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Re: fpu/e_expl.c for i686
Stephen L Moshier <email@example.com> writes:
> > +__ieee754_expl (long double x)
> > ...
> > + "fldl2e\n"
> > + "fmulp\n" /* x * log2(e) */
> > + "fld %%st\n"
> > + "frndint\n" /* int(x *> log2(e)) */
> > + "fsubr %%st,%%st(1)\n" /* fract(x * log2(e)) */
> This code seems adequate for double precision but it has poor
> accuracy for long double, due to error amplification over the
> wider domain of the long double function. For example, expl(1000)
> is off by roughly 460 ulps. I would suggest improving the range reduction
expl (1000) is .19e435 and can only be represented with long doubles.
How much would the error be for expl (100)?
> method here, but since that entails three or four more multiplications
> you might not want to make the speed sacrifice. What would your
> policy be about this tradeoff of speed versus accuracy?
I personally would go for accuracy.
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