user982911 user982911 - 21 days ago 6
PHP Question

PHP internal hashCode Function

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;
}

Answer

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)