optimization in variable search

src/basic/engine_variables/helper_cmp_varnam_46K_50K.s

@@ -0,0 +1,38 @@
+// #LAYOUT# STD *       #TAKE-HIGH
+// #LAYOUT# *   BASIC_0 #TAKE-HIGH
+// #LAYOUT# *   *       #IGNORE
+
+// This has to go $E000 or above - routines below banks out the main BASIC ROM!
+
+#if CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+
+helper_cmp_varnam:
+
+	// Unmap BASIC lower ROM
+
+	lda #$26
+	sta CPU_R6510
+
+	// Compare variable name
+
+	ldy #$00
+	lda (VARPNT),y
+
+	cmp VARNAM+0
+	bne !+
+
+	iny
+	lda (VARPNT),y
+	cmp VARNAM+1
+!:
+	// Restore default memory mapping
+	// XXX consider deduplicating with 'is_line_pointer_null'
+
+	php
+	lda #$27
+	sta CPU_R6510
+	plp
+
+	rts
+
+#endif