variable support cleanup

src/basic/engine_editor/shift_txt_up.s

@@ -0,0 +1,58 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+
+//
+// Shift the BASIC program up to make space for a new line
+//
+
+
+shift_txt_up:
+	
+	// Last byte of source is VARTAB-1
+
+#if !HAS_OPCODES_65CE02
+
+	sec
+	lda VARTAB+0
+	sbc #$01
+	sta memmove__src+0
+	lda VARTAB+1
+	sbc #$00
+	sta memmove__src+1	
+
+#else // HAS_OPCODES_65CE02
+
+	lda VARTAB+0
+	sta memmove__src+0
+	lda VARTAB+1
+	sta memmove__src+1
+	dew memmove__src
+
+#endif
+
+	// Last byte of destination is memmove__src + .X
+
+	clc
+	txa
+
+	adc memmove__src+0
+	sta memmove__dst+0
+	lda memmove__src+1
+	adc #$00
+	sta memmove__dst+1
+
+	// Size is distance from OLDTXT to the end of BASIC text (VARTAB)
+
+	lda VARTAB+0
+	sec
+	sbc OLDTXT+0
+	sta memmove__size+0
+	lda VARTAB+1
+	sbc OLDTXT+1
+	sta memmove__size+1
+
+	// Perform the copy
+
+	jmp shift_mem_up