Re: [Boost-users] Boost.Numeric.Interval: Please specifyrounding control mechanism.

From: Guillaume Melquiond (guillaume.melquiond_at_[hidden])
Date: 2007-03-15 06:35:14

Quoting John Maddock:
> BTW I believe recent Intel Win32 compiler releases do the same thing for x86
> as well (which is to say they don't use the x87 instructions just the SSE
> ones).  But maybe someone more knowledgable will step in and comfirm this:
> or maybe it makes no difference?

It makes a big difference for the interval library. For performance 
reason, the
library tries to setup only the coprocessor that will perform the
floating-point computations. So if its assumptions are wrong, 
computations will
be performed on a coprocessor that was not properly configured. In 
contrast, the
fesetround C99 function usually reads and writes the control register of every
coprocessor. Needless to say, that will bring the machine to a halt, 
that's why
the library tries to avoid it as much as possible (not withstanding the fact
that it is not available everywhere).

Best regards,

Guillaume