[Numeric-interest] interesting report on Mac x86 rounding directions

[David Hough 754R work]

I don't know any more than what's here:



Subject: 	[Reliable Computing] Rounding Control doesn't work on MacBook
Date: 	Mon, 03 Dec 2007 09:21:25 +0000
From: 	John Pryce <j.d.pryce at ntlworld.com>
To: 	reliable_computing at interval.louisiana.edu



Dear Intervallers

I bought a MacBook Pro laptop in Spring 2007, with the Intel dual-
core processor. I intend to use it for research in interval
computation. But Rump's INTLAB, on startup, said "Sorry, can't switch
rounding mode".

So I wrote a simple C program using the fesetround() and fegetround()
functions mandated by the C standard (N1124), and ran it with GCC
4.0.1. The output indicates (a) one can't change rounding mode and
(b) it is set to "round towards zero", i.e. archaic chopping.

I can believe (a) might happen with GCC, but I cannot believe (b).
Can anyone shed light on this and tell me a workaround, so I can do
real interval work on my elegant machine?

My apologies if you have had multiple postings of this query.

John Pryce
j.d.pryce at ntlworld.com