/* Helper function to handle possible wraparound of the ntp epoch.
*
* Works by periodic extension of the ntp time stamp in the UN*X epoch.
* If the 'time_t' is 32 bit, use solar cycle warping to get the value
* in a suitable range. Also uses solar cycle warping to work around
* really buggy implementations of 'gmtime()' / 'localtime()' that
* cannot work with a negative time value, that is, times before
* 1970-01-01. (MSVCRT...)
*
* Apart from that we're assuming that the localtime/gmtime library
* functions have been updated so that they work...
*
* An explanation: The julian calendar repeats ever 28 years, because
* it's the LCM of 7 and 1461, the week and leap year cycles. This is
* called a 'solar cycle'. The gregorian calendar does the same as
* long as no centennial year (divisible by 100, but not 400) goes in
* the way. So between 1901 and 2099 (inclusive) we can warp time
* stamps by 28 years to make them suitable for localtime() and
* gmtime() if we have trouble. Of course this will play hubbubb with
* the DST zone switches, so we should do it only if necessary; but as
* we NEED a proper conversion to dates via gmtime() we should try to
* cope with as many idiosyncrasies as possible.
*
*/
/*
* solar cycle in unsigned secs and years, and the cycle limits.
*/
#define SOLAR_CYCLE_SECS 0x34AADC80UL /* 7*1461*86400*/
#define SOLAR_CYCLE_YEARS 28
#define MINFOLD -3
#define MAXFOLD 3
/*
* If there is chance of truncation, try to fix it. Let the
* compiler find out if this can happen at all.
*/
while (ts != tl) { /* truncation? */
if (tl < 0) {
if (--folds < MINFOLD)
return NULL;
tl += SOLAR_CYCLE_SECS;
} else {
if (++folds > MAXFOLD)
return NULL;
tl -= SOLAR_CYCLE_SECS;
}
ts = tl; /* next try... */
}
#else
/*
* since we do not have 64-bit scalars, it's not likely we have
* 64-bit time_t. Assume 32 bits and properly reduce the value.
*/
u_int32 hi, lo;
/*
* 'ts' should be a suitable value by now. Just go ahead, but
* with care:
*
* There are some pathological implementations of 'gmtime()'
* and 'localtime()' out there. No matter if we have 32-bit or
* 64-bit 'time_t', try to fix this by solar cycle warping
* again...
*
* At least the MSDN says that the (Microsoft) Windoze
* versions of 'gmtime()' and 'localtime()' will bark on time
* stamps < 0.
*/
while ((tm = (*(local ? localtime : gmtime))(&ts)) == NULL)
if (ts < 0) {
if (--folds < MINFOLD)
return NULL;
ts += SOLAR_CYCLE_SECS;
} else if (ts >= (time_t)SOLAR_CYCLE_SECS) {
if (++folds > MAXFOLD)
return NULL;
ts -= SOLAR_CYCLE_SECS;
} else
return NULL; /* That's truly pathological! */
/* 'tm' surely not NULL here! */
INSIST(tm != NULL);
if (folds != 0) {
tm->tm_year += folds * SOLAR_CYCLE_YEARS;
if (tm->tm_year <= 0 || tm->tm_year >= 200)
return NULL; /* left warp range... can't help here! */
}
