base 62 encode / decode

base62.php

function base62_encode($num) {
  $b = 62;
  $base = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
  $r = $num % $b ;
  $res = $base[$r];
  $q = floor($num/$b);
  
  while ($q) {
    $r = $q % $b;
    $q = floor($q/$b);
    $res = $base[$r].$res;
  }
  
  return $res;
}

function base62_decode( $num) {
  $b = 62;
  $base = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
  $limit = strlen($num);
  $res = strpos($base,$num[0]);
  
  for($i=1;$i<$limit;$i++) {
    $res = $b * $res + strpos($base,$num[$i]);
  }
  
  return $res;
}

echo base62_encode(68).PHP_EOL;
echo base62_decode('ghYU45').PHP_EOL;