Package: iputils-ping Version: 3:20180629-2 Usually, ping reports times like 17.1 ms, but every once in a while it reports a trip time of, say, 17.10 ms. I expect to always get 3 significant digits, not sometimes 4. Here is a transcript:
$ ping 1.1.1.1
(...)
64 bytes from 1.1.1.1: icmp_seq=5318 ttl=53 time=16.4 ms
64 bytes from 1.1.1.1: icmp_seq=5319 ttl=53 time=17.1 ms
64 bytes from 1.1.1.1: icmp_seq=5320 ttl=53 time=13.8 ms
64 bytes from 1.1.1.1: icmp_seq=5321 ttl=53 time=17.10 ms
64 bytes from 1.1.1.1: icmp_seq=5322 ttl=53 time=13.9 ms
(...)
I traced this back to function gather_statistics in file ping_common.c.
The current rounding is in these lines:
$ grep -n 'triptime >= 10000)' -B 3 -A 9 ping_common.c
855- if (timing) {
856- if (triptime >= 100000)
857- printf(" time=%ld ms", (triptime+500)/1000);
858: else if (triptime >= 10000)
859- printf(" time=%ld.%01ld ms", triptime/1000,
860- ((triptime%1000)+50)/100);
861- else if (triptime >= 1000)
862- printf(" time=%ld.%02ld ms", triptime/1000,
863- ((triptime%1000)+5)/10);
864- else
865- printf(" time=%ld.%03ld ms", triptime/1000,
866- triptime%1000);
867- }
The bug happens for example with triptime = 17981:
triptime/1000 = 17981/1000
= 17 (seconds)
(triptime%1000)+50)/100 = (17981%1000)+50)/100
= ( 981 +50)/100
= 1031 /100
= 10 (tenths of a second)
So, while 17981 ms should have been converted to 18.0 seconds, it is
converted to 17.10 seconds.
One way of fixing it:
if (timing) {
if (triptime >= 100000 - 50)
printf(" time=%ld ms", (triptime+500)/1000);
else if (triptime >= 10000 - 5)
printf(" time=%ld.%01ld ms", (triptime+50)/1000,
((triptime+50)%1000)/100);
else if (triptime >= 1000)
printf(" time=%ld.%02ld ms", (triptime+5)/1000,
((triptime+5)%1000)/10);
else
printf(" time=%ld.%03ld ms", triptime/1000,
triptime%1000);
}
I fixed the triptime thresholds so the output is consistent, added the
+50/+5 to the whole milliseconds so it gets rounded as well, and moved
the +50/+5 of the fractional milliseconds to the correct place.
The code is far less readable, so may I suggest that you consider
rewriting the code so it is better maintainable than my suggested fix?
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