faraphel/chrony
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

smooth: fix selection of 1st stage direction

Browse source 
When the smoothing process is updated with extremely small (e.g.
sub-nanosecond) values, both directions may give a negative length of
the 1st or 3rd stage due to numerical errors and the selection will fail
an in assertion. Rework the code to select the direction which gives a
smaller error.
This commit is contained in:
Miroslav Lichvar 2016-09-12 12:23:09 +02:00
parent 1d9d19d76b
commit 37d1467368
1 changed files with 31 additions and 12 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

43
smooth.c
View file

@ -137,7 +137,7 @@ get_smoothing(struct timeval *now, double *poffset, double *pfreq,
static void static void
update_stages(void) update_stages(void)
{ {
double s1, s2, s, l1, l2, l3, lc, f, f2; double s1, s2, s, l1, l2, l3, lc, f, f2, l1t[2], l3t[2], err[2];
int i, dir; int i, dir;
/* Prepare the three stages so that the integral of the frequency offset /* Prepare the three stages so that the integral of the frequency offset
@ -146,22 +146,41 @@ update_stages(void)
s1 = smooth_offset / max_wander; s1 = smooth_offset / max_wander;
s2 = smooth_freq * smooth_freq / (2.0 * max_wander * max_wander); s2 = smooth_freq * smooth_freq / (2.0 * max_wander * max_wander);
l1 = l2 = l3 = 0.0;
/* Calculate the lengths of the 1st and 3rd stage assuming there is no /* Calculate the lengths of the 1st and 3rd stage assuming there is no
frequency limit. If length of the 1st stage comes out negative, switch frequency limit. The direction of the 1st stage is selected so that
its direction. */ the lengths will not be negative. With extremely small offsets both
for (dir = -1; dir <= 1; dir += 2) { directions may give a negative length due to numerical errors, so select
the one which gives a smaller error. */
for (i = 0, dir = -1; i <= 1; i++, dir += 2) {
err[i] = 0.0;
s = dir * s1 + s2; s = dir * s1 + s2;
if (s >= 0.0) {
l3 = sqrt(s); if (s < 0.0) {
l1 = l3 - dir * smooth_freq / max_wander; err[i] += -s;
if (l1 >= 0.0) s = 0.0;
break; }
l3t[i] = sqrt(s);
l1t[i] = l3t[i] - dir * smooth_freq / max_wander;
if (l1t[i] < 0.0) {
err[i] += l1t[i] * l1t[i];
l1t[i] = 0.0;
} }
} }
assert(dir <= 1 && l1 >= 0.0 && l3 >= 0.0); if (err[0] < err[1]) {
l1 = l1t[0];
l3 = l3t[0];
dir = -1;
} else {
l1 = l1t[1];
l3 = l3t[1];
dir = 1;
}
l2 = 0.0;
/* If the limit was reached, shorten 1st+3rd stages and set a 2nd stage */ /* If the limit was reached, shorten 1st+3rd stages and set a 2nd stage */
f = dir * smooth_freq + l1 * max_wander - max_freq; f = dir * smooth_freq + l1 * max_wander - max_freq;