On January 28, 2002 12:10 pm, Arjan van de Ven wrote:
> Daniel Phillips wrote:
> >
> > On January 25, 2002 05:56 pm, Richard B. Johnson wrote:
> > > On Fri, 25 Jan 2002, wrote:
> > >
> > > > I am writing a module and would like to perform arithmetic on long
> > > > long variables. When I try to do this the module does not load due
> > > > to the unresolved symbols __udivdi3 and __umoddi3. I notice these
> > > > are normally defined in libc. Is there any way I can do this in a
> > > > kernel module.
> > > >
> > > > Many Thanks
> > > >
> > > > Simon.
> > >
> > > Normally, in modules, the granularity is such that divisions can
> > > be made by powers-of-two. In a 32-bit world, the modulus that you
> > > obtain with umoddi3 (the remainder from a long-long, division) should
> > > normally fit within a 32-bit variable. If you insist upon doing 64-bit
> > > math in a 32-bit world, then you can either make your own procedures
> > > and link them, of you can "appropriate" them from the 'C' runtime
> > > library code, include them with your source, assemble, and link them
> > > in.
> >
> > Let's be clear on one thing. There is nothing unnatural about
> > 32bits * 32bits = 64bits or 64bits / 32bits = 32bits in a 32 bit world.
> > In fact, it is a rare architecture that does not support this directly
> > in hardware. It may be awkward to express it in C, but since when has
> > that ever stopped us from using the best machine instructions for the
> > job?
> >
> > Personally, I find the omission of these mixed size muldiv operations
> > from the kernel a great inconvenience.
>
> *cough* #include <asm/div64.h> *cough*
Thanks, it's a start, but it is half of what's needed at best. A 32*32=64
mul is needed as well. Also, the div you allude to is expressed in an
awkward form. It's better than nothing, but it's far from as useful as it
could be.
I have a reasonably useful pair of operations constructed some time back,
which I'll offer if the thread doesn't heat up too much.
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