libjava configure question

Thu May 26 19:02:00 GMT 2005

Andrew Haley writes:
 > Bryce McKinlay writes:
 > > Andrew Haley wrote:
 > > 
 > > >Tom Tromey writes:
 > > > > >>>>> "Andrew" == Andrew Haley <aph@redhat.com> writes:
 > > > > 
 > > > > Andrew> One other thing: I don't think we can do this in
 > > > > Andrew> general and meet even the more relaxed requirements of
 > > > > Andrew> java.lang.Math, because the x86 has a restricted range
 > > > > Andrew> of allowable arguments to its trig functions.
 > > > > 
 > > > > I thought the Math restrictions were designed to explicitly allow use
 > > > > of the FPU on x86.
 > > >
 > > >Yes, but not without some wrapper code. The crucial issue here is
 > > >full range reduction, and the floating-point instructions don't do
 > > >that by themselves.
 > > 
 > > I'm sure the math library functions do, though - we'd still likely
 > > get a performance improvement from using those directly, even
 > > without inlining of FP instructions - since they'll be optimized
 > > for each architecture.
 > 
 > Yes, that's probably true. We'd have to make sure that calls to
 > java::lang::Math::sin() etc. were replaced by sin() and we'd also have
 > either to remove our own definitions of the functions or make them
 > weak.
 > 
 > All quite possible, but perhaps not top of the list.
I just tried, and I discovered that even without any optimizations
gcc/glibc fails dismally to meet even the relaxed java.lang.Math
accuracy requirement for trig functions. We should keep our own math
library, because it's better.
Andrew.