optimization in variable search

src/basic/engine_variables/fetch_variable.s

@@ -130,13 +130,15 @@ fetch_variable_find_addr_loop:
 	// Compare current variable name with searched one
 	// XXX consider creating optimized version for 46K/50K memory models
 
+#if CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+	jsr helper_cmp_varnam
+#else
+
 	ldy #$00
 
 #if CONFIG_MEMORY_MODEL_60K
 	ldx #<VARPNT
 	jsr peek_under_roms
-#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
-	jsr peek_under_roms_via_VARPNT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (VARPNT),y
 #endif
@@ -148,13 +150,14 @@ fetch_variable_find_addr_loop:
 
 #if CONFIG_MEMORY_MODEL_60K
 	jsr peek_under_roms
-#elif CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
-	jsr peek_under_roms_via_VARPNT
 #else // CONFIG_MEMORY_MODEL_38K
 	lda (VARPNT),y
 #endif
 
 	cmp VARNAM+1
+
+#endif
+
 	bne fetch_variable_find_addr_next
 
 	// FALLTROUGH

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

src/basic/engine_variables/helper_strdesccpy_46K_50K.s

@@ -2,7 +2,7 @@
 // #LAYOUT# *   BASIC_0 #TAKE-HIGH
 // #LAYOUT# *   *       #IGNORE
 
-// This has to go $E000 or above - routines below banks out the main BASIC ROM!
+// This has to go $E000 or above - routine below banks out the main BASIC ROM!
 
 //
 // Helper routine to copy string descriptor