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Re: Non-deterministic numerical inaccuracies in

  • To: mathgroup at smc.vnet.net
  • Subject: [mg94965] Re: Non-deterministic numerical inaccuracies in
  • From: David Bailey <dave at removedbailey.co.uk>
  • Date: Thu, 1 Jan 2009 07:26:41 -0500 (EST)
  • References: <gjfjuo$dan$1@smc.vnet.net>

Bob Hanlon wrote:
> $Version
> 
> 7.0 for Mac OS X x86 (64-bit) (November 11, 2008)
> 
> No problem apparent.
> 
> 
> Bob Hanlon
> 
> 
> On Tue, Dec 30, 2008 at 12:26 PM , Sjoerd C. de Vries wrote:
> 

I think I might be able to guess what this is connected with. 64-bit C 
will use the XMM registers for floating point. These are 64-bits in 
length. 32-bit C has to cater for much older hardware, and so will use 
the old coprocessor registers. These are 80-bits in length. If the 
kernel contains some code that saves these registers as 64-bit numbers - 
say in response to a random interupt - this will truncate the extra bits 
when they are restored and make a tiny change in certain circumstances.

It would be interesting if someone at WRI would tell me if I have 
guessed correctly!

David Bailey
http://www.dbaileyconsultancy.co.uk


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