[Openmcl-devel] Floating point performance

Ron Garret ron at flownet.com
Sat Jan 30 23:04:52 UTC 2010


On Jan 30, 2010, at 2:43 PM, Paul Onions wrote:

> 
> 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...

You could just compile a sqrt function with gcc and call it through the FFI.

rg




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