source: buchla-68k/orig/DATE/TOTIME.C

/*
   =============================================================================
        totime.c -- translate a time.h structure to Unix internal time format
        Version 2 -- 1989-01-09 -- D.N. Lynx Crowe

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

#include "stddefs.h"
#include "time.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
totime(tp, timezn) 
register struct tm *tp;         /* pointer to tm structure */
long timezn;                    /* minutes local time is offset from GMT */
{
        long ret;
        int i, j;

        ret = 0L;

        if (tp->tm_year < 70)
                return(0L);

        for (i = 1970, j = tp->tm_year + 1900; i < j; i++)
                ret += days(i) ;

        for(i = 1; i < tp->tm_mon; i++)
                ret += mdays[i - 1] ;

        if((days(tp->tm_year) EQ 366) AND (tp->tm_mon > 2))
                ++ret ;

        ret += (tp->tm_mday - 1);
        ret *= 24;
        ret += tp->tm_hour;
        ret *= 60;
        ret += (tp->tm_min + timezn);
        ret *= 60;
        ret += tp->tm_sec;

        return(ret);
}