A strong hashing function

hash.php

<?php
/**
 * This function is distributed under the MIT Open Source License.
 * @author Ioan CHIRIAC
 * @link https://github.com/ichiriac
 */
function generate_password($password, $salt = 'your-secret-salt', $algo = 'sha256')
{
    // split the password
    $password = str_split($password, ceil(strlen($password)/2));
    // make a variable length salt
    $salt = 
          $password[0] 
        . hash($algo, $password[0]) 
        . $salt 
        . hash($algo, $password[1])
        . $password[1]
    ;
    // split the salt into 2 parts
    $salt = str_split($salt,ceil(strlen($salt)/2));
    // generating the hash with variable length generated salt
    return hash(
        $algo,
          $salt[0]
        . $password[0] 
        . $salt[1]
        . $password[1]
    );
}

Usage :
echo generate_password('test', 'secret', 'sha256');

Advantages :

• This function is safe from generated rainbow tables
• It costs 3x times more to generate a rainbow table (using 3 hash functions)
• The salt is hidden from hashes