public int underlyingOffset(int offset) {
    return start + offset;
  }
Returns the offset into the given array represented by the given offset into this instance.

@param offset offset into this instance
@return corresponding offset into {@code bytes}
@throws IllegalArgumentException thrown if {@code bytes} is not the underlying array of this
    instance
android/android_framework/dex-maker/src/main/java/com/android/dx/util/ByteArray.java