more work on inserting and deleting BASIC lines.

c64/basic/peek_pointer_null_check.s

@@ -0,0 +1,18 @@
+	;; Return C=1 if a pointer in BASIC memory space is NULL, else C=0
+	;; X = ZP pointer to check
+
+peek_pointer_null_check:
+	ldy #$00
+	jsr peek_under_roms
+	bne ptr_not_null
+	iny
+	jsr peek_under_roms
+	bne ptr_not_null
+
+	;; Pointer is NULL
+	clc
+	rts
+ptr_not_null:
+	sec
+	rts
+