amd64/109584: zdump doesn't work

[Vasil Dimov]

The following reply was made to PR amd64/109584; it has been noted by GNATS.

From: Vasil Dimov <vd at FreeBSD.org>
To: John Baldwin <jhb at freebsd.org>
Cc: freebsd-amd64 at freebsd.org, Daniel Crandall <dcrandall at simplestar.com>, wollman at freebsd.org, kensmith at freebsd.org, rwatson at freebsd.org, bug-followup at FreeBSD.org
Subject: Re: amd64/109584: zdump doesn't work
Date: Wed, 28 Feb 2007 08:43:37 +0200

 On Tue, Feb 27, 2007 at 14:54:14 -0500, John Baldwin wrote:
 [...]
 > zdump works by trying to enumerate all the possible 
 > values of time_t.  On a 32-bit machine this means going from -2^31 to
 > 2^31 - 1.  On amd64 which has a 64-bit time_t, this means from from -2^63 to 
 > 2^63 - 1.
 
 Yes, this is true.
 
 > If you understand exponential math you will see that the zone files aren't 
 > corrupted, and zdump isn't hung.  Rather, it's just taking a long time to 
 > run.
 
 I think this is not the case. It is actually hung in infinite loop in
 localtime(3) in libc. Try the following code on amd64 platform:
 
 --- cut ---
 time_t	t;
 t = -9223372036762365600;
 localtime(&t);
 --- cut ---
 
 it hangs in this loop:
 
 src/lib/libc/stdtime/localtime.c:
 1320         y = EPOCH_YEAR;
 1321 #define LEAPS_THRU_END_OF(y)    ((y) / 4 - (y) / 100 + (y) / 400)
 1322         while (days < 0 || days >= (long) year_lengths[yleap = isleap(y)]) {
 1323                 long    newy;
 1324
 1325                 newy = y + days / DAYSPERNYEAR;
 1326                 if (days < 0)
 1327                         --newy;
 1328                 days -= (newy - y) * DAYSPERNYEAR +
 1329                         LEAPS_THRU_END_OF(newy - 1) -
 1330                         LEAPS_THRU_END_OF(y - 1);
 1331                 y = newy;
 1332         }
 
 where days oscillates between -1 and 365, y and newy between
 -292277022654 and -292277022655. E.g. try so see what happens if you
 enter the loop with days=365 and y=-292277022655.
 
 -- 
 Vasil Dimov
 gro.DSBeerF at dv
 %
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