zdump on amd64

[Andriy Gapon]

on 19/03/2007 16:15 Andriy Gapon said the following:
> Strange problem:
> $ uname -srm
> FreeBSD 6.2-RELEASE-p2 amd64
> 
> $ zdump -v EST
> EST  Sun Jan 26 08:29:52 -219 UTC = Sun Jan 26 03:29:52 -219 EST isdst=0
> gmtoff=-18000
> EST  Mon Jan 27 08:29:52 -219 UTC = Mon Jan 27 03:29:52 -219 EST isdst=0
> gmtoff=-18000
> EST  Fri Jan  1 04:59:59 -219 UTC = Thu Dec 30 23:59:59 -219 EST isdst=0
> gmtoff=-18000
> EST  Fri Jan  1 05:00:00 -219 UTC = Fri Jan  1 00:00:00 -219 EST isdst=0
> gmtoff=-18000
> ^C
...
> Before each ^C zdump was hanging eating 100% CPU.
> Something about 64-bitness ?

Hmm. I hurried to assert that it was hanging, it was actually searching.
It seems that zdump -v algorithm is to start with minimal time_t
possible (large negative number in our case) and to go to maximum time_t
using 12 hours increments and doing certain checks for DST jumps.
Well, with 64-bit time_t start date is somewhere 200 milliard (10^9)
years ago and end date is the same in the future, so iteration over
those years takes quite a while. And tz db doesn't contain anything
useful for too distant years anyway.

I think that zdump should be optimized to limit its search range. At the
very least for the start point - what is current estimate of the age of
our Universe :-)


-- 
Andriy Gapon