A simple math function that computes the cardinal sine of a real number x. It computes the historical (unnormalized) cardinal sine by default, but if its second argument is set to SINC_NORMALIZED then it computes the normalized cardinal sine of x instead. A great complement to the math functions already available as part of the PHP Core.

function.sinc.php

<?php

/*
  function.sinc.php
  A simple math function (with input validation)
  that computes the cardinal sine of a real
  number $x
  Author: Donald Leung
  NOTE: Comes with two user-defined constants
*/

// Constants (for use by the sinc() function as flags)
define('SINC_DEFAULT', 0);
define('SINC_NORMALIZED', 1);

// Function declaration and definition
function sinc($x, $flag = SINC_DEFAULT) {
  // Type check "x" - confirm that it is either of an integer or a float
  if (!is_int($x) && !is_float($x)) throw new InvalidArgumentException('In sinc(), the first argument "x" passed in must either be an integer or a float');
  // Validate the flag - it can only be one of SINC_DEFAULT and SINC_NORMALIZED
  if ($flag !== SINC_DEFAULT && $flag !== SINC_NORMALIZED) throw new InvalidArgumentException('The sinc() function only accepts 2 possible flags: SINC_DEFAULT and SINC_NORMALIZED');
  // Special Case: where x = 0, sinc(x) = sinc(0) = 1
  if ($x == 0) return 1;
  // If the flag is set to SINC_NORMALIZED then multiply the argument "x" by pi and compute its unnormalized cardinal sine at pi * x
  if ($flag === SINC_NORMALIZED) return sinc(M_PI * $x);
  // Otherwise just return the unnormalized cardinal sine of x
  return sin($x) / $x;
}

?>