Disassemble the decompression routine

3 files changed, 90 insertions, 0 deletions

diff --git a/shim.sym b/shim.sym
index c7960a2..57a56fd 100644
--- a/shim.sym
+++ b/shim.sym
@@ -59,6 +59,10 @@
 
 3c:4377 function_3c_4377
 
+6c:7eec compressed_tilemap_6c_7eec
+
+75:7d35 compressed_gfx_75_7d35
+
 7b:41e0 gfx_blank_char
 
 00:a03e s_a03e
@@ -88,6 +92,7 @@
 00:c318 w_farcall_target_high
 00:c31e w_bank_temp ; db
 
+00:c300 w_c300
 00:c301 w_c301
 00:c314 w_c314
 00:c316 w_c316
diff --git a/source/bank_00.asm b/source/bank_00.asm
index ae4a7cb..21d3160 100644
--- a/source/bank_00.asm
+++ b/source/bank_00.asm
@@ -1472,6 +1472,71 @@ text_draw_char:
     ld a, e
     ret
 
+SECTION "decompress", ROM0[$20cf]
+decompress::
+; Parameters:
+; hl - source
+; de - dest
+; bc - length (not the actual source or dest length)
+    ld [w_bank_temp], a
+    ld a, [w_bank_rom]
+    push af
+    ld a, [w_bank_temp]
+    ld [w_bank_rom], a
+    ld [rROMB0], a
+
+    xor a
+    ld [w_c300], a
+
+.main_loop
+    push bc
+    ld a, [hl+]
+    bit 7, a
+    jr nz, .alternating
+
+; uses the next a + 1 bytes of compressed data
+; to output a + 1 bytes of decompressed data
+    inc a
+    ld c, a
+    ld a, [w_c300]
+.seq_loop
+    xor [hl]
+    ld [de], a
+    inc hl
+    inc de
+    dec c
+    jr nz, .seq_loop
+    ld [w_c300], a
+    jr .next
+
+; uses the next one byte of compressed data
+; to output a - $7e bytes of decompressed data,
+; alternating between two different values
+.alternating
+    sub $7e
+    ld c, a
+    ld a, [w_c300]
+.alt_loop
+    xor [hl]
+    ld [de], a
+    inc de
+    dec c
+    jr nz, .alt_loop
+    ld [w_c300], a
+    inc hl
+
+.next
+    pop bc
+    dec bc
+    ld a, c
+    or b
+    jr nz, .main_loop
+
+    pop af
+    ld [w_bank_rom], a
+    ld [rROMB0], a
+    ret
+
 SECTION "function_00_24b7", ROM0[$24b7]
 function_00_24b7::
     xor a
diff --git a/source/bank_28.asm b/source/bank_28.asm
new file mode 100644
index 0000000..d798744
--- /dev/null
+++ b/source/bank_28.asm
@@ -0,0 +1,20 @@
+INCLUDE "hardware.inc"
+INCLUDE "macros.inc"
+
+SECTION "function_28_426a", ROMX[$426a], BANK[$28]
+
+function_28_426a::
+    ld a, $01
+    ld [w_d6b5], a
+    ld a, BANK(compressed_gfx_75_7d35)
+    ld hl, compressed_gfx_75_7d35
+    ld de, _VRAM8800
+    ld bc, 182
+    call decompress
+    ld a, BANK(compressed_tilemap_6c_7eec)
+    ld hl, compressed_tilemap_6c_7eec
+    ld de, _SCRN0
+    ld bc, 82
+    call decompress
+    call function_00_1085
+    ; TBC