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Message-ID: <CAH2r5mvCAatcvpUKdyexqeHjRCQ8niFpO6ovZsh6xiMU=rXwvg@mail.gmail.com>
Date: Thu, 11 Sep 2014 03:03:45 -0500
From: Steve French <smfrench@...il.com>
To: LKML <linux-kernel@...r.kernel.org>
Subject: 64 bit signed division
Does 64 bit signed division work on all archs?
Since do_div (currently used by cifs and ntfs to convert time formats
from DCE time to Linux time) does not handle negative numbers, and
there does not appear to be a kernel equivalent of Ildiv, I was
wondering if there really is a problem with simply doing s64 division
on other architectures (it obviously works on my systems but they are
Intel and AMD).
ie I have to change from
- u64 t = le64_to_cpu(ntutc) - NTFS_TIME_OFFSET;
-
- ts.tv_nsec = do_div(t, 10000000) * 100;
- ts.tv_sec = t;
to something like
+ s64 t = le64_to_cpu(ntutc) - NTFS_TIME_OFFSET;
+
+ ts.tv_sec = t / 10000000;
+ ts.tv_nsec = (t % 10000000) * 100;
If 64 bit division does not work on all archs then I will need to fall
back to something uglier,
+ s64 t = le64_to_cpu(ntutc) - NTFS_TIME_OFFSET;
+
+ if (t < 0) {
+ t = -t;
+ ts.tv_nsec = -(do_div(t, 10000000) * 100);
+ ts.tv_sec = -t;
+ } else {
+ ts.tv_nsec = do_div(t, 10000000) * 100;
+ ts.tv_sec = t;
+ }
Are there better alternatives?
--
Thanks,
Steve
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