code: public int lookupIndex(float value, float delta) {
          for (int i=0; i<size; i++) {
              if (Primitives.equals(elements[i + start], value, delta)) {
                  return i;
              }
          }
          return -1;
      }
docs: Gets the index of the first element in this vector with the specified
  value, or -1 if it is not present.
  
  @param value The value to search for.
  @param delta The delta with which to evaluate equality.
  @return The index or -1 if not present.