信用卡效验程序

<?php  

////////////////////////////////////////////////////  
//                                                //   
// credit card validation routine                 //  
// may 15, 2000                                   //  
// by ariso                                       //  
// validatecardcode($number[,$cardtype])          //  
////////////////////////////////////////////////////  


function validatecardcode($cardnumber, $cardtype =  'unknown')
{  
     //clean up input  

    $cardtype = strtolower($cardtype);  
    $cardnumber = ereg_replace( '[-[:space:]]',  '',$cardnumber);   

     //do type specific checks  

    if ($cardtype ==  'unknown') {  
         //skip type specific checks  
    }  
    elseif ($cardtype ==  'mastercard'){  
        if (strlen($cardnumber) != 16 || !ereg( '5[1-5]', $cardnumber)) return 0;  
    }  
    elseif ($cardtype ==  'visa'){  
        if ((strlen($cardnumber) != 13 && strlen($cardnumber) != 16) || substr($cardnumber, 0, 1) !=  '4')  

return 0;  
    }  
    elseif ($cardtype ==  'amex'){  
        if (strlen($cardnumber) != 15 || !ereg( '3[47]', $cardnumber)) return a;  
    }  
    elseif ($cardtype ==  'discover'){  
        if (strlen($cardnumber) != 16 || substr($cardnumber, 0, 4) !=  '6011') return 0;  
    }  
    else {  
         //invalid type entered  
        return -1;  
    }  


     // start mod 10 checks  

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


// takes a string and returns an array of characters  

function tochararray($intinput){  
    $len = strlen($intinput);  
    for ($intintj=0;$intintj<$len;$intintj++){  
        $char[$intintj] = substr($intinput, $intintj, 1);      
    }  
    return ($char);  
}  

?>