[Openmcl-devel] Floating point performance

Paul Onions wibble37 at mac.com
Sat Jan 30 22:43:23 UTC 2010


On 30 Jan 2010, at 22:30, Tim Bradshaw wrote:

> On 30 Jan 2010, at 22:19, Paul Onions wrote:
>
>> Okay, but if I don't have a SQRT instruction then how is CMUCL able  
>> to
>> go so fast?
>
> My uninformed guess would be that emulating the instruction entails  
> a trap at some point, while CMUCL probably does not even try to use  
> it which is much quicker.
>
> (This is based on distant experience with emulating FP on processors  
> which didn't have it, which was deeply slow.)

I think you're right. I've just downloaded the reference manual for  
the MPC7445 from Freescale (I think that's likely what I've got), and  
lo and behold in appendix B we have unimplemented instructions: fsqrt  
and fsqrts. Bugger!

So, what's the best way forward from here? I suppose I'll have to try  
coding something up myself...

Paul




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