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Replace the way we calculate the standard deviation with the unbiased form 

for non-related samples. There are several websites that explain why we
should use this form instead of the normal formula to compute the std. dev.
(Wikipedia is one of them).
Also, ping(8) (where this "new" formula came from) already does it this way
so, I'm trying to score some extra points by making both utilities behave
the same way.

Thanks to wrtstuden@ for the initial clarification.
This commit is contained in:
rpaulo 2006-05-18 02:14:22 +00:00
parent 758cf626b4
commit 25ff2bc882
1 changed files with 3 additions and 3 deletions
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6
sbin/ping6/ping6.c
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@ -1,4 +1,4 @@
/* $NetBSD: ping6.c,v 1.68 2006/05/07 16:00:18 rpaulo Exp $ */ /* $NetBSD: ping6.c,v 1.69 2006/05/18 02:14:22 rpaulo Exp $ */
/* $KAME: ping6.c,v 1.164 2002/11/16 14:05:37 itojun Exp $ */ /* $KAME: ping6.c,v 1.164 2002/11/16 14:05:37 itojun Exp $ */
/* /*
@ -77,7 +77,7 @@ static char sccsid[] = "@(#)ping.c 8.1 (Berkeley) 6/5/93";
#else #else
#include <sys/cdefs.h> #include <sys/cdefs.h>
#ifndef lint #ifndef lint
__RCSID("$NetBSD: ping6.c,v 1.68 2006/05/07 16:00:18 rpaulo Exp $"); __RCSID("$NetBSD: ping6.c,v 1.69 2006/05/18 02:14:22 rpaulo Exp $");
#endif #endif
#endif #endif
@ -2109,7 +2109,7 @@ summary(void)
/* Only display average to microseconds */ /* Only display average to microseconds */
double num = nreceived + nrepeats; double num = nreceived + nrepeats;
double avg = tsum / num; double avg = tsum / num;
double dev = sqrt(tsumsq / num - avg * avg); double dev = sqrt((tsumsq - num * avg * avg) / (num - 1));
(void)printf( (void)printf(
"round-trip min/avg/max/std-dev = %.3f/%.3f/%.3f/%.3f ms\n", "round-trip min/avg/max/std-dev = %.3f/%.3f/%.3f/%.3f ms\n",
tmin, avg, tmax, dev); tmin, avg, tmax, dev);