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<?php

function validateCC($ccnum){

// Clean up input  
    $ccnum = ereg_replace('[-[:space:]]', '',$ccnum);

// What kind of card do we have
    $type = check_type($ccnum);

// Does the number matchup ?
    $valid = check_number($ccnum);

return array($type, $valid);

}

// Prefix and Length checks
function check_type( $cardnumber ) {

$cardtype = "UNKNOWN";

$len = strlen($cardnumber);
   if     ( $len == 15 && substr($cardnumber, 0, 1) == '3' )                 { $cardtype = "amex"; }
   elseif ( $len == 16 && substr($cardnumber, 0, 4) == '6011' )              { $cardtype = "discover"; }
   elseif ( $len == 16 && substr($cardnumber, 0, 1) == '5'  )                { $cardtype = "mc"; }
   elseif ( ($len == 16 || $len == 13) && substr($cardnumber, 0, 1) == '4' ) { $cardtype = "visa"; }

return ( $cardtype );

}

// MOD 10 checks 
function check_number( $cardnumber ) {

$dig = toCharArray($cardnumber); 
 $numdig = sizeof ($dig); 
 $j = 0; 
 for ($i=($numdig-2); $i>=0; $i-=2){ 
 $dbl[$j] = $dig[$i] * 2; 
 $j++; 
 } 
 $dblsz = sizeof($dbl); 
 $validate =0; 
 for ($i=0;$i<$dblsz;$i++){ 
 $add = toCharArray($dbl[$i]); 
 for ($j=0;$j<sizeof($add);$j++){ 
 $validate += $add[$j]; 
 } 
 $add = ''; 
 } 
 for ($i=($numdig-1); $i>=0; $i-=2){ 
 $validate += $dig[$i]; 
 } 
 if (substr($validate, -1, 1) == '0') { return 1; }
 else { return 0; }
}

// takes a string and returns an array of characters

function toCharArray($input){ 
 $len = strlen($input); 
 for ($j=0;$j<$len;$j++){ 
 $char[$j] = substr($input, $j, 1); 
 } 
 return ($char); 
}

$ccnumber = '5105105105105100';
 list($type, $valid) = validateCC($ccnumber);
 if ( $valid ) { 
 // Do something fun with the card
 echo "Number: $ccnumber ... Type: $type ... Valid: $valid ";
 }
 else { 
 // Return some sort of error
 }

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