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for PHP: validate input and support integers up to PHP_INT_MAX #11

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for PHP: validate input and support integers up to PHP_INT_MAX #11

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73 changes: 66 additions & 7 deletions PHP/ShortURL.php
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Original file line number Diff line number Diff line change
Expand Up @@ -26,25 +26,84 @@ class ShortURL {
const BASE = 51; // strlen(self::ALPHABET)

public static function encode($num) {
$num = filter_var ( $num, FILTER_VALIDATE_INT, array (
'options' => array (
'default' => false,
'min_range' => 1,
'max_range' => PHP_INT_MAX
)
) );
if ($num === false) {
throw new InvalidArgumentException ( 'input MUST be an int between 1 and ' . PHP_INT_MAX . ' (PHP_INT_MAX).' );
}
$str = '';

while ($num > 0) {
$str = self::ALPHABET[($num % self::BASE)] . $str;
$num = (int) ($num / self::BASE);
while ( $num > 0 ) {
$str = self::ALPHABET [($num % self::BASE)] . $str;
if($num <= 0x7FFFFFFF){
//the number is so small that using regular php division is safe (and fastest)
$num = (int) ($num / self::BASE);
} else if (is_callable ( 'bcdiv' )) {
// use bcmath if available. should be faster than userland php division. could add GMP support.
$num = ( int ) bcdiv ( $num, self::BASE, 0 );
} else {
//fallback to userland php division
$num = self::saferudiv ( $num, self::BASE );
}
}

return $str;
}

public static function decode($str) {
$num = 0;
$len = strlen($str);
$len = strlen ( $str );

for ($i = 0; $i < $len; $i++) {
$num = $num * self::BASE + strpos(self::ALPHABET, $str[$i]);
for($i = 0; $i < $len; $i ++) {
$num = $num * self::BASE + strpos ( self::ALPHABET, $str [$i] );
}

return $num;
}

private static function saferudiv(/*int */$N,/* int */$D) {
// based on an algorithm from http://justinparrtech.com/JustinParr-Tech/an-algorithm-for-arbitrary-precision-integer-division/
$N = ( int ) abs ( ( int ) $N );
$D = ( int ) abs ( ( int ) $D );
$M = strlen ( ( string ) $D ) - 1;
// assert($N===999999);
// assert($D===7777);
// assert($M===3);
$A = ( int ) ($D - (( int ) ($D % (( int ) pow ( $M, 10 )))));
// assert($A===7000);
$Q = ( int ) self::_saferudiv ( $N, $A, 0 );
// assert($Q===142);
$R = ( int ) ($D + 1);
// assert($R===7778);
while ( (( int ) abs ( $R )) >= $D ) {
$R = ( int ) ($N - (( int ) ($Q * $D)));
$Qn = ( int ) ($Q + (( int ) (self::_saferudiv ( $R, $A ))));
$Q = ( int ) (self::_saferudiv ( ( int ) ($Q + $Qn), 2 ));
}
$R = ( int ) ($N - (( int ) ($Q * $D)));
// assert($R===-3234);
if ($R < 0) {
$Q = ( int ) ($Q - 1);
// assert($Q===128);
$R = ( int ) ($R + $D);
// assert($R===4543);
}
// assert(999999===($Q*$D+$R));
// var_dump ( $Q, $R );
return $Q;
}
private static function _saferudiv($x, $y, $unused = NULL) {
if (PHP_INT_SIZE === 4) {
return ( int ) ($x / $y);
} elseif (PHP_INT_SIZE === 8) {
return ($x - ($x % $y)) / $y;
} else {
// running 128bit php or something?
throw new Exception ( 'this code only supports 4 bytes (32bit) and 8 bytes (64bit) php integers, but this php runtime uses ' . PHP_INT_SIZE . ' bytes integers. the code needs to get updated.' );
}
}
}