<?php
  function baseToDec($val){
    $baseStr = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $n = strlen($val);
    $b = strlen($baseStr);
    $s = 0;
   // var_dump($n);
    for ($i =0; $i < strlen($val); $i++){
      $n--;
      $s = $s + (strpos($baseStr,$val[$i])*($b**$n)); 
        // The non numerical values, such as E or Q could
       // not be multiplied, so we used its index in the $baseStr
    }
    return $s;
  }
  echo baseToDec('A11320');

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