avr: simplify handling of object tree

- set CFLAG if pointer valid, cleared otherwise
- check for inbound NULL pointer

avr/modules/lcd2/gui2/object.asm

@@ -57,14 +57,30 @@
 ; @routine OBJ_GetParent @global
 ;
 ; @param Z byte address of object (for LPM!)
+; @return CFLAG set, if found, cleared otherwise
 ; @return r19:r18 resulting object (byte address for LPM!), NULL otherwise
 ; @clobbers none
 
 OBJ_GetParent:
+  tst zh
+  brne OBJ_GetParent_get
+  tst zl
+  brne OBJ_GetParent_get
+  clc
+  rjmp OBJ_GetParent_ret
+OBJ_GetParent_get:
   adiw zh:zl, OBJECT_OFFS_PARENT_LO
   lpm r18, Z+
   lpm r19, Z
   sbiw zh:zl, (OBJECT_OFFS_PARENT_LO+1)
+  tst r18
+  brne OBJ_GetParent_secRet
+  tst r19
+  clc
+  breq OBJ_GetParent_ret
+OBJ_GetParent_secRet:
+  sec
+OBJ_GetParent_ret:
   ret
 ; @end
 
@@ -74,14 +90,30 @@ OBJ_GetParent:
 ; @routine OBJ_GetFirstChild @global
 ;
 ; @param Z byte address of object (for LPM!)
+; @return CFLAG set, if found, cleared otherwise
 ; @return r19:r18 resulting object (byte address for LPM!), NULL otherwise
 ; @clobbers none
 
 OBJ_GetFirstChild:
+  tst zh
+  brne OBJ_GetFirstChild_get
+  tst zl
+  brne OBJ_GetFirstChild_get
+  clc
+  rjmp OBJ_GetFirstChild_ret
+OBJ_GetFirstChild_get:
   adiw zh:zl, OBJECT_OFFS_CHILD_LO
   lpm r18, Z+
   lpm r19, Z
   sbiw zh:zl, OBJECT_OFFS_CHILD_LO+1
+  tst r18
+  brne OBJ_GetFirstChild_secRet
+  tst r19
+  clc
+  breq OBJ_GetFirstChild_ret
+OBJ_GetFirstChild_secRet:
+  sec
+OBJ_GetFirstChild_ret:
   ret
 ; @end
 
@@ -91,14 +123,30 @@ OBJ_GetFirstChild:
 ; @routine OBJ_GetNext @global
 ;
 ; @param Z byte address of object (for LPM!)
+; @return CFLAG set, if found, cleared otherwise
 ; @return r19:r18 resulting object (byte address for LPM!), NULL otherwise
 ; @clobbers none
 
 OBJ_GetNext:
+  tst zh
+  brne OBJ_GetNext_get
+  tst zl
+  brne OBJ_GetNext_get
+  clc
+  rjmp OBJ_GetNext_ret
+OBJ_GetNext_get:
   adiw zh:zl, OBJECT_OFFS_NEXT_LO
   lpm r18, Z+
   lpm r19, Z
   sbiw zh:zl, OBJECT_OFFS_NEXT_LO+1
+  tst r18
+  brne OBJ_GetNext_secRet
+  tst r19
+  clc
+  breq OBJ_GetNext_ret
+OBJ_GetNext_secRet:
+  sec
+OBJ_GetNext_ret:
   ret
 ; @end
 
@@ -108,38 +156,30 @@ OBJ_GetNext:
 ; @routine OBJ_GetBelow @global
 ;
 ; @param Z byte address of object (for LPM!)
+; @return CFLAG set, if found, cleared otherwise
 ; @return r19:r18 resulting object (byte address for LPM!), NULL otherwise
 ; @clobbers r16
 
 OBJ_GetBelow:
-  ; check first child
+  tst zh
+  brne OBJ_GetBelow_get
+  tst zl
+  breq OBJ_GetBelow_ret
+OBJ_GetBelow_get:
   rcall OBJ_GetFirstChild
-  mov r16, r18
-  or r16, r19
-  sec
-  brne OBJ_GetBelow_ret
-  ; check neighbour
+  brcs OBJ_GetBelow_ret    ; jmp if found
   rcall OBJ_GetNext
-  mov r16, r18
-  or r16, r19
-  sec
-  brne OBJ_GetBelow_ret
+  brcs OBJ_GetBelow_ret    ; jmp if found
 
 OBJ_GetBelow_loop:
     rcall OBJ_GetParent
-    mov r16, r18
-    or r16, r19
-    clc
-    breq OBJ_GetBelow_ret
+    brcc OBJ_GetBelow_ret  ; jmp if no parent
     ; use parent
     mov zl, r18
     mov zh, r19
     ; don't check for first child here, we came from there!
     rcall OBJ_GetNext
-    mov r16, r18
-    or r16, r19
-    sec
-    brne OBJ_GetBelow_ret
+    brcs OBJ_GetBelow_ret
   rjmp OBJ_GetBelow_loop
 OBJ_GetBelow_ret:
   ret