add column unique numbering scheme, more efficient selects

porklib/Utils/Utils.php

@@ -991,4 +991,26 @@ class Utils
 
         throw new FormatException("Bad time interval: \"$time\"");
     }
+
+    /**
+     * Convert number to arbitrary alphabet, using a system similar to EXCEL column numbering.
+     *
+     * @param int $n
+     * @param string[] $alphabet - array of characters to use
+     * @return string
+     */
+    public static function alphabetEncode($n, $alphabet)
+    {
+        $key = '';
+        $abcsize = count($alphabet);
+        $i = $n;
+
+        do {
+            $mod = $i % $abcsize;
+            $key = $alphabet[$mod] . $key;
+            $i = (($i - $mod) / $abcsize) - 1;
+        } while($i >= 0);
+
+        return $key;
+    }
 }