Fallback Calculation easter_days (when calendar extension is not loaded)

src/Yasumi/Provider/ChristianHolidays.php

@@ -564,9 +564,17 @@ public function reformationDay($year, $timezone, $locale, $type = Holiday::TYPE_
  * Easter is a festival and holiday celebrating the resurrection of Jesus Christ from the dead. Easter is celebrated
  * on a date based on a certain number of days after March 21st.
  *
- * This function uses the standard PHP 'easter_days'.
+ * This function uses the standard PHP 'easter_days' function if the calendar extension is enabled. In case the
+ * calendar function is not enabled, a fallback calculation has been implemented that is based on the same
+ * 'easter_days' c function.
  *
- * @see easter_days
+ * Note: In calendrical calculations, frequently operations called integer division are used.
+ *
+ * @see easter_days
+ *
+ * @link https:/php/php-src/blob/c8aa6f3a9a3d2c114d0c5e0c9fdd0a465dbb54a5/ext/calendar/easter.c
+ * @link http://www.gmarts.org/index.php?go=415#EasterMallen
+ * @link http://www.tondering.dk/claus/cal/easter.php
  *
  * @param int $year the year for which Easter needs to be calculated
  * @param string $timezone the timezone in which Easter is celebrated
@@ -575,8 +583,55 @@ public function reformationDay($year, $timezone, $locale, $type = Holiday::TYPE_
  */
  protected function calculateEaster($year, $timezone)
  {
+ if (extension_loaded('calendar')) {
+ $easter_days = \easter_days($year);
+ } else {
+ $golden = (int)(($year % 19) + 1); // The Golden Number
+
+ // The Julian calendar applies to the original method from 326AD. The Gregorian calendar was first
+ // introduced in October 1582 in Italy. Easter algorithms using the Gregorian calendar apply to years
+ // 1583 AD to 4099 (A day adjustment is required in or shortly after 4100 AD).
+ // After 1752, most western churches have adopted the current algorithm.
+ if ($year <= 1752) {
+ $dom = ($year + (int)($year / 4) + 5) % 7; // The 'Dominical number' - finding a Sunday
+ if ($dom < 0) {
+ $dom += 7;
+ }
+
+ $pfm = (3 - (11 * $golden) - 7) % 30; // Uncorrected date of the Paschal full moon
+ if ($pfm < 0) {
+ $pfm += 30;
+ }
+ } else {
+ $dom = ($year + (int)($year / 4) - (int)($year / 100) + (int)($year / 400)) % 7; // The 'Dominical number' - finding a Sunday
+ if ($dom < 0) {
+ $dom += 7;
+ }
+
+ $solar = (int)(($year - 1600) / 100) - (int)(($year - 1600) / 400); // The solar correction
+ $lunar = (int)(((int)(($year - 1400) / 100) * 8) / 25); // The lunar correction
+
+ $pfm = (3 - (11 * $golden) + $solar - $lunar) % 30; // Uncorrected date of the Paschal full moon
+ if ($pfm < 0) {
+ $pfm += 30;
+ }
+ }
+
+ // Corrected date of the Paschal full moon, - days after 21st March
+ if (($pfm == 29) || ($pfm == 28 && $golden > 11)) {
+ --$pfm;
+ }
+
+ $tmp = (4 - $pfm - $dom) % 7;
+ if ($tmp < 0) {
+ $tmp += 7;
+ }
+
+ $easter_days = (int)($pfm + $tmp + 1); // Easter as the number of days after 21st March
+ }
+
  $easter = new DateTime("$year-3-21", new DateTimeZone($timezone));
- $easter->add(new DateInterval('P' . \easter_days($year) . 'D'));
+ $easter->add(new DateInterval('P' . $easter_days . 'D'));
 
  return $easter;
  }

tests/Australia/EasterMondayTest.php

@@ -53,8 +53,8 @@ public function HolidayDataProvider()
 
  for ($y = 0; $y < 50; $y++) {
  $year = $this->generateRandomYear();
- $date = new DateTime("$year-3-21", new DateTimeZone($this->timezone));
- $date->add(new DateInterval('P' . (easter_days($year) + 1) . 'D'));
+ $date = $this->calculateEaster($year, $this->timezone);
+ $date->add(new DateInterval('P1D'));
 
