timegm.h

/*
 * Copyright (c) 1997 Kungliga Tekniska Högskolan
 * (Royal Institute of Technology, Stockholm, Sweden).
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * 3. Neither the name of the Institute nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <time.h>

#define ASN1_MAX_YEAR 2000

static int
is_leap(unsigned y)
{
    y += 1900;
    return (y % 4) == 0 && ((y % 100) != 0 || (y % 400) == 0);
}

static const unsigned ndays[2][12] ={
    {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
    {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}};

/*
 * This is a simplifed version of timegm(3) that doesn't accept out of
 * bound values that timegm(3) normally accepts but those are not
 * valid in asn1 encodings.
 */

time_t
_der_timegm (struct tm *tm)
{
  time_t res = 0;
  int i;

  /*
   * See comment in _der_gmtime
   */
  if (tm->tm_year > ASN1_MAX_YEAR)
      return 0;

  if (tm->tm_year < 0)
      return -1;
  if (tm->tm_mon < 0 || tm->tm_mon > 11)
      return -1;
  if (tm->tm_mday < 1 || tm->tm_mday > (int)ndays[is_leap(tm->tm_year)][tm->tm_mon])
      return -1;
  if (tm->tm_hour < 0 || tm->tm_hour > 23)
      return -1;
  if (tm->tm_min < 0 || tm->tm_min > 59)
      return -1;
  if (tm->tm_sec < 0 || tm->tm_sec > 59)
      return -1;

  for (i = 70; i < tm->tm_year; ++i)
    res += is_leap(i) ? 366 : 365;

  for (i = 0; i < tm->tm_mon; ++i)
    res += ndays[is_leap(tm->tm_year)][i];
  res += tm->tm_mday - 1;
  res *= 24;
  res += tm->tm_hour;
  res *= 60;
  res += tm->tm_min;
  res *= 60;
  res += tm->tm_sec;
  return res;
}

struct tm *
_der_gmtime(time_t t, struct tm *tm)
{
    time_t secday = t % (3600 * 24);
    time_t days = t / (3600 * 24);

    memset(tm, 0, sizeof(*tm));

    tm->tm_sec = secday % 60;
    tm->tm_min = (secday % 3600) / 60;
    tm->tm_hour = secday / 3600;

    /*
     * Refuse to calculate time ~ 2000 years into the future, this is
     * not possible for systems where time_t is a int32_t, however,
     * when time_t is a int64_t, that can happen, and this becomes a
     * denial of sevice.
     */
    if (days > (ASN1_MAX_YEAR * 365))
  return NULL;

    tm->tm_year = 70;
    while(1) {
  unsigned dayinyear = (is_leap(tm->tm_year) ? 366 : 365);
  if (days < dayinyear)
      break;
  tm->tm_year += 1;
  days -= dayinyear;
    }
    tm->tm_mon = 0;

    while (1) {
  unsigned daysinmonth = ndays[is_leap(tm->tm_year)][tm->tm_mon];
  if (days < daysinmonth)
      break;
  days -= daysinmonth;
  tm->tm_mon++;
    }
    tm->tm_mday = days + 1;

    return tm;
}