Re: rational to floating point?

Thant Tessman <thant@acm.org> writes:
|>
|> I haven't had time to give the above the full attention they deserve,
|> but I think I have a handle on how to produce the significand and
|> exponent of the floating point number (as arbitrary-precision integers
|> (conveniently in base 256 in my implementation)). What's missing is
|> the conversion to the actual float. The Clinger paper makes use of a
|> mysteriously unexplained "make-float" function, for which there seems
|> to be no portable manifestation. Things like radix conversion are no
|> sweat, but bit twiddling is not something I've had a lot of experience
|> with. Is it typical in these situations to produce the IEEE 754 float
|> bit pattern directly? If so, do I have to worry not only about whether
|> that's the standard on the chosen platform, but also about things like
|> endianness?
|>
|> [Yes, one typically twiddles the bits directly, and you have to be aware
|> of endianness. Fortunately, these days the only popular formats are
|> big- and little-endian IEEE and maybe legacy IBM hex. -John]


You have forgotten Intel 80-bit format :-)


And remember that there are several variants of IEEE - e.g. whether
denormals are supported. But they are all subsets, except for
extended precision.


Regards,
Nick Maclaren.

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