eu_dst.h

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/*
 * (c)2012 Michael Duane Rice All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer. 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. Neither the name of the copyright holders
 * nor the names of contributors may be used to endorse or promote products
 * derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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.
 */

#ifndef EU_DST_H
#define EU_DST_H

#include "time.h"

int eu_dst(const time_t* timer, int32_t* z)
{
  struct tm tmptr;
  uint8_t month, mday, hour, day_of_week, d;
  int n;

  // Obtain the variables
  gmtime_r(timer, &tmptr);
  month = tmptr.tm_mon;
  day_of_week = tmptr.tm_wday;
  mday = tmptr.tm_mday - 1;
  hour = tmptr.tm_hour;

  if ((month > MARCH) && (month < OCTOBER))
    return ONE_HOUR;

  if (month < MARCH)
    return 0;

  if (month > OCTOBER)
    return 0;

  // Determine mday of last Sunday
  n = tmptr.tm_mday - 1;
  n -= day_of_week;
  n += 7;
  d = n % 7;
  n = 31 - d;
  n /= 7;
  d = d + 7 * n;
  if (month == MARCH) {
    if (d < mday)
      return 0;
    if (d > mday)
      return ONE_HOUR;
    if (hour < 1)
      return 0;
    return ONE_HOUR;
  }
  if (d < mday)
    return ONE_HOUR;
  if (d > mday)
    return 0;
  if (hour < 1)
    return ONE_HOUR;
  return 0;
}
#endif