is_leap_year.cpp

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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
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 */

#include <stdlib.h>

unsigned char
is_leap_year(int year)
{
  div_t d;

  // Year must be divisible by 4 to be a leap year
  if (year & 3) return 0;

  // If theres a remainder after division by 100, year is not
  // divisible by 100 or 400
  d = div(year, 100);
  if (d.rem) return 1;

  // If the quotient is divisible by 4, then year is divisible by 400
  return ((d.quot & 3) == 0);
}