variable support cleanup

src/basic/engine_runtime/is_alphanumeric.s

@@ -0,0 +1,39 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# M65 BASIC_1 #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+//
+// Check .A content, if within 0-9, A-Z ranges, sets Carry if check fails
+//
+
+
+is_09_AZ:
+
+	jsr is_AZ
+	bcs is_09
+	rts
+
+
+is_09:
+
+	cmp #$30                                 // if below '0' - check failed
+	bcc is_alphanumeric_fail
+
+	cmp #$3A                                 // if above '9' - check failed
+	rts
+
+
+is_AZ:
+
+	cmp #$41                                 // if below 'A' - check failed
+	bcc is_alphanumeric_fail
+
+	cmp #$7B                                 // if above 'Z' - check failed
+	rts
+
+
+is_alphanumeric_fail:
+
+	sec
+	rts