optimizations in garbage collector

src/basic/engine_variables/helper_gc_misc_46K_50K.s

@@ -0,0 +1,57 @@
+// #LAYOUT# STD *       #TAKE-HIGH
+// #LAYOUT# *   BASIC_0 #TAKE-HIGH
+// #LAYOUT# *   *       #IGNORE
+
+// This has to go $E000 or above - routines below bank out the main BASIC ROM!
+
+#if CONFIG_MEMORY_MODEL_46K || CONFIG_MEMORY_MODEL_50K
+
+helper_gc_set_memmove_src:
+
+	// Unmap BASIC lower ROM
+
+	lda #$26
+	sta CPU_R6510
+
+	// Set memmove__src
+
+	lda (OLDTXT),y
+	sta memmove__src+0
+	iny
+	lda (OLDTXT),y
+	sta memmove__src+1
+
+	// Restore default memory mapping
+
+	jmp_8 helper_gc_misc_end
+
+helper_gc_increase_oldtxt:
+
+	// Unmap BASIC lower ROM
+
+	lda #$26
+	sta CPU_R6510
+
+	// Increase OLDTXT accordingly
+
+	lda (OLDTXT),y
+	clc
+	adc INDEX+0
+	sta (OLDTXT),y
+	iny
+	lda (OLDTXT),y
+	adc INDEX+1
+	sta (OLDTXT),y
+
+	// FALLTROUGH
+
+helper_gc_misc_end:
+
+	// Restore default memory mapping
+
+	lda #$27
+	sta CPU_R6510
+
+	rts
+
+#endif