Re: [PATCH] Consolidate multiple implementations of jiffies-msecs conversions.

Sridhar Samudrala wrote:

On Fri, 26 Mar 2004, Edgar Toernig wrote:

quoted

Sridhar Samudrala wrote:

quoted

[...]
-#define MSECS(ms)  (((ms)*HZ/1000)+1)
-return (((ms)*HZ+999)/1000);
+return (msecs / 1000) * HZ + (msecs % 1000) * HZ / 1000;

Did you check that all users of the new version will work correctly
with your rounding?  Explicit round-up of delays is often required,
especially when talking to hardware...

[...] 
I guess you are referring to cases when HZ < 1000(ex: 100) and msecs is
less than 10. In those cases, the new version returns 0, whereas some of the
older versions return 1.

Exactly - but not only <10.  Any value that is not exactly representable
in jiffies.  I.e. for a delay of 15ms one has to wait 2 jiffies on a 100HZ
system.  Your version would give 1 jiffy = 10ms -- too short.

Ciao, ET.