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    SubjectRe: [RFC][PATCH 1/4] add jiffies_to_nsecs() helper and fix up size of usecs
    On 15.07.2005 [14:14:25 +0200], Pavel Machek wrote:
    > Hi!
    >
    > > > > +static inline u64 jiffies_to_nsecs(const unsigned long j)
    > > > > +{
    > > > > +#if HZ <= NSEC_PER_SEC && !(NSEC_PER_SEC % HZ)
    > > > > + return (NSEC_PER_SEC / HZ) * (u64)j;
    > > > > +#elif HZ > NSEC_PER_SEC && !(HZ % NSEC_PER_SEC)
    > > > > + return ((u64)j + (HZ / NSEC_PER_SEC) - 1)/(HZ / NSEC_PER_SEC);
    > > > > +#else
    > > > > + return ((u64)j * NSEC_PER_SEC) / HZ;
    > > > > +#endif
    > > > > +}
    > > >
    > > > That might look a little better something like:
    > > >
    > > > static inline u64 jiffies_to_nsecs(const unsigned long __j)
    > > > {
    > > > u64 j = __j;
    > > >
    > > > if (HZ <= NSEC_PER_SEC && !(NSEC_PER_SEC % HZ))
    > > > return (NSEC_PER_SEC / HZ) * j;
    > > > else if (HZ > NSEC_PER_SEC && !(HZ % NSEC_PER_SEC))
    > > > return (j + (HZ / NSEC_PER_SEC) - 1)/(HZ / NSEC_PER_SEC);
    > > > else
    > > > return (j * NSEC_PER_SEC) / HZ;
    > > > }
    > > >
    > > > Compilers are smart :)
    > >
    > > Well, I was trying to keep it similar to the other conversion functions.
    > > I guess the compiler can evaluate the conditional full of constants at
    > > compile-time regardless of whether it is #if or if ().
    > >
    > > I can make these changes if others would like them as well.
    >
    > Yes, please. And feel free to convert nearby functions, too ;-).

    I have a patch to make this change for all the jiffies <--> human-time
    functions, but have a problem. I noticed that these functions, in the
    if/else form (as opposed to #if/#else) will warn about division-by-zero
    problems, as (HZ / MSEC_PER_SEC), (HZ / USEC_PER_SEC) & (HZ /
    NSEC_PER_SEC) are all 0 if HZ < 1000 (which, of course, is the default
    now :) ). Any suggestions? Just leave the functions as is? Even then,
    I'm going to update this patch to use USEC_PER_SEC and MSEC_PER_SEC in
    the other conversion functions like I use NSEC_PER_SEC in the first
    version.

    Thanks,
    Nish
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