@Override
	public long subtract(Address addr1, Address addr2) {
		AddressSpace space1 = addr1.getAddressSpace();
		AddressSpace space2 = addr2.getAddressSpace();
		if (space1.equals(this)) {
			space1 = baseSpace;
		}
		if (space2.equals(this)) {
			space2 = baseSpace;
		}
		if (!space1.equals(space2)) {
			throw new IllegalArgumentException("Address are in different spaces " +
				addr1.getAddressSpace().getName() + " != " + addr2.getAddressSpace().getName());
		}
		return addr1.getOffset() - addr2.getOffset();
	}
Get the ordered key assigned to this overlay address space instance  This value is used
when performing {@link #equals(Object)} and {@link #compareTo(AddressSpace)}
operations.
<p>
If this value does not have its optimal value (i.e., same as address space name), the 
associated {@link AddressFactory} should report a 
{@link AddressFactory#hasStaleOverlayCondition() stale overlay condition}.
@return instance ordered key
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/model/address/OverlayAddressSpace.java