source: buchla-68k/orig/DATE/UTIME.C@ 6888aa2

/*
   =============================================================================
        time.c -- translate GEMDOS time format to Unix internal time format
        Version 2 -- 1989-01-10 -- D.N. Lynx Crowe

        Unix(tm) keeps its time in seconds since 1970-01-01 00:00:00 GMT.
   =============================================================================
*/

#define TIMEZONE        8               /* PST */

#include "osbind.h"
#include "stddefs.h"

static char mdays[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

static
int
days(y)
register int y;
{
        if (y < 1970)
                y += 1900;

        if (((y % 4) EQ 0) AND ((y % 100) OR ((y % 400) EQ 0)))
                y = 366;
        else
                y = 365;

        return(y);
}

long
time(tloc)
long *tloc;
{
        long _time;
        int i, j, year, month, day, hour, minute, second, t;

        t = Gettime();

        year   = ((short)(t >> 25) & 0x007F) + 1980;
        month  =  (short)(t >> 21) & 0x000F;
        day    =  (short)(t >> 16) & 0x001F;

        hour   =  (short)(t >> 11) & 0x001F;
        minute =  (short)(t >>  5) & 0x003F;
        second =  ((short)t & 0x001F) << 1;

        _time = 0L;

        for (i = 1970, j = year; i < j; i++)
                _time += days(i) ;

        for(i = 1; i < month; i++)
                _time += mdays[i - 1] ;

        if((days(year) EQ 366) AND (month > 2))
                ++_time ;

        _time += (day - 1);
        _time *= 24;
        _time += hour + TIMEZONE;
        _time *= 60;
        _time += minute;
        _time *= 60;
        _time += second;

        if (tloc)
                *tloc = _time;

        return(_time);
}