Basic input validation for generating an index from a string

This method gets used by FakeReader to count the number of rows in a plate
based on the well name, so input should be the well row label, e.g. "A", "AC".

Author: melissalinkert

components/formats-bsd/src/loci/formats/ResourceNamer.java

@@ -139,8 +139,14 @@ public String getLetter() {
   public static int alphabeticIndexCount(String index) {
     int count = 0;
     char[] letters = index.toCharArray();
+    if (letters.length > 6) {
+      // this will cause an integer overflow
+      throw new IllegalArgumentException("Cannot count more than 6 characters");
+    }
     for (int i = 0; i < letters.length; i++) {
-      count += (letters[i] - 64) * Math.pow(ALPHABET_LENGTH, i);
+      int letterIndex = (int) Math.pow(ALPHABET_LENGTH, i);
+      int letterValue = letterIndex * (letters[i] - 64);
+      count += letterValue;
     }
     return count;
   }