about 64-bits division in kernel

[Dave Hylands]

Hi lody,

On Thu, May 19, 2011 at 8:34 PM, loody <miloody at gmail.com> wrote:
> hi all:
> My platform is 32-bits cpu and I need following calculation in my driver.
> #define longdiv(sr1, sr2, div)      (unsigned long )((((unsigned long
> long)(sr1) << 32) ^ (sr2)) / (div))
>
> my question are:
> 1. why "__udivdi3" has any relationship with above calculation?

Because you're doing 64 bit arithmetic (unsigned long long) and 64 bit
division is not supported in all kernels.

> 2. I know the above calculation is implemented in clibc, but why
> kernel still implement itself?
>     why kernel try to make another wheel instead of including what
> clib provided ?

The kernel doesn't use anything from the C runtime  library at all.

64-bit division and floating point are 2 things not supported in the
kernel, although they do happen to word on some platforms, they aren't
portable operations.

-- 
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com