avr: added List_GetItemAt

avr/common/list.asm

@@ -241,6 +241,42 @@ List_ForEveryObject_callZ:
 
 
 
+; ---------------------------------------------------------------------------
+; @routine List_GetItemAt
+
+; @param  Y     pointer to first object in a list
+; @param  r16   idx (starting with 0)
+; @return CFLAG set if found, cleared otherwise
+; @return X     list element at given idx (if CFLAG set)
+; @clobbers r16, r17
+
+List_GetItemAt:
+  push yl
+    push yh
+      mov r17, yl
+      or r17, yh
+      clc
+      breq List_GetItemAt_done
+List_GetItemAtLoop:
+        tst r16
+        breq List_GetItemAt_found
+        ldd r17, Y+LIST_OFFS_NEXT_LO
+        ldd yh, Y+LIST_OFFS_NEXT_HI
+        mov yl, r17
+        or r17, yh
+        clc
+        breq List_GetItemAt_done
+        dec r16
+      rjmp List_GetItemAtLoop
+List_GetItemAt_found:
+      mov xl, yl
+      mov xh, yh
+      sec
+List_GetItemAt_done:
+    pop yh
+  pop yl
+  ret
+; @end