Explain keypad number conversions in jni_ConvertToJavaLocation(...)

[spxl]

// FIXME Should this fall though? comments are highly suspicious. It seems that there should not be a fall-through in these places.

Please describe the logic of the subtractions made for numpad keys 1 to 9

eg
*nativeKeyCode -= ((VC_KP_1 - VC_1) - (VC_KP_4 - VC_4) ); // 0x4D - 0x46

Why are these not all just like the code for keypad 0?

jnativehook/src/main/jni/jni_Converter.c

Lines 142 to 166 in dd4a524

	case VC_KP_0:
	*nativeKeyCode = VC_0;
	*javaKeyLocation = com_github_kwhat_jnativehook_keyboard_NativeKeyEvent_LOCATION_NUMPAD;
	break;
	case VC_KP_1:
	case VC_KP_2:
	case VC_KP_3:
	*nativeKeyCode -= ((VC_KP_1 - VC_1) - (VC_KP_4 - VC_4) ); // 0x4D - 0x46
	// FIXME Should this fall though?
	/* fall-thru */
	case VC_KP_4:
	case VC_KP_5:
	case VC_KP_6:
	*nativeKeyCode -= ((VC_KP_4 - VC_4) - (VC_KP_7 - VC_7) ); // 0x46 - 0x3F
	// FIXME Should this fall though?
	/* fall-thru */
	case VC_KP_7:
	case VC_KP_8:
	case VC_KP_9:
	*nativeKeyCode -= (VC_KP_7 - VC_7); // 0x3F
	*javaKeyLocation = com_github_kwhat_jnativehook_keyboard_NativeKeyEvent_LOCATION_NUMPAD;
	break;