On Sat, 2005-06-18 at 17:37 -0400, Robert Dewar wrote: > > Changing the default rounding of the processor will make code less > > efficient?
> Yes, if you have to change it backwards and forwards for float and > double Quite rare. Only usage I've seen is for tabulation when you want to save storage space but there it won't be an issue since you're explicitely storing to memory. > ... and if you insist on getting the range right as well as > the precision, then you have to do extra stores. If you code run in extra range issue then you'll get "expected" results on x86 and it will fail everywhere else, a nice way to detect those issues indeed (and you won't face this if you developped your code on non x86). > Changing the rounding mode alone does not give what people call IEEE behavior. I agree, but in 99.9% of the case it will do what people expect. For the remaining 0.1% of the case, we're facing expert code and experts can look into the magic manual and find the right flags/pragma/libraries/whatever :). Anyway, default situation is unlikely to change, and x86_64 ABI default to SSE2 plus it will soon be hard to find reasonably powerful x86 only harware out there... Laurent
