From 580b7961a5e1576edecafbbf064bf8776d851461 Mon Sep 17 00:00:00 2001
From: Paul Gardner-Stephen <paul@servalproject.org>
Date: Sun, 28 Apr 2019 00:28:38 +0930
Subject: [PATCH] more work on inserting and deleting BASIC lines.

---
 c64/basic/basic_find_line.s         |  8 ++--
 c64/basic/basic_shift_mem_up.s      | 73 +++++++++++++++++++++++++++++
 c64/basic/peek_pointer_null_check.s | 18 +++++++
 c64/basic/under_rom_routines.s      | 37 ---------------
 4 files changed, 94 insertions(+), 42 deletions(-)
 create mode 100644 c64/basic/basic_shift_mem_up.s
 create mode 100644 c64/basic/peek_pointer_null_check.s

diff --git a/c64/basic/basic_find_line.s b/c64/basic/basic_find_line.s
index a3d96322..bc3571d5 100644
--- a/c64/basic/basic_find_line.s
+++ b/c64/basic/basic_find_line.s
@@ -29,11 +29,9 @@ not_this_line:
 	;; Not this line, so advance to next line
 	ldy #0
 	ldx #<basic_current_line_ptr
-	jsr peek_under_roms
-	bne more_lines_exist
-	iny
-	jsr peek_under_roms
-	bne more_lines_exist
+	jsr peek_pointer_null_check
+	bcs more_lines_exist
+
 	;; no more lines exist, return failure
 line_num_too_high:	
 	sec
diff --git a/c64/basic/basic_shift_mem_up.s b/c64/basic/basic_shift_mem_up.s
new file mode 100644
index 00000000..5f12ef69
--- /dev/null
+++ b/c64/basic/basic_shift_mem_up.s
@@ -0,0 +1,73 @@
+
+
+basic_shift_mem_up_and_relink:
+	;; Shift memory up from basic_current_line_ptr
+	;; X bytes.
+
+	;; Work out end point of destination
+	txa
+	clc
+	adc basic_end_of_text_ptr+0
+	sta memmove_dst+0
+	lda basic_end_of_text_ptr+1
+	adc #0
+	sta memmove_dst+1
+	;; End point of source is just current end of BASIC text
+	lda basic_end_of_text_ptr+0
+	sta memmove_src
+	lda basic_end_of_text_ptr+1
+	sta memmove_src+1
+
+	;; Work out size of region to copy
+	lda basic_end_of_text_ptr+1
+	sec
+	sbc basic_current_line_ptr+1
+	sta memmove_size+1
+	lda basic_end_of_text_ptr+0
+	sbc #0
+	sta memmove_size+0
+
+	;; To make life simple for the copy routine that lives in RAM,
+	;; we have to adjust the end pointers down one page and set Y to the low
+	;; byte of the copy size.
+	tay
+	dec memmove_src+1
+	dec memmove_dst+1
+
+	;; Do the copy
+	jsr shift_mem_up
+	
+	;; Now fix the pointer for the BASIC lines
+
+	;; First, we need to point the current BASIC line
+	;; pointer to the previously present lines
+	stx tokenise_work3
+relink_up_next_line:	
+	ldx tokenise_work3
+	clc
+	adc basic_current_line_ptr+0
+	sta memmove_src+0
+	lda basic_current_line_ptr+1
+	adc #0
+	sta memmove_src+1
+	ldx #0
+	ldy #<basic_current_line_ptr
+	lda memmove_src+0
+	jsr poke_under_roms
+	inx
+	lda memmove_src+1
+	jsr poke_under_roms
+
+relink_up_loop:	
+	;; Now advance pointer to the next line,
+	lda memmove_src+0
+	sta basic_current_line_ptr+0
+	lda memmove_src+1
+	sta basic_current_line_ptr+1
+
+	;; Have we run out of lines to patch?
+	ldx #<basic_current_line_ptr
+	jsr peek_pointer_null_check
+	bcs relink_up_next_line
+
+	rts
diff --git a/c64/basic/peek_pointer_null_check.s b/c64/basic/peek_pointer_null_check.s
new file mode 100644
index 00000000..a476ae53
--- /dev/null
+++ b/c64/basic/peek_pointer_null_check.s
@@ -0,0 +1,18 @@
+	;; Return C=1 if a pointer in BASIC memory space is NULL, else C=0
+	;; X = ZP pointer to check
+
+peek_pointer_null_check:
+	ldy #$00
+	jsr peek_under_roms
+	bne ptr_not_null
+	iny
+	jsr peek_under_roms
+	bne ptr_not_null
+
+	;; Pointer is NULL
+	clc
+	rts
+ptr_not_null:
+	sec
+	rts
+	
diff --git a/c64/basic/under_rom_routines.s b/c64/basic/under_rom_routines.s
index 06ac764b..e5f45c10 100644
--- a/c64/basic/under_rom_routines.s
+++ b/c64/basic/under_rom_routines.s
@@ -21,43 +21,6 @@ install_ram_routines:
 
 	rts
 
-basic_shift_mem_up_and_relink:
-	;; Shift memory up from basic_current_line_ptr
-	;; X bytes.
-
-	;; Work out end point of destination
-	txa
-	clc
-	adc basic_end_of_text_ptr+0
-	sta memmove_dst+0
-	lda basic_end_of_text_ptr+1
-	adc #0
-	sta memmove_dst+1
-	;; End point of source is just current end of BASIC text
-	lda basic_end_of_text_ptr+0
-	sta memmove_src
-	lda basic_end_of_text_ptr+1
-	sta memmove_src+1
-
-	;; Work out size of region to copy
-	lda basic_end_of_text_ptr+1
-	sec
-	sbc basic_current_line_ptr+1
-	sta memmove_size+1
-	lda basic_end_of_text_ptr+0
-	sbc #0
-	sta memmove_size+0
-
-	;; To make life simple for the copy routine that lives in RAM,
-	;; we have to adjust the end pointers down one page and set Y to the low
-	;; byte of the copy size.
-	tay
-	dec memmove_src+1
-	dec memmove_dst+1
-
-	;; Do the copy
-	jmp shift_mem_up
-	
 ram_routines_start:	
 
 tiny_nmi_handler_routine: