From b2ca61030edf8c659e179a76a610b2b66063fa7f Mon Sep 17 00:00:00 2001
From: Peter Veenstra <qbix79@users.sourceforge.net>
Date: Wed, 8 Feb 2006 15:13:06 +0000
Subject: [PATCH] Fix ROM checksum. (was broken as setupvesa modifies the rom
 as well)

Imported-from: https://svn.code.sf.net/p/dosbox/code-0/dosbox/trunk@2476
---
 src/ints/int10.cpp        |  1 +
 src/ints/int10.h          |  1 +
 src/ints/int10_memory.cpp | 21 ++++++++++++++-------
 3 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/src/ints/int10.cpp b/src/ints/int10.cpp
index 8c66058d..53a4a013 100644
--- a/src/ints/int10.cpp
+++ b/src/ints/int10.cpp
@@ -546,5 +546,6 @@ void INT10_Init(Section* sec) {
 	INT10_SetupRomMemory();
 	INT10_Seg40Init();
 	INT10_SetupVESA();
+	INT10_SetupRomMemoryChecksum();//SetupVesa modifies the rom as well.
 	INT10_SetVideoMode(machine==MCH_HERC ? 0x7 : 0x3);
 };
diff --git a/src/ints/int10.h b/src/ints/int10.h
index aa195c1b..8ae53e17 100644
--- a/src/ints/int10.h
+++ b/src/ints/int10.h
@@ -201,6 +201,7 @@ Bit8u VESA_GetPalette(PhysPt data,Bitu index,Bitu count);
 
 /* Sup Groups */
 void INT10_SetupRomMemory(void);
+void INT10_SetupRomMemoryChecksum(void);
 void INT10_SetupVESA(void);
 
 /* EGA RIL */
diff --git a/src/ints/int10_memory.cpp b/src/ints/int10_memory.cpp
index 52f51a3d..abdedc69 100644
--- a/src/ints/int10_memory.cpp
+++ b/src/ints/int10_memory.cpp
@@ -72,6 +72,7 @@ void INT10_LoadFont(PhysPt font,bool reload,Bitu count,Bitu offset,Bitu map,Bitu
 	}
 }
 
+static Bitu checksumlocation = 0; //Same type as int10.rom.used
 void INT10_SetupRomMemory(void) {
 /* This should fill up certain structures inside the Video Bios Rom Area */
 	PhysPt rom_base=PhysMake(0xc000,0);
@@ -113,16 +114,22 @@ void INT10_SetupRomMemory(void) {
 	RealSetVec(0x1F,int10.rom.font_8_second);
 
 	if (machine == MCH_VGA) { //EGA/VGA. Just to be safe
-		/* Sum of all bytes in rom module 256 should be 0 */
-		Bit8u sum = 0;
-		for (i = 0;i < 32 * 1024;i++) //32 KB romsize
-			sum += phys_readb(rom_base + i); //OVERFLOW IS OKAY
-		sum = 256 - sum;
-		phys_writeb(rom_base+int10.rom.used++,sum);
+		//Reserve checksum location
+		checksumlocation = int10.rom.used++;
 	}
 };
 
-
+void INT10_SetupRomMemoryChecksum(void) {
+	if (machine == MCH_VGA) { //EGA/VGA. Just to be safe
+		/* Sum of all bytes in rom module 256 should be 0 */
+		Bit8u sum = 0;
+		PhysPt rom_base = PhysMake(0xc000,0);
+		for (Bitu i = 0;i < 32 * 1024;i++) //32 KB romsize
+			sum += phys_readb(rom_base + i); //OVERFLOW IS OKAY
+		sum = 256 - sum;
+		phys_writeb(rom_base + checksumlocation,sum);
+	}
+}
 
 
 Bit8u int10_font_08[256 * 8] = {