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 used for indexing Hashmaps in PHP. I Hope you can help me :)

EDIT:

Okay found the function i was searching for its written in C and is not available in PHP itself but thanks for your help !

ulong zend_inline_hash_func(char *arKey, uint nKeyLength)
{
        ulong $h = 5381;
        char *arEnd = arKey + nKeyLength;

        while (arKey < arEnd) {
                $h += ($h << 5);
                $h += (ulong) *arKey++;
        }
        return $h;
}

Why are all the answers below using 31? Isn't $h += ($h << 5) equivalent to $h *= 33? — SOFe
– SOFe, Commented Dec 13, 2021 at 12:17

Patrick Plaggenborg · Accepted Answer · 2016-02-05 10:11:56Z

9

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)

edited Feb 5, 2016 at 10:11

Patrick Plaggenborg

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answered Mar 29, 2013 at 11:45

jshouchin

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4 Comments

xryl669 Over a year ago

The overflow32 method is wrong (%v instead of $v, and it divides by 0 on a 32bit machine). Instead, the $h = line should read:$h = (int)(31 * $h + ord($s[$i])) & 0xffffffff;

ahoo Over a year ago

@xryl669, your line will return wrong on hashCode("153193cc3139f12e"). it returns 3369976574 instead of -924990722.

SOFe Over a year ago

This is still not applicable for 32-bit systems.

SOFe Over a year ago

Is it possible to replace overflow32() with & 0x7FFFFFFF? Or would there be other issues?

Arkh · Accepted Answer · 2012-01-10 15:03:14Z

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;
}

answered Jan 10, 2012 at 15:03

Arkh

8,44043 silver badges47 bronze badges

2 Comments

user982911 Over a year ago

thx for this code but i need EXACTLY the same used internal for building hashmaps.

guigouz Over a year ago

This function is wrong, gist.github.com/andreyknupp/5061911 has a correct implementation, but it still yields different hashes if the String has spaces on it.

Community · Accepted Answer · 2023-11-17 20:29:45Z

1

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.

edited Nov 17, 2023 at 20:29

CommunityBot

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answered Jan 10, 2012 at 15:06

Rob Agar

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Comments

Yair · Accepted Answer · 2014-08-11 03:17:24Z

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;
};

answered Aug 11, 2014 at 3:17

Yair

192 bronze badges

Comments

0x00 · Accepted Answer · 2022-04-03 06:46:06Z

0

Not equal, but very fast:

function hashCode32Signed($str)
{
    return unpack('l', hash('crc32', $str, true))[1];
}

answered Apr 3, 2022 at 6:46

0x00

1

1 Comment

Community Over a year ago

Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.

Soyoes · Accepted Answer · 2016-11-19 03:37:23Z

-1

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;
}

answered Nov 19, 2016 at 3:37

Soyoes

94011 silver badges16 bronze badges

1 Comment

thelastshadow Over a year ago

This function returns the same hash for 'aaaa-bbbb-cccc-dddd-eeee-ffff-gggg-hhhh-iiii-jjjj-kkkk-11111' as 'aaaa-bbbb-cccc-dddd-eeee-ffff-gggg-hhhh-iiii-jjjj-kkkk-22222'. jshouchin's accepted answer also supports emoji's.

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