PHP internal hashCode Function

Question

I am looking for the PHP equelent to JAVA\'s

 \"SomeString\".hashCode();

function. The hashCode i am looking for should be the same which is u

Answer 1

Here is my 2 cents for implementing Java's hashCode in PHP:

/**
 * Simulates java hashCode function
 * hash a string to 32 bit
 * @param str the string to hash
 * @return hashed 32 bit integer
 */
function hashCode($str) {
    $str = (string)$str;
    $hash = 0;
    $len = strlen($str);
    if ($len == 0 )
        return $hash;

    for ($i = 0; $i < $len; $i++) {
        $h = $hash << 5;
        $h -= $hash;
        $h += ord($str[$i]);
        $hash = $h;
        $hash &= 0xFFFFFFFF;
    }
    return $hash;
};

Answer 2

Arkh and the github solution referenced by guiguoz are in the right direction, but both fail to take into account that PHP will upconvert the integer hash value to a double as soon as it exceeds 2^61. The java function, which is calculated using fixed hardware 32-bit signed values, involves 32-bit arithmetic overflow (intrinsic to the CPU) to keep the value as a 32-bit signed integer.

In PHP, you will need to manually perform that arithmetic overflow each time the $hash is updated:

function overflow32($v)
{
    $v = $v % 4294967296;
    if ($v > 2147483647) return $v - 4294967296;
    elseif ($v < -2147483648) return $v + 4294967296;
    else return $v;
}

function hashCode( $s )
{
    $h = 0;
    $len = strlen($s);
    for($i = 0; $i < $len; $i++)
    {
        $h = overflow32(31 * $h + ord($s[$i]));
    }

    return $h;
}

(edit: corrected %v typo)

Answer 3

There is no such method available in php. So you will have to implement the correct method. Wikipedia gives the algorithm used by Java.lang.hashCode which is used by strings I think, so here is a quick php version of it:

<?php
function getStringHashCode($string){
  $hash = 0;
  $stringLength = strlen($string);
  for($i = 0; $i < $stringLength; $i++){
    $hash = 31 * $hash + $string[$i];
  }
  return $hash;
}

Answer 4

spl_object_hash is probably the closest to what you want, but despite the name it does not really return a hash of the passed in value, merely an internal unique identifier. I don't know if it's the hash actually used under the hood for arrays etc.

Answer 5

a utf-8 version with emoji support

function str_hashcode($s){
    $hash = 0;
    $len = mb_strlen($s, 'UTF-8');
    if($len == 0 )
        return $hash;
    for ($i = 0; $i < $len; $i++) {
        $c = mb_substr($s, $i, 1, 'UTF-8');
        $cc = unpack('V', iconv('UTF-8', 'UCS-4LE', $c))[1];
        $hash = (($hash << 5) - $hash) + $cc;
        $hash &= $hash; // 16bit > 32bit
    }
    return $hash;
}