[ntp:questions] Popcorn on prefer takes out system clock

Dave Hart davehart at gmail.com
Wed Mar 7 04:34:32 UTC 2012

On Wed, Mar 7, 2012 at 01:32, <Null at blacklist.anitech-systems.invalid> wrote:
> Dave Hart wrote:
>> A C <agcarver+ntp at acarver.net> wrote:
>>> 944d 8d popcorn 2147483647.997598 s
>> I assume you mean in the local ntpd log on your sparc box
>>  referring to the IP address that used to be marked prefer.
>> I realize not everyone is a programmer, but the number
>>  above jumped out at me as suspiciously round in hex
>>  and binary.  Sure enough, round it to whole seconds
>>  and you have 2^31 or 0x80000000.  Incredible coincidence?
> -0.002402 ?

Nope.  NTP's 32:32 l_fp is used for both unsigned timestamps and
signed differences between timestamps (intervals or offsets).  In both
cases the fractional part is unsigned and positive.  For offsets, the
integer part is signed, so -0.002402 would be -1 seconds plus
0.997598, or in hex 0xffffffff.0xf.......  In this case we have an
unambiguously positive value 0x7fffffff.0xf....... or just over +68

Dave Hart

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