Stage0/Library function prototypes/add_node.s

; Copyright (C) 2016 Jeremiah Orians
; This file is part of stage0.
;
; stage0 is free software: you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation, either version 3 of the License, or
; (at your option) any later version.
;
; stage0 is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
; GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with stage0.  If not, see <http://www.gnu.org/licenses/>.


;; add_node Function
;; Receives pointers in R0 R1
;; Alters R0 if NULL
;; Appends nodes together
;; Returns to whatever called it
:add_node
	;; Preserve Registers
	PUSHR R2 R15
	PUSHR R1 R15
	PUSHR R0 R15

	;; Handle if Head is NULL
	JUMP.NZ R0 @add_node_0
	POPR R0 R15
	PUSHR R1 R15
	JUMP @add_node_2

:add_node_0
	;; Handle if Head->next is NULL
	LOAD32 R2 R0 0
	JUMP.NZ R2 @add_node_1
	;; Set head->next = p
	STORE32 R1 R0 0
	;; Set p->prev = head
	STORE32 R0 R1 4
	JUMP @add_node_2

:add_node_1
	;; Handle case of Head->next not being NULL
	LOAD32 R0 R0 0              ; Move to next node
	LOAD32 R2 R0 0              ; Get node->next
	CMPSKIPI.E R2 0             ; If it is not null
	JUMP @add_node_1            ; Move to the next node and try again
	JUMP @add_node_0            ; Else simply act as if we got this node
	                            ; in the first place

:add_node_2
	;; Restore registers
	POPR R0 R15
	POPR R1 R15
	POPR R2 R15
	RET R15