On Thu, Mar 01, 2018 at 10:00:52PM -0600, Eric Sandeen wrote:
> On 2/28/18 9:56 PM, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@xxxxxxxxxx>
> >
> > CUrrently the 100th/sec units always report zero, such as:
> >
> > 32 MiB, 8192 ops; 0:00:21.00 (1.476 MiB/sec and 377.9260 ops/sec)
> > ^^
> >
> > This is incorrect. Fix the maths that is wrong by removing all the
> > unnecesary floating point maths and just using basic integer
> > division...
> >
> > Signed-Off-By: Dave Chinner <dchinner@xxxxxxxxxx>
> > ---
> > libxcmd/input.c | 16 ++++++++--------
> > 1 file changed, 8 insertions(+), 8 deletions(-)
> >
> > diff --git a/libxcmd/input.c b/libxcmd/input.c
> > index 441bb2fbbf34..6e7a8c9822ee 100644
> > --- a/libxcmd/input.c
> > +++ b/libxcmd/input.c
> > @@ -154,9 +154,10 @@ tdiv(double value, struct timeval tv)
> > return value / ((double)tv.tv_sec + ((double)tv.tv_usec / 1000000.0));
> > }
> >
> > -#define HOURS(sec) ((sec) / (60 * 60))
> > -#define MINUTES(sec) (((sec) % (60 * 60)) / 60)
> > -#define SECONDS(sec) ((sec) % 60)
> > +#define HOURS(sec) ((sec) / (60 * 60))
> > +#define MINUTES(sec) (((sec) % (60 * 60)) / 60)
> > +#define SECONDS(sec) ((sec) % 60)
> > +#define USEC_TO_100THS(usec) ((usec) / 1000 / 10)
>
> I guess this works but I expected to convert "microseconds to 100ths"
> via a conversion like:
>
> usec * 1sec/1000000usec * 100 hundredths/1sec
That's what the old code tried to do with floating point math and
casts, but that didn't work.
> so just for readability I'd have expected:
>
> #define USEC_TO_100THS(usec) ((usec) / 1000000 * 100)
Welcome to Integer Math 101: Integer Division. You'll always get
zero, because N / M = 0 when N < M.
> or possibly just
> #define USEC_TO_100THS(usec) ((usec) / 10000)
>
> ... I'm confused by your choice of orders of magnitude above even
> though it works - it seems a bit random to divide it that way,
> unless I'm missing something?
>
> (I had a physics teacher who drilled THINK UNITS BEFORE YOU THINK
> NUMBERS" into my head an I still do) :)
Yeah, I did. I did us->ms first, then ms->100ths. i.e.:
milliseconds = usec / 1000
hundreths = ms / 10.
This should be obvious to anyone who uses the metric system for
units of measurement. I guess I should have used "centisecs". :P
> > void
> > timestr(
> > @@ -165,14 +166,12 @@ timestr(
> > size_t size,
> > int format)
> > {
> > - double usec = (double)tv->tv_usec / 1000000.0;
> > -
> > if (format & TERSE_FIXED_TIME) {
> > if (!HOURS(tv->tv_sec)) {
> > snprintf(ts, size, "%u:%02u.%02u",
> > (unsigned int) MINUTES(tv->tv_sec),
> > (unsigned int) SECONDS(tv->tv_sec),
> > - (unsigned int) usec * 100);
> > + (unsigned int) USEC_TO_100THS(tv->tv_usec));
> > return;
> > }
> > format |= VERBOSE_FIXED_TIME; /* fallback if hours needed */
> > @@ -183,9 +182,10 @@ timestr(
> > (unsigned int) HOURS(tv->tv_sec),
> > (unsigned int) MINUTES(tv->tv_sec),
> > (unsigned int) SECONDS(tv->tv_sec),
> > - (unsigned int) usec * 100);
> > + (unsigned int) USEC_TO_100THS(tv->tv_usec));
> > } else {
> > - snprintf(ts, size, "0.%04u sec", (unsigned int) usec * 10000);
> > + snprintf(ts, size, "0.%04u sec",
> > + (unsigned int) tv->tv_usec / 100);
>
> USEC_TO_10000THS() for consistency ?
Too many bloody zeros. I'm just going to convert them all ti
milliseconds and be done with it.
-Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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