  $data[] = [$year, $date->format('Y-m-d')];
  }

tests/Australia/GoodFridayTest.php

@@ -53,8 +53,7 @@ public function HolidayDataProvider()
 
  for ($y = 0; $y < 50; $y++) {
  $year = $this->generateRandomYear();
- $date = new DateTime("$year-3-21", new DateTimeZone($this->timezone));
- $date->add(new DateInterval('P' . easter_days($year) . 'D'));
+ $date = $this->calculateEaster($year, $this->timezone);
  $date->sub(new DateInterval('P2D'));
  $data[] = [$year, $date->format('Y-m-d')];
  }

tests/Ireland/EasterMondayTest.php

@@ -53,8 +53,8 @@ public function HolidayDataProvider()
 
  for ($y = 0; $y < self::TEST_ITERATIONS; $y++) {
  $year = $this->generateRandomYear();
- $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
- $date->add(new DateInterval('P' . (easter_days($year) + 1) . 'D'));
+ $date = $this->calculateEaster($year, self::TIMEZONE);
+ $date->add(new DateInterval('P1D'));
 
  $data[] = [$year, $date->format('Y-m-d')];
  }

tests/Ireland/EasterTest.php

@@ -12,7 +12,6 @@
 
 namespace Yasumi\tests\Ireland;
 
-use DateInterval;
 use DateTime;
 use DateTimeZone;
 use Yasumi\Holiday;
@@ -53,8 +52,7 @@ public function HolidayDataProvider()
 
  for ($y = 0; $y < self::TEST_ITERATIONS; $y++) {
  $year = $this->generateRandomYear();
- $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
- $date->add(new DateInterval('P' . easter_days($year) . 'D'));
+ $date = $this->calculateEaster($year, self::TIMEZONE);
 
  $data[] = [$year, $date->format('Y-m-d')];
  }

tests/Ireland/GoodFridayTest.php

@@ -53,8 +53,7 @@ public function HolidayDataProvider()
 
  for ($y = 0; $y < self::TEST_ITERATIONS; $y++) {
  $year = $this->generateRandomYear();
- $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
- $date->add(new DateInterval('P' . easter_days($year) . 'D'));
+ $date = $this->calculateEaster($year, self::TIMEZONE);
  $date->sub(new DateInterval('P2D'));
  $data[] = [$year, $date->format('Y-m-d')];
  }

tests/Ireland/PentecostTest.php

@@ -54,8 +54,7 @@ public function HolidayDataProvider()
  //for ($y = 0; $y < self::TEST_ITERATIONS; $y++) {
  for ($y = 0; $y < 2; $y++) {
  $year = $this->generateRandomYear();
- $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
- $date->add(new DateInterval('P' . \easter_days($year) . 'D'));
+ $date = $this->calculateEaster($year, self::TIMEZONE);
  $date->add(new DateInterval('P49D'));
  $data[] = [$year, $date->format('Y-m-d')];
  }

tests/Ireland/pentecostMondayTest.php

@@ -58,8 +58,7 @@ public function HolidayDataProvider()
 
  for ($y = 0; $y < self::TEST_ITERATIONS; $y++) {
  $year = $this->generateRandomYear(1000, self::ABOLISHMENT_YEAR);
- $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
- $date->add(new DateInterval('P' . \easter_days($year) . 'D'));
+ $date = $this->calculateEaster($year, self::TIMEZONE);
  $date->add(new DateInterval('P50D'));
  $data[] = [$year, $date->format('Y-m-d')];
  }

tests/NewZealand/EasterMondayTest.php

@@ -53,8 +53,8 @@ public function HolidayDataProvider()
 
  for ($y = 0; $y < 50; $y++) {
  $year = $this->generateRandomYear();
- $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
- $date->add(new DateInterval('P' . (easter_days($year) + 1) . 'D'));
+ $date = $this->calculateEaster($year, self::TIMEZONE);
+ $date->add(new DateInterval('P1D'));
 
  $data[] = [$year, $date->format('Y-m-d')];
  }

tests/NewZealand/GoodFridayTest.php

@@ -53,8 +53,7 @@ public function HolidayDataProvider()
 
  for ($y = 0; $y < 50; $y++) {
  $year = $this->generateRandomYear();
- $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
- $date->add(new DateInterval('P' . easter_days($year) . 'D'));
+ $date = $this->calculateEaster($year, self::TIMEZONE);
  $date->sub(new DateInterval('P2D'));
  $data[] = [$year, $date->format('Y-m-d')];
  }

tests/SouthAfrica/FamilyDayTest.php

@@ -62,8 +62,7 @@ public function HolidayDataProvider()
 
  for ($y = 0; $y < 50; $y++) {
  $year = $this->generateRandomYear(self::ESTABLISHMENT_YEAR);
- $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
- $date->add(new DateInterval('P' . easter_days($year) . 'D'));
+ $date = $this->calculateEaster($year, self::TIMEZONE);
  $date->add(new DateInterval('P1D'));
  $data[] = [$year, $date->format('Y-m-d')];
  }

tests/SouthAfrica/GoodFridayTest.php

@@ -62,8 +62,7 @@ public function HolidayDataProvider()
 
