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Re: [JAVA] Implement more java.lang.Math builtins.
Roger Sayle writes:
> Hi Andrew,
> On Thu, 29 May 2003, Andrew Haley wrote:
> > Roger Sayle writes:
> > > The following patch tweaks the gcj front-end to use GCC's built-ins
> > > for the mathematical functions atan, atan2, exp, log, pow and tan
> > > in java.lang.Math builtins.
> > 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.
> > Perhaps we could enable this with a switch; perhaps it doesn't matter.
> > Comments welcome...
> I'll have to double check the wording in the JLS, but I believe that
> its doesn't require anything beyond the appropriate IEEE standards,
> with the exception that IEEE FP exceptions can/are/maybe thrown as
> java exceptions.
> The default behaviour of GCC's built-in mathematical functions is to
> only apply an optimization if its guaranteed to produce identical
> floating point results without risk of overflow, rounding or exception.
> Such as calculating sqrt(2.0) or pow(2.0,3.0) at compile-time. So
> although many language standards permit up to 1 ulp error (or worse),
> GCC's middle-end requires a perfect 0.5 ulp for IEEE double by default.
Yes, but are the math functions themselves required to be within 1 ulp
of the correctly rounded result? Are they required to be monotonic?