code: private int zoneOffsetAt(int transIdx) {
          int typeIdx = transIdx >= 0 ? getInt(typeMapData[transIdx]) * 2 : 0;
          return typeOffsets[typeIdx] + typeOffsets[typeIdx + 1];
      }
docs: /*
  Following 3 methods return an offset at the given transition time index.
  When the index is negative, return the initial offset.