[slang-users] TIme Routines.

[Ben Duncan]

Slackware 10.1 .....glibc

Ran your routine and got back a -1 from mktime ..

John E. Davis wrote:
> Ben Duncan <ben at versaccounting.com> 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;
> }
> 
> 

-- 
Ben Duncan   - VersAccounting Software LLC 336 Elton Road  Jackson MS, 39212
"Never attribute to malice, that which can be adequately explained by stupidity"
        - Hanlon's Razor