EAN, EAN-8, EAN-13, GTIN-8, GTIN-12, GTIN-14, UPC, UPC-12 coupon code, JAN 

function is_valid_barcode($code)
{
    $types = array("EAN2", "EAN5", "EAN8", "EAN13", "UPCA", "UPCE", "C39", "C39+", "C39E", "C39E+", "I25", 
        "C128A", "C128B", "C128C", "POSTNET", "CODABAR");

    foreach ($types as $type)
    {
        if (substr($type, 0, 3) === "EAN" || substr($type, 0, 3) == "UPC")
        {
            if (!preg_match("/^[0-9]+$/", $code))
                continue;
        }        
           $barcode = new TCPDFBarcode($code, $type);
        $chk = $barcode->getBarcodeArray();
        if ($chk !== false)
            return true;
    }
    return false;
}

include $path_to_root."reporting/includes/barcode.php";

function is_valid_barcode($code, $type) {
    $barcode = new TCPDFBarcode($code, $type);
    $chk = $barcode->getBarcodeArray();
    return ($chk !== false);
}

$barcode['C39']['name']     = 'CODE 39';
$barcode['C39+']['name']    = 'CODE 39 with checksum';
$barcode['C39E']['name']    = 'CODE 39 EXTENDED';
$barcode['C39E+']['name']   = 'CODE 39 EXTENDED with checksum';
$barcode['I25']['name']     = 'Interleaved 2 of 5';
$barcode['C128A']['name']   = 'CODE 128 A';
$barcode['C128B']['name']   = 'CODE 128 B';
$barcode['C128C']['name']   = 'CODE 128 C';
$barcode['EAN2']['name']    = '2-Digits UPC-Based Extension';
$barcode['EAN5']['name']    = '5-Digits UPC-Based Extension';
$barcode['EAN8']['name']    = 'EAN 8';
$barcode['EAN13']['name']   = 'EAN 13';
$barcode['UPCA']['name']    = 'UPC-A';
$barcode['UPCE']['name']    = 'UPC-E';
$barcode['POSTNET']['name'] = 'POSTNET';
$barcode['CODABAR']['name'] = 'CODABAR';

<?php
/* Check length of barcode for validity via the checkdigit calculation
 * We split the barcode into it's constituent digits, offset them into the GTIN
 * calculation tuple (x1, x3, x1, x3, x1, etc, etc), multiply the digits and add
 * them together, then modulo them on 10, and you get the calculated check digit.
 * For more information see GS1 website: https://www.gs1.org/check-digit-calculator
 * @param string gtin
 * @return bool */
function Checkgtin($gtin) 
{
    /* Checks the length of the GTIN
     * @param string gtin
     * @return bool */
    // Check length is ok
    if (strlen($gtin) < 8 || strlen($gtin) > 14)
        return false;

    // Check whether is a number
    preg_match("/\d+/", $gtin, $m, PREG_OFFSET_CAPTURE, 0);
    if (empty($m))
        return false;

    // Define fixed variables
    $CheckDigitArray = [];
    $gtinMaths = [3, 1, 3, 1, 3, 1, 3, 1, 3, 1, 3, 1, 3, 1, 3, 1, 3];
    $modifier = 17 - (strlen($gtin) - 1);  // Gets the position to place first digit in array
    $gtinCheckDigit = substr($gtin, -1); // Get provided check digit
    $BarcodeArray = str_split($gtin);  // Split barcode at each digit into array
    $gtinLength = strlen($gtin);
    $tmpCheckDigit = 0;
    $tmpCheckSum = 0;
    $tmpMath = 0;

    // Run through and put digits into multiplication table
    for ($i = 0; $i < ($gtinLength - 1); $i++) {
        $CheckDigitArray[$modifier + $i] = $BarcodeArray[$i];  // Add barcode digits to Multiplication Table
    }

    // Calculate "Sum" of barcode digits
    for ($i = $modifier; $i < 17; $i++) {
        $tmpCheckSum += ($CheckDigitArray[$i] * $gtinMaths[$i]);
    }

    // Difference from Rounded-Up-To-Nearest-10 - Fianl Check Digit Calculation
    $tmpCheckDigit = (ceil($tmpCheckSum / 10) * 10) - $tmpCheckSum;

    // Check if last digit is same as calculated check digit
    if ($gtinCheckDigit == $tmpCheckDigit)
        return true;
    return false;
}
  
$gtin = "00abcd";
if (Checkgtin($gtin))
    echo "$gtin is ok<br />";
else    
    echo "$gtin is NOT ok<br />";