Re: using doubles in the kernel

[Joseph A Knapka <jknapka@earthlink.net>]

Lars Olsson wrote:
> 
> Dear all,
> Is there any reason why you should not use doubles and floats in the
> kernel? I remember that someome said that you should not use floating
> point types but I can't remember where. I need to use floating point
> number since I'm implementing a neural network (executing in kernel
> space because of performance reasons) and it is alot easier to implement
> this with floating point numbers.

I believe you are out of luck. As I understand it, the kernel
may not use the FPU because to do so would interfere with
user-space processes' use of the FPU. According to the
kernel-hacking HOWTO:

"
No floating point or MMX

     The FPU context is not saved; you would mess with some user 
     process' FPU. If you really want to do this, you would have
     to explicitely save/restore the full FPU state (and avoid
     context switches). It is generally a bad idea; use fixed point
     arithmetic first. 
"

Cheers,

-- Joe
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