private int backupToFirstComponentContainingOffset(int index, int offset) {
		if (index == 0) {
			return 0;
		}
		while (index != 0) {
			DataTypeComponentImpl previous = components.get(index - 1);
			if (!previous.containsOffset(offset)) {
				break;
			}
			--index;
		}
		return index;
	}
Backup from specified defined-component index to the first component which contains the specified offset. 
@param index any defined component index which contains offset
@param offset offset within structure
@return index of first defined component containing specific offset.
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/model/data/StructureDataType.java