some more size/speed optimizations

src/basic/engine_runtime/execute_line_statements.s

@@ -189,9 +189,8 @@ execute_line:
 
 	// Check if pointer is null, if so, we are at the end of the program
 
-	ldy #0
-	jsr peek_line_pointer_null_check
-	bcc_16 shell_main_loop             // branch if end of program reached
+	jsr is_line_pointer_null
+	beq_16 shell_main_loop             // branch if end of program reached
 
 	// Skip pointer and line number to get address of first statement
 

src/basic/engine_runtime/is_line_pointer_null_38K_60K.s

@@ -0,0 +1,37 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+// Return pointer in BASIC memory space status in Z flag
+
+
+#if CONFIG_MEMORY_MODEL_38K || CONFIG_MEMORY_MODEL_60K
+
+is_line_pointer_null:
+
+	// Check the pointer
+
+	ldy #$01                 // for non-NULL pointer, high byte is almost certainly not NULL
+
+#if CONFIG_MEMORY_MODEL_60K
+	ldx #<OLDTXT+0
+	jsr peek_under_roms
+	cmp #$00
+#else // CONFIG_MEMORY_MODEL_38K
+	lda (OLDTXT),y
+#endif
+
+	bne !+
+	dey
+
+#if CONFIG_MEMORY_MODEL_60K
+	jsr peek_under_roms
+	cmp #$00
+#else // CONFIG_MEMORY_MODEL_38K
+	lda (OLDTXT),y
+#endif
+
+!:
+	rts
+
+#endif

src/basic/engine_runtime/is_line_pointer_null_46K_50K.s

@@ -0,0 +1,37 @@
+// #LAYOUT# STD *       #TAKE-HIGH
+// #LAYOUT# *   BASIC_0 #TAKE-HIGH
+// #LAYOUT# *   *       #IGNORE
+
+// This has to go $E000 or above - routine below banks out the main BASIC ROM!
+
+// Return pointer in BASIC memory space status in Z flag
+
+
+#if CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+
+is_line_pointer_null:
+
+	// Unmap BASIC lower ROM
+
+	lda #$26
+	sta CPU_R6510
+
+	// Check the pointer
+
+	ldy #$01                 // for non-NULL pointer, high byte is almost certainly not NULL
+	lda (OLDTXT),y
+	bne !+                   // branch if pointer not NULL
+	
+	dey
+	lda (OLDTXT),y
+!:
+
+	// Restore memory mapping and quit
+
+	php
+	lda #$27
+	sta CPU_R6510
+	plp
+	rts
+
+#endif