Check if Ether address is valid (a PHP implementation of the Ethereum Web3 API's isAddress() method). Credits to @tormuto.

EtherValidate.php

<?php

/**
 * Checks if the given string is an address
 *
 * @param String $address the given HEX adress
 * @return Boolean
*/
function isAddress($address) {
    if (!preg_match('/^(0x)?[0-9a-f]{40}$/i',$address)) {
        // Check if it has the basic requirements of an address
        return false;
    } elseif (preg_match('/^(0x)?[0-9a-f]{40}$/',$address) || preg_match('/^(0x)?[0-9A-F]{40}$/',$address)) {
        // If it's all small caps or all all caps, return true
        return true;
    } else {
        // Otherwise check each case
        return isChecksumAddress($address);
    }
}

/**
 * Checks if the given string is a checksummed address
 *
 * @param String $address the given HEX adress
 * @return Boolean
*/
function isChecksumAddress($address) {
    // Check each case
    $address = str_replace('0x','',$address);
    $addressHash = hash('sha3',strtolower($address));
    $addressArray=str_split($address);
    $addressHashArray=str_split($addressHash);

    for($i = 0; $i < 40; $i++ ) {
        // The nth letter should be uppercase if the nth digit of casemap is 1
        if ((intval($addressHashArray[$i], 16) > 7 && strtoupper($addressArray[$i]) !== $addressArray[$i]) || (intval($addressHashArray[$i], 16) <= 7 && strtolower($addressArray[$i]) !== $addressArray[$i])) {
            return false;
        }
    }
    
    return true;
}

PHP hash() function does not support SHA3 algorithm. Use "sha3-256" instead (it's available from PHP 7.1.0).

both sha or sha3-256 is incorrect.

and what would be correct?