway I wonder if its worth considering
making extended one of the 128 bit floating point types which although
emulated in software would at least give us a different type and one which
would give some applications a huge precision (and range ~10^4090) boost.

Peter
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