From 5965930bd0f76261d5916c7019c08eb8f21e1b1b Mon Sep 17 00:00:00 2001
From: nmlgc <nmlgc@nmlgc.net>
Date: Sat, 7 Nov 2020 20:12:04 +0100
Subject: [PATCH] [Decompilation] [th03] .MRS: Persistent horizontal flipping

Another function consisting almost entirely of inline ASM. Still worth
it though, if only to save us from duplicating any declarations in ASM
land.

Part of P0126, funded by [Anonymous] and Blue Bolt.
---
 Makefile.mak         |  2 +-
 th03/formats/mrs.cpp | 51 ++++++++++++++++++++++++++++++++++++
 th03/formats/mrs.hpp |  3 +++
 th03/mrs.cpp         |  1 +
 th03_main.asm        | 61 +++-----------------------------------------
 5 files changed, 59 insertions(+), 59 deletions(-)
 create mode 100644 th03/mrs.cpp

diff --git a/Makefile.mak b/Makefile.mak
index 577433ca..9326a7d8 100644
--- a/Makefile.mak
+++ b/Makefile.mak
@@ -104,7 +104,7 @@ bin\th03\op.exe: th03\op_01.cpp bin\th03\op.obj bin\th03\inp_m_w.obj bin\th03\cd
 $**
 |
 
-bin\th03\main.exe: bin\th03\main.obj th03\main_01.cpp th03\sprite16.cpp
+bin\th03\main.exe: bin\th03\main.obj th03\main_01.cpp th03\mrs.cpp th03\sprite16.cpp
 	$(CC) $(CFLAGS) -ml -Z -DGAME=3 -nbin\th03\ -eMAIN.EXE @&&|
 $**
 |
diff --git a/th03/formats/mrs.cpp b/th03/formats/mrs.cpp
index 6312f5e5..4b472ee7 100644
--- a/th03/formats/mrs.cpp
+++ b/th03/formats/mrs.cpp
@@ -1,6 +1,9 @@
+#pragma codeseg SHARED
+
 #include "platform.h"
 #include "pc98.h"
 #include "planar.h"
+#include "th03/formats/hfliplut.h"
 #include "th03/formats/mrs.hpp"
 
 static const vram_byte_amount_t MRS_BYTE_W = (MRS_W / BYTE_DOTS);
@@ -17,3 +20,51 @@ struct mrs_t {
 };
 
 extern mrs_t far *mrs_images[MRS_SLOT_COUNT];
+
+// Points [reg_sgm]:[reg_off] to the alpha plane of the .MRS image in the
+// given [slot].
+#define mrs_slot_assign(reg_sgm, reg_off, slot) { \
+	_BX = slot; \
+	_BX <<= 2; \
+	__asm { l##reg_sgm reg_off, mrs_images[bx]; } \
+}
+
+void pascal mrs_hflip(int slot)
+{
+	_CX = sizeof(mrs_t);
+	mrs_slot_assign(es, di, slot);
+	reinterpret_cast<dots8_t near *>(_BX) = hflip_lut;
+
+	flip_dots_within_bytes: __asm {
+		mov 	al, es:[di];
+		xlat;
+		mov 	es:[di], al;
+		inc 	di;
+		loop	flip_dots_within_bytes;
+	}
+
+	_CX = (sizeof(mrs_t) / MRS_BYTE_W);
+	/* vram_byte_amount_t offset_y */ _BX = 0;
+
+	flip_bytes: {
+		// Assumes that the offset part of all image pointers is 0. Storing
+		// segment pointers in [mrs_images] would have been clearer in this
+		// case...
+		/* vram_byte_amount_t offset_left  */ _DI = 0;
+		/* vram_byte_amount_t offset_right */ _SI = (MRS_BYTE_W - 1);
+		do {
+			__asm {
+				mov al, es:[bx+di]
+				mov dl, es:[bx+si]
+				mov es:[bx+si], al
+				mov es:[bx+di], dl
+			}
+			_SI--;
+			_DI++;
+		} while(_DI <= ((MRS_BYTE_W / 2) - 1));
+		_BX += MRS_BYTE_W;
+		__asm { loop flip_bytes; }
+	}
+}
+
+#pragma codestring "\x90"
diff --git a/th03/formats/mrs.hpp b/th03/formats/mrs.hpp
index ef8ef6f5..ad9e19d4 100644
--- a/th03/formats/mrs.hpp
+++ b/th03/formats/mrs.hpp
@@ -6,4 +6,7 @@
 static const int MRS_SLOT_COUNT = 8;
 static const pixel_t MRS_W = 288;
 static const pixel_t MRS_H = 184;
+
+// Persistently flips the image in [slot] horizontally, using the [hflip_lut].
+void pascal mrs_hflip(int slot);
 /// ---------------------------------------------------------------------------
diff --git a/th03/mrs.cpp b/th03/mrs.cpp
new file mode 100644
index 00000000..54641495
--- /dev/null
+++ b/th03/mrs.cpp
@@ -0,0 +1 @@
+#include "th03/formats/mrs.cpp"
diff --git a/th03_main.asm b/th03_main.asm
index 5d596d33..c2670e35 100644
--- a/th03_main.asm
+++ b/th03_main.asm
@@ -1583,10 +1583,8 @@ sub_A4A1	proc near
 
 		push	bp
 		mov	bp, sp
-		push	1
-		call	sub_F0A6
-		push	3
-		call	sub_F0A6
+		call	@mrs_hflip$qi pascal, 1
+		call	@mrs_hflip$qi pascal, 3
 		call	respal_get_palettes
 		call	far ptr	palette_show
 		nopcall	sub_A378
@@ -9152,60 +9150,7 @@ sub_EFF4	endp
 
 ; ---------------------------------------------------------------------------
 		nop
-
-; =============== S U B	R O U T	I N E =======================================
-
-; Attributes: bp-based frame
-
-sub_F0A6	proc far
-
-arg_0		= word ptr  6
-
-		push	bp
-		mov	bp, sp
-
-loc_F0A9:
-		push	si
-		push	di
-		mov	cx, 8160h
-		mov	bx, [bp+arg_0]
-		shl	bx, 2
-		les	di, _mrs_images[bx]
-		mov	bx, offset _hflip_lut
-
-loc_F0BB:
-		mov	al, es:[di]
-		xlat
-		mov	es:[di], al
-		inc	di
-		loop	loc_F0BB
-		mov	cx, 398h
-		xor	bx, bx
-
-loc_F0CA:
-		xor	di, di
-		mov	si, 23h	; '#'
-
-loc_F0CF:
-		mov	al, es:[bx+di]
-		mov	dl, es:[bx+si]
-		mov	es:[bx+si], al
-		mov	es:[bx+di], dl
-		dec	si
-		inc	di
-		cmp	di, 11h
-		jbe	short loc_F0CF
-		add	bx, 24h	; '$'
-		loop	loc_F0CA
-		pop	di
-		pop	si
-		pop	bp
-		retf	2
-sub_F0A6	endp
-
-; ---------------------------------------------------------------------------
-		nop
-
+	extern @MRS_HFLIP$QI:proc
 	SPRITE16_SPRITES_COMMIT procdesc pascal far
 	SPRITE16_PUT procdesc pascal far \
 		left:word, screen_top:word, sprite_offset:word