hi Dave:
Thanks for your kind reply.
2011/5/20 Dave Hylands [off-list ref]:

Hi lody,

On Thu, May 19, 2011 at 8:34 PM, loody [off-list ref] wrote:

quoted

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.

why the name "__udivdi3" has relation to 64-bits arighmetic?
Why linker ask for "__udivdi3", it seems there is a common sense for
linker that when doing 64-bits calculation it will try to find
"__udivdi3", am i right?

quoted

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.

the 64-bit division seem supported in gcc toolchain, and gcc will take
care the platform issue when we cross-compile the gcc, right?
It should be safe to static link the 64bits division in gcc.

-- 
Regards,