Re: Draft "Unsafe fp optimizations" project description.

[dewar at gnat dot com]

<<Unfortunately, on the system he works on, the kernel traps now start to
form a noticable performance problem.
>>

Absolutely, this is a well known problem. If you look back at the thread,
you will see that very early on I suggested that sudden underflow was a
perfectly reasonable approximation for many purposes. Furthermore, my
viewpoint is that on machines where denormals are very expensive, it
is reasonable to do flush-to-zero in default mode, and reserve the
expensive denormal mode for -mieee (so in fact I go *further* than
agreeing this should be in -ffast-math :-)

But what I was saying was that casually, many programmers will not understand
why denormals are so valuable. Yes, if you are on a machine which cannot
provide this facility with reasonable efficiency, then it is reasonable
to abandon it, but many people are unaware of why this is a real loss!