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ntpd: add a comment, no code changes

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Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2010-01-01 21:59:49 +01:00
parent 61313117a0
commit e4844b8a5f
1 changed files with 8 additions and 1 deletions
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9
networking/ntpd.c
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@ -432,7 +432,7 @@ filter_datapoints(peer_t *p, double t)
sum += dispersion(&p->filter_datapoint[idx], t) / (2 << i);
if (minoff == p->filter_datapoint[idx].d_offset) {
minoff -= 1;
minoff -= 1; /* so that we don't match it ever again */
} else
if (maxoff == p->filter_datapoint[idx].d_offset) {
maxoff += 1;
@ -447,6 +447,13 @@ filter_datapoints(peer_t *p, double t)
wavg += x; /* add another older6/64 to form older6/32 */
p->filter_offset = wavg;
p->filter_dispersion = sum;
//TODO: fix systematic underestimation with large poll intervals.
// Imagine that we still have a bit of uncorrected drift,
// and poll interval is big. Offsets form a progression:
// 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7, 0.7 is most recent.
// The algorithm above drops 0.0 and 0.7 as outliers,
// and then we have this estimation, ~25% off from 0.7:
// 0.1/32 + 0.2/32 + 0.3/16 + 0.4/8 + 0.5/4 + 0.6/2 = 0.503125
// +----- -----+ ^ 1/2
// | n-1 |