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Re: floating point war casualty list


Excerpt of message (sent 28 May 2002) by Alan Lehotsky:
> If I recall correctly, there are TWO (or more) PDP-11 floating point 
> formats.  I think it
> had something to do with word-order for the double-precision FP, but 
> since it's been
> close to 25 years since I last did anything with the PDP-11 my memory 
> is somewhat
> fuzzy.

Yes, there are two formats, which match the F and D formats of the
vax.  The first 32 bits are the same; the D format adds another 32
bits for low order mantissa.

The pdp11 gcc target can produce either with -mfloat32 or -mfloat64.
I reported earlier that VAX_FLOAT_FORMAT makes it come out right --
interestingly enough, that's true only for D.  The F format is wrong
in my tests, don't know why yet.

   paul


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