Re: How to use floating point in *initializations*, then cast to int or long

[Jim Cromie <jim.cromie@xxxxxxxxx>]

Jon Masters wrote:
> On 4/27/06, Ming Zhang <mingz@xxxxxxxxxxx> wrote:
>
> > kernel does not allow float point computation. google about why.
>
> However, if the original poster just wanted higher precision on 32-bit
> then there is limited support in-kernel for 64-bit arthimetic.
> Functions like do_div can help, if you're stuck.
>
> Jon.
>
> --

Related question -

In-kernel code must do shift then int-multiply to get approximation of 
floating point mult.
Is it possible use floating point math at compile-time (ie reduced by 
gcc to constants)
to compute the shift and multiply terms ?

In a sense, it could be done by macros which extract the mantissa & 
exponent from a
floating point number ( except that this implies the availability of 
that floating-point register)

The use-case Im thinking of is the new Generic-Timekeeping-System code 
now in 17-rcX-mmY
(X >=1) iirc.  Computing the .shift, .mult values at compile-time in 
macros that hide
the complexities would be nice.  There are runtime helper-funcs that use 
do_div().

-jimc



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