  for ($y = 0; $y < 50; $y++) {
  $year = $this->generateRandomYear(self::ESTABLISHMENT_YEAR);
- $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
- $date->add(new DateInterval('P' . easter_days($year) . 'D'));
+ $date = $this->calculateEaster($year, self::TIMEZONE);
  $date->sub(new DateInterval('P2D'));
  $data[] = [$year, $date->format('Y-m-d')];
  }

tests/UnitedKingdom/EasterMondayTest.php

@@ -53,8 +53,8 @@ public function HolidayDataProvider()
 
  for ($y = 0; $y < 50; $y++) {
  $year = $this->generateRandomYear();
- $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
- $date->add(new DateInterval('P' . (easter_days($year) + 1) . 'D'));
+ $date = $this->calculateEaster($year, self::TIMEZONE);
+ $date->add(new DateInterval('P1D'));
 
  $data[] = [$year, $date->format('Y-m-d')];
  }

tests/YasumiBase.php

@@ -12,6 +12,7 @@
 
 namespace Yasumi\tests;
 
+use DateInterval;
 use DateTime;
 use DateTimeZone;
 use Faker\Factory as Faker;
@@ -219,4 +220,82 @@ public function generateRandomYear($lowerLimit = 1000, $upperLimit = 9999)
  {
  return (int)Faker::create()->numberBetween($lowerLimit, $upperLimit);
  }
+
+ /**
+ * Calculates the date for Easter.
+ *
+ * Easter is a festival and holiday celebrating the resurrection of Jesus Christ from the dead. Easter is celebrated
+ * on a date based on a certain number of days after March 21st.
+ *
+ * This function uses the standard PHP 'easter_days' function if the calendar extension is enabled. In case the
+ * calendar function is not enabled, a fallback calculation has been implemented that is based on the same
+ * 'easter_days' c function.
+ *
+ * Note: In calendrical calculations, frequently operations called integer division are used.
+ *
+ * @see easter_days
+ *
+ * @link https:/php/php-src/blob/c8aa6f3a9a3d2c114d0c5e0c9fdd0a465dbb54a5/ext/calendar/easter.c
+ * @link http://www.gmarts.org/index.php?go=415#EasterMallen
+ * @link http://www.tondering.dk/claus/cal/easter.php
+ *
+ * @param int $year the year for which Easter needs to be calculated
+ * @param string $timezone the timezone in which Easter is celebrated
+ *
+ * @return \DateTime date of Easter
+ */
+ protected function calculateEaster($year, $timezone)
+ {
+ if (extension_loaded('calendar')) {
+ $easter_days = \easter_days($year);
+ } else {
+ $golden = (int)(($year % 19) + 1); // The Golden Number
+
+ // The Julian calendar applies to the original method from 326AD. The Gregorian calendar was first
+ // introduced in October 1582 in Italy. Easter algorithms using the Gregorian calendar apply to years
+ // 1583 AD to 4099 (A day adjustment is required in or shortly after 4100 AD).
+ // After 1752, most western churches have adopted the current algorithm.
+ if ($year <= 1752) {
+ $dom = ($year + (int)($year / 4) + 5) % 7; // The 'Dominical number' - finding a Sunday
+ if ($dom < 0) {
+ $dom += 7;
+ }
+
+ $pfm = (3 - (11 * $golden) - 7) % 30; // Uncorrected date of the Paschal full moon
+ if ($pfm < 0) {
+ $pfm += 30;
+ }
+ } else {
+ $dom = ($year + (int)($year / 4) - (int)($year / 100) + (int)($year / 400)) % 7; // The 'Dominical number' - finding a Sunday
+ if ($dom < 0) {
+ $dom += 7;
+ }
+
+ $solar = (int)(($year - 1600) / 100) - (int)(($year - 1600) / 400); // The solar correction
+ $lunar = (int)(((int)(($year - 1400) / 100) * 8) / 25); // The lunar correction
+
+ $pfm = (3 - (11 * $golden) + $solar - $lunar) % 30; // Uncorrected date of the Paschal full moon
+ if ($pfm < 0) {
+ $pfm += 30;
+ }
+ }
+
+ // Corrected date of the Paschal full moon, - days after 21st March
+ if (($pfm == 29) || ($pfm == 28 && $golden > 11)) {
+ --$pfm;
+ }
+
+ $tmp = (4 - $pfm - $dom) % 7;
+ if ($tmp < 0) {
+ $tmp += 7;
+ }
+
+ $easter_days = (int)($pfm + $tmp + 1); // Easter as the number of days after 21st March
+ }
+
+ $easter = new DateTime("$year-3-21", new DateTimeZone($timezone));
+ $easter->add(new DateInterval('P' . $easter_days . 'D'));
+
+ return $easter;
+ }
 }