variable support cleanup

src/basic/engine_runtime/fetch_line_number.s

@@ -0,0 +1,21 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+//
+// Fetches line number, stores it in LINNUM, sets Carry to indicate failure (not a number)
+//
+// Preserves both .X and .Y
+//
+
+fetch_line_number:
+
+	lda #IDX__EV7_26 // 'LINE NUMBER TOO LARGE'
+	jsr fetch_uint16
+	bcs_16 do_SYNTAX_error
+
+	lda LINNUM+1
+	cmp #$FF
+	beq_16 do_LINE_NUMBER_TOO_LARGE_error
+
+	rts