On Thu, 20 Sep 2007 16:49:47 EDT, [EMAIL PROTECTED] said: > The same problem should exist on a regular PC running on a Core 2 > processor with XP. XP running natively on an Intel Mac really shouldn't > be any different than XP running on regular PC hardware.
This would, of course, require that the Intel Mac BIOS (or what passes for one) initialize the system the same way a regular PC BIOS does, and/or that XP guarantees the floating-point hardware is set to a specific known state when a process is started, and/or that SPSS is careful to reset the state itself because it doesn't trust the BIOS or operating system. Phrased differently - there's lots of ways to screw up setting things like rounding modes and the like. Favorite bug I've seen - when I was still at my previous university, one of the professors had a huge numerical simulation that he would test-run on our IBM 4341, and then run on the big 3090-600J's down at the Cornell Theory Center. (Particularly ugly math - it was basically solving a multiple integral of a multiply-discontinuous function, between endpoints which were *themselves* the values of integrals of discontinuous functions). He ran into one test case that would crash if run during the day, but would run just fine if run overnight. After a *LOT* of time on his part, and the Theory Center's part, and IBM engineers part, they found it: When run at night, his code would get onto the vector processors in the 3090 and get *lots* of iterations done between the relatively infrequent I/O interrupts that would happen at night, so he was *effectively* getting about 132 bits of precision (128 for the official plus 4 for a guard digit in the hardware). However, during the day, interrupts happened a lot more because people were logged on and editing and compiling and the like, and when the operating system did save/restore of the vector registers, they only saved 128 bits. And the function was numerically unstable enough that it needed 130 or so bits....
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