Re: Fast FEXP approximation

Ian Osgood <iano@[EMAIL PROTECTED]
> wrote:
> I recently ran across a fast approximation for exp() which relies on
> the internal structure of IEEE doubles, implemented as a cast integer
> multiply by a magic constant. Is this already known to the Forth
> community?

Surely it's just a polynomial approximation to exp(x), with order 1
and 0.5 <= x < 1; it can't be that, though, because it would be
nowhere near accurate enough.  

I an see why a right ****ft of an IEEE double with a little diddling of
the low-order bits would be roughly there.  How rough an approximation
is this?  :-)

Tang's algorithm is fast, but there's a bit more to it than just a
multiply.  Can't be that.

OK, go on, tell us...

Andrew.