Hex impl with -state

static int
BinaryEncodeHex(ClientData clientData, Tcl_Interp *interp, 
    int objc, Tcl_Obj *const objv[])
{
    Tcl_Obj *resultObj = NULL;
    Tcl_Obj *stateObj = NULL;
    Tcl_Obj *statevarObj = NULL;
    unsigned char *data = NULL, *input = NULL, *state = NULL;
    unsigned char *cursor = NULL;
    const char *digits = clientData;
    int i, index, offset = 0, count = 0, state_count = 0;
    enum {OPT_STATE};
    static const char *optStrings[] = { "-state", NULL };
	
    if (objc < 2 || objc%2 != 0) {
	Tcl_WrongNumArgs(interp, 1, objv, "?-state varname? data");
	return TCL_ERROR;
    }
    for (i = 1; i < objc-1; i += 2) {
	if (Tcl_GetIndexFromObj(interp, objv[i], optStrings, 
		"option", TCL_EXACT, &index) != TCL_OK) {
	    return TCL_ERROR;
	}
	switch (index) {
	    case OPT_STATE: {
		statevarObj = objv[i+1];
		stateObj = Tcl_ObjGetVar2(interp, statevarObj, 
		    NULL, TCL_LEAVE_ERR_MSG);
		if (stateObj == NULL) {
		    return TCL_ERROR;
		}
		break;
	    }
	}
    }

    TclNewObj(resultObj);
    data = input = Tcl_GetByteArrayFromObj(objv[objc-1], &count);
    if (stateObj) {
	data = state = Tcl_GetByteArrayFromObj(stateObj, &state_count);
	count += state_count;
    }
    cursor = Tcl_SetByteArrayLength(resultObj, count * 2);
    for (offset = 0; offset < count; ++offset) {
	if (state && offset >= state_count) {
	    data = input;
	    state = NULL;
	}
	*cursor++ = digits[((*data >> 4) & 0x0f)];
	*cursor++ = digits[( *data       & 0x0f)];
	++data;
    }
    if (statevarObj) {
	/*
	 * the hex encoding never has any data left over so we always
	 * set the state to an empty byte array.
	 */
	Tcl_Obj *excessObj = Tcl_NewByteArrayObj(NULL, 0);
	Tcl_ObjSetVar2(interp, statevarObj, NULL, excessObj, 0);
    }
    Tcl_SetObjResult(interp, resultObj);
    return TCL_OK;
}