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Get the magnitude of the NTP adjustment right.

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Poul-Henning Kamp 2002-03-28 16:02:44 +00:00
parent 079f9ac4c7
commit 45609bea17
1 changed files with 4 additions and 3 deletions
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7
sys/kern/kern_tc.c
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@ -238,10 +238,11 @@ tco_setscales(struct timecounter *tc)
/*
* We get nanoseconds with 32 bit binary fraction and want
* 64 bit binary fraction: x = a * 2^32 / 10^9 = a * 4.294967296
* The range is +/- 500PPM so we can multiply by about 8500
* without overflowing. 4398/1024 = is very close to ideal.
* The range is +/- 500PPM so we can only multiply by about 8500
* without overflowing. The best suitable fraction is 4398/1024.
* Divide by 2 times 1024 to match the temporary lower precision.
*/
scale += (tc->tc_adjustment * 4398) >> 10;
scale += (tc->tc_adjustment * 4398) / 2048;
scale /= tc->tc_tweak->tc_frequency;
tc->tc_scale = scale * 2;
}