## mark a section (Learn more)

<?php /** * @class Integer * @author Julien Garand (Go On Web) * * Can encode and decode integers to/from a string, using a custom alphabet */ class Integer { // Default alphabet for a "normal" base 62 encoding static protected $alphabet = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'; static protected $base = 62; /** * Define your custom alphabet here */ static public function setAlphabet( $alphabet ) { // only strings are allowed if ( !is_string($alphabet) ) { throw new Exception('Given alphabet is not a string !'); } self::$base = strlen( $alphabet ); // Our base will be the length of the given alphabet // We check if alphabet doesn't have doubled characters if ( strlen( count_chars( $alphabet, 3 ) ) != self::$base ) { throw new Exception('The following alphabet has doubled characters : '.$alphabet); } self::$alphabet = $alphabet; // store it } /** * Basic accessors */ static public function getAlphabet() { return self::$alphabet; } static public function getBase() { return self::$base; } /** * Encode an integer according to the defined alphabet * * @param integer : Unsigned integer to be encoded * @return string (or false if failed) */ static public function encode( $integer ) { $integer = (int)$integer; // Be sure to have an integer // We only accept unsigned integers if ( $integer < 0 ) { return false; // or throw new Exception( "($integer) is less than 0 and cannot be converted" ); } $string = ''; // our encoded integer // while we have to encode while( $integer ) { $pos = $integer % self::$base; // get the rest of euclidian division... $string .= self::$alphabet[ $pos ]; // thats the position of the char in alphabet $integer = ( $integer - $pos ) / self::$base; // and divide integer (minus just encoded char) by the base } return strrev( $string ); // As we started by the unit of our base ( $base ^ 0 ), we have to reverse the string } /** * Decode a string to an integer according to the defined alphabet * * @param string : String to be decoded * @return integer (or false if failed) */ static public function decode( $string ) { $string = (string)$string; // be sure to have a string; // check if our string only have chars that are in the alphabet if ( strcspn( $string, self::$alphabet ) ) { return false; // or throw new Exception( "($string) is not a string or contains characters that are not in alphabet" ); } $integer = 0; // our integer to find $unit = 1; // we start by $base^0 // foreach chars, starting at the end for( $i = strlen( $string ) -1; $i >= 0; $i -- ) { $pos = strpos( self::$alphabet, $string[$i] ); // we find it's position in alphabet $integer += $pos * $unit; // its our number to add, multiplied by the current unit $unit = $unit * self::$base; // and go to next unit in our base } return $integer; } }

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