Re: Time precision

[Pablo Molinero Fernandez <molinero@stanford.edu>]

Hi Massimo,

I agree with you. I think that in the next ns release they should maintain
the precission of the traces throughout the simulation. It is a simple
matter of changing lines 255 and 276 in ns-2/ns-2/trace.cc from:

sprintf(wrk_, "%c %g %d %d %s %d %s %d %s%s %s%s %d %d",

to:

sprintf(wrk_, "%c %.9g %d %d %s %d %s %d %s%s %s%s %d %d",

or:

sprintf(wrk_, "%c %.9f %d %d %s %d %s %d %s%s %s%s %d %d",

Pablo

On Tue, 15 Jun 1999, Massimo Pegorer - Stage wrote:

> Running some simulations I've noticed that time in ns output files is
> always given with the six most significant digits, and this fact gives
> me some problems in postprocessing these files because of the rounding;
> for example, when the time goes beyond 100 seconds, fractions of msec
> are lost:
> 
> [...]
> - 99.9961 0 1 cbr 1000 ------- 0 0.0 1.0 19803 19803
> r 99.9962 0 1 cbr 1000 ------- 0 0.0 1.0 19801 19801
> r 100.001 0 1 cbr 1000 ------- 0 0.0 1.0 19802 19802
> + 100.003 0 1 cbr 1000 ------- 0 0.0 1.0 19804 19804
> [...]
> 
> This has curious consequences for nam, too. For absurde, if you have a
> cbr flow with 5ms interval time between packets (interval_=0.005) and it
> starts at 1000, packets #0 and #1 will have the same start-time (1000)
> and nam will visualize only packet #1 and not #0!
> 
> + 1000 0 1 cbr 1000 ------- 0 0.0 1.0 0 0
> - 1000 0 1 cbr 1000 ------- 0 0.0 1.0 0 0
> + 1000 0 1 cbr 1000 ------- 0 0.0 1.0 1 1
> - 1000 0 1 cbr 1000 ------- 0 0.0 1.0 1 1
> + 1000.01 0 1 cbr 1000 ------- 0 0.0 1.0 2 2
> - 1000.01 0 1 cbr 1000 ------- 0 0.0 1.0 2 2
> r 1000.01 0 1 cbr 1000 ------- 0 0.0 1.0 0 0
> + 1000.01 0 1 cbr 1000 ------- 0 0.0 1.0 3 3
> - 1000.01 0 1 cbr 1000 ------- 0 0.0 1.0 3 3
> r 1000.01 0 1 cbr 1000 ------- 0 0.0 1.0 1 1
> r 1000.02 0 1 cbr 1000 ------- 0 0.0 1.0 2 2
> [...]
> 
> I think this depends on sprintf %g default precisions (in
> Trace::format), but in my opinion it would be more useful to have always
> time with the same format and with six digits after the decimal-point
> (microsec), such as with %f.
> I hope not to have annoyed you with tedious questions. Thanks for
> suggest.
> 
> max
> 
> 
> --
> Massimo Pegorer, student
> Dipartimento di Elettronica e Informatica
> Universita' degli Studi di Padova
> Padova - ITALIA
> 
> 

-------------------------------------------------
Pablo Molinero Fern�ndez
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