dostime.c

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/*
  dostime.c - routines for converting UNIX time to MS-DOS time and vice versa.

  Various Copyrights:

  First written by Mark Adler, Richard B. Wales, Jean-loup Gailly,
  Kai Uwe Rommel, Onno van der Linden and Igor Mandrichenko (1990-1997).
  Tweaked further by Bryan Burns (1999).
  Redesigned with full error checks by Alexis Wilke (2015).

  This program is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License
  as published by the Free Software Foundation; either version 2
  of the License, or (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
*/

#include "dostime.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>


dostime_t mindostime()
{
    // Jan 1, 1980 00:00:00 is the minimum
    return 0x00210000;
}


dostime_t maxdostime()
{
    // Dec 31, 2107 23:59:59 is the maximum
    return 0xFF9FBF7D;
}


time_t dos2unixtime(dostime_t dostime)
{
    struct tm t;         /* argument for mktime() */

    memset(&t, 0, sizeof(t));

    t.tm_isdst = -1;     /* let mktime() determine if DST is in effect */
    /* Convert DOS time to UNIX time_t format */
    t.tm_sec  = (((int)dostime <<  1) & 0x3E);
    t.tm_min  = (((int)dostime >>  5) & 0x3F);
    t.tm_hour = (((int)dostime >> 11) & 0x1F);
    t.tm_mday = (((int)dostime >> 16) & 0x1F);
    t.tm_mon  = (((int)dostime >> 21) & 0x0F) - 1;
    t.tm_year = (((int)dostime >> 25) & 0x7F) + 80;

    if(t.tm_year < 80 || t.tm_year > 207
    || t.tm_mon  <  0 || t.tm_mon  >  11
    || t.tm_mday <  1 || t.tm_mday >  31 
    || t.tm_hour <  0 || t.tm_hour >  23
    || t.tm_min  <  0 || t.tm_min  >  59
    || t.tm_sec  <  0 || t.tm_sec  >  59)
    {
        return -1;
    }

    // A full round trip between Unix date to DOS and back to Unix works
    // as is (without worry about the current timezone) because the DOS
    // format makes use of localdate() and that's 1 to 1 compatible with
    // mktime() which expects a local date too.
    return mktime(&t);
}


/* \brief Convert a broken up date to a DOS date.
 *
 * Convert the date y/n/d and time h:m:s to a four byte DOS date and
 * time (date in high two bytes, time in low two bytes allowing magnitude
 * comparison).
 *
 * The function returns zero if the month, day, hour, minute, second are
 * out of range.
 *
 * \todo
 * The dostime_t type is 32 bits, although if it were 64 bits we would
 * never have an overflow with the maximum. However, the Zip archive
 * format only supports 32 bits as far as I know.
 *
 * \param[in] year  The year.
 * \param[in] month  The month.
 * \param[in] day  The day.
 * \param[in] hour  The hour.
 * \param[in] minute  The minute.
 * \param[in] second  The second.
 *
 * \return The date parameters transformed in a DOS time value or zero if the
 *         date is considered invalid.
 */
dostime_t dostime(int year, int month, int day, int hour, int minute, int second)
{
    if(year < 1980 || year > 2107
    || month < 1 || month > 12
    || day < 1 || day > 31
    || hour < 0 || hour > 23
    || minute < 0 || minute > 59
    || second < 0 || second > 59)
    {
        return 0;
    }

    return (((dostime_t) year - 1980) << 25)
         | (((dostime_t) month      ) << 21)
         | (((dostime_t) day        ) << 16)
         | (((dostime_t) hour       ) << 11)
         | (((dostime_t) minute     ) <<  5)
         | (((dostime_t) second     ) >>  1);  // 1 every other second
}


dostime_t unix2dostime(time_t unix_time)
{
    time_t even_time;
    struct tm *s;         /* result of localtime() */

    even_time = (unix_time + 1) & ~1;         /* Round up to even seconds. */
    s = localtime(&even_time);         /* Use local time since MSDOS does. */
    return dostime(s->tm_year + 1900, s->tm_mon + 1, s->tm_mday,
                   s->tm_hour, s->tm_min, s->tm_sec);
}


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