[JAVA] Implement more java.lang.Math builtins.

[Roger Sayle]

Hi Andrew,
> > I'm a bit nervous about this.  The JLS is quite specific about these
> > functions and how they are to be computed, whereas (as far as I am
> > aware) gcc's builtins are not quite so well-defined.  The efficiency
> > argument is compelling, however.
>
> Yes, but are the math functions themselves required to be within 1 ulp
> of the correctly rounded result?  Are they required to be monotonic?

I've also thought of another compromise.  To support systems with
broken or old system libraries whose -lm functions aren't guaranteed
to be with 1ulp and/or monotonic, the builtins mechanism in the java
front-end could be rewritten so that GCC's built-in's don't fall
back to libm calls, but to their Java name-mangled equivalents.  This
way the java runtime's implementations are always used, and constant
folding turns java.lang.Math.pow(x,0.5) into java.lang.Math.sqrt(x)
instead of _sqrt(x).

This would require a significant rework such that java/builtins.c uses
a similar mechanism to g77's com.c rather than using builtins.def.  If
you think this is preferrable, I can submit a suitable follow-up
patch.

Roger
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