This is the mail archive of the gcc@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]

Re: Draft "Unsafe fp optimizations" project description.


<<I don't think the abrupt underflow settings which Itanium and
P4 architectures depend on for good performance qualify as
"denormal orthodoxy."  Do the literature treat the combination
of abrupt underflow with extended exponent range?
>>

At least one paper I read way back did discuss this issue, but I can't 
remember where I found it (that was back when I was writing my book,
by the way, I still think that chapter 5 of that book, Microprocessors
A Programmer's View, is a nice simple intro to some of the intracacies of
IEEE, and in particular it discusses why denormals are so important.

I think it is overstrong to say that the Itanium and P4 architectures
depend on abrupt unberflow for good performance, do you have figures to
back up this claim.

Please do not assume that the presence of these options means they are
useful necessarily (if you thought that, you might even end up using the
ENTER instruction, which was a bad idea even way back on the 386 :-)

Nothing substitutes for measurements when it comes to arguing the
actual value of optimziations!


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]