Ben Duncan <ben@xxxxxxxxxxxxxxxxxx> wrote:
Anybody know of how to get mktime or has a routine to return
time values BEFORE the Epoch (12/31/1969).
I have no problem with such values under Linux (debian woody, using
glibc):
slsh> tm = localtime (-100000000);
slsh> print (tm);
{tm_sec=20, tm_min=13, tm_hour=9, tm_mday=31, tm_mon=9, tm_year=66, tm_wday=1, tm_yday=303, tm_isdst=0}
slsh> mktime (tm);
-100000000
What OS are you using?
FWIW, here are some routines that I use to convert Unix time_t values
to and from Julian dates:
% This algorithm came from the calendar FAQ, and appears to have been derived
% from "A Machine Algorithm for Processing Calendar Dates"
% by Fliegel and Flandern in Communications of the ACM from 1968.
define tms_to_jd (tms)
{
variable month = tms.tm_mon + 1;
variable a = (14 - month)/12;
variable y = (1900+tms.tm_year)+4800-a;
variable m = month + 12*a - 3;
variable day = tms.tm_mday;
variable jd = day + (153*m+2)/5 + y*365 + y/4 - y/100 + y/400 - 32045;
% The julian day begins at noon
jd -= 0.5;
return jd + (tms.tm_hour + (tms.tm_min + tms.tm_sec/60.0)/60.0)/24.0;
}
define tms_to_mjd (tms)
{
return tms_to_jd (tms) - 2400000.5;
}
define unix_to_mjd (t)
{
return tms_to_mjd (gmtime (t));
}
define mjd_to_unix (mjd)
{
variable t0 = 0;
variable t1 = 0x7FFFFFFFU;
variable mjd0 = unix_to_mjd (t0);
variable mjd1 = unix_to_mjd (t1);
if ((mjd0 > mjd) or (mjd > mjd1))
verror ("%S: date cannot be represented as a unix time_t", _function_name);
forever
{
variable t = t0 + (t1-t0)/2;
variable mjd2 = unix_to_mjd (t);
if (mjd2 <= mjd)
{
if (mjd2 == mjd)
return t;
mjd0 = mjd2;
t0 = t;
continue;
}
mjd1 = mjd2;
t1 = t;
}
}
define mjd_to_year (mjd)
{
variable t = mjd_to_unix (mjd);
variable tm = gmtime (t);
variable y = 1900.0 + tm.tm_year;
variable d = tm.tm_yday + (tm.tm_hour + (tm.tm_min+tm.tm_sec/60.0)/60.0)/24.0;
y += d/365.0;
return y;
}