fix several bugs with storing BASIC lines

c64/basic/basic_find_line.s

@@ -10,38 +10,49 @@ basic_find_line:
 
 basic_find_line_loop:	
 	;; Then search for line number
-	;; Line number 
+	;; Line number
+	
 	ldy #3
 	ldx #<basic_current_line_ptr
 	jsr peek_under_roms
 	cmp basic_line_number+1
+	beq +
 	bcs line_num_too_high
 	bne not_this_line
+*
+	
 	dey
 	jsr peek_under_roms
 	cmp basic_line_number+0
+	beq +
 	bcs line_num_too_high
 	bne not_this_line
-
+*
 	clc
 	rts
 not_this_line:
 	;; Not this line, so advance to next line
-	ldy #0
 	ldx #<basic_current_line_ptr
 	jsr peek_pointer_null_check
 	bcs more_lines_exist
 
 	;; no more lines exist, return failure
-line_num_too_high:	
+line_num_too_high:
 	sec
 	rts
 more_lines_exist:	
-	;; A = high byte of line
-	pha
-	dey
+
+	;; XXX - Add program mangled check here to be triggered
+	;; if the link goes backwards.
+	;; Follow link to next line
+	ldy #0
+	ldx #<basic_current_line_ptr
+	jsr peek_under_roms
+	sta $0100
+	iny
 	jsr peek_under_roms
-	sta basic_current_line_ptr+0
-	pla
 	sta basic_current_line_ptr+1
+	lda $0100
+	sta basic_current_line_ptr+0
+
 	jmp basic_find_line_loop