From: dhylands@gmail.com (Dave Hylands)
To: kernelnewbies@lists.kernelnewbies.org
Subject: about 64-bits division in kernel
Date: Thu, 19 May 2011 21:15:07 -0700 [thread overview]
Message-ID: <BANLkTinjDOR57PydHKxpHbcG6umgjJEifQ@mail.gmail.com> (raw)
In-Reply-To: <BANLkTimGGQgmg+nULVLAUPJ3Z3qj6pgSbg@mail.gmail.com>
Hi lody,
On Thu, May 19, 2011 at 8:34 PM, loody <miloody@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
next prev parent reply other threads:[~2011-05-20 4:15 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-20 3:34 about 64-bits division in kernel loody
2011-05-20 4:15 ` Dave Hylands [this message]
2011-05-20 5:51 ` loody
2011-05-20 6:47 ` Dave Hylands
2011-05-21 6:57 ` loody
2011-05-21 7:22 ` Dave Hylands
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