* sqrt in kernel?
@ 2001-05-20 20:33 Robert M. Love
2001-05-20 21:33 ` Matti Aarnio
2001-05-20 21:33 ` John Levon
0 siblings, 2 replies; 4+ messages in thread
From: Robert M. Love @ 2001-05-20 20:33 UTC (permalink / raw)
To: linux-kernel
hi,
is there a sqrt function in the kernel? any other math functions?
i tried finding/grepping around, and found some various arch-specific
stuff for fpu emulation... is there a general sqrt function? is there a
single file to look through with the various math functions?
thanks,
--
Robert M. Love
rml@ufl.edu
rml@tech9.net
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: sqrt in kernel?
2001-05-20 20:33 sqrt in kernel? Robert M. Love
@ 2001-05-20 21:33 ` Matti Aarnio
2001-05-20 23:31 ` Ingo Molnar
2001-05-20 21:33 ` John Levon
1 sibling, 1 reply; 4+ messages in thread
From: Matti Aarnio @ 2001-05-20 21:33 UTC (permalink / raw)
To: Robert M. Love; +Cc: linux-kernel
On Sun, May 20, 2001 at 04:33:20PM -0400, Robert M. Love wrote:
> hi,
>
> is there a sqrt function in the kernel? any other math functions?
No. (Assuming FP math sqrt function is your interest.)
If you do scaled integers (fractions, with 2^n denominator),
you can do newton iteration for sqrt nicely.
> i tried finding/grepping around, and found some various arch-specific
> stuff for fpu emulation... is there a general sqrt function? is there a
> single file to look through with the various math functions?
Yes. Userspace. ( <math.h> )
As a rule: NO FP MATH IS ALLOWED IN THE KERNEL!
Now the question: Why do you think you need FP math ?
If your case is non-fast-path, you may do complete
state save before, and restore after your FP code.
In some cases even the fast-paths carry FP/MMX code,
but those are cases where the save/restore overhead
becomes negligible for all of the other processing
that is going on.
> thanks,
> --
> Robert M. Love
> rml@ufl.edu
> rml@tech9.net
/Matti Aarnio
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: sqrt in kernel?
2001-05-20 21:33 ` Matti Aarnio
@ 2001-05-20 23:31 ` Ingo Molnar
0 siblings, 0 replies; 4+ messages in thread
From: Ingo Molnar @ 2001-05-20 23:31 UTC (permalink / raw)
To: Matti Aarnio; +Cc: Robert M. Love, linux-kernel
On Mon, 21 May 2001, Matti Aarnio wrote:
> In some cases even the fast-paths carry FP/MMX code,
> but those are cases where the save/restore overhead
> becomes negligible for all of the other processing
> that is going on.
even in that case you must make sure you dont raise any FP exceptions,
which could change the non-CPU based FPU context of the process.
Ingo
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: sqrt in kernel?
2001-05-20 20:33 sqrt in kernel? Robert M. Love
2001-05-20 21:33 ` Matti Aarnio
@ 2001-05-20 21:33 ` John Levon
1 sibling, 0 replies; 4+ messages in thread
From: John Levon @ 2001-05-20 21:33 UTC (permalink / raw)
To: Robert M. Love; +Cc: linux-kernel
On 20 May 2001, Robert M. Love wrote:
> hi,
>
> is there a sqrt function in the kernel?
no. read the FAQ.
> i tried finding/grepping around, and found some various arch-specific
> stuff for fpu emulation... is there a general sqrt function? is there a
In general questions like this are better asked on the kernelnewbies list. Read
the FAQ.
john
^ permalink raw reply [flat|nested] 4+ messages in thread
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2001-05-20 20:33 sqrt in kernel? Robert M. Love
2001-05-20 21:33 ` Matti Aarnio
2001-05-20 23:31 ` Ingo Molnar
2001-05-20 21:33 ` John Levon
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