From 5fef7164a5edf42cf2d74089212be5316c937541 Mon Sep 17 00:00:00 2001
From: ripsaw8080 <ripsaw8080@users.sourceforge.net>
Date: Tue, 6 Jan 2015 17:48:07 +0000
Subject: [PATCH] Coalesce free memory blocks after resizing a block rather
 than before. Fixes some MicroProse games on the Tandy machine type. Also add
 error exits in case of a corrupt MCB chain instead of hanging in an infinite
 loop.

Imported-from: https://svn.code.sf.net/p/dosbox/code-0/dosbox/trunk@3882
---
 src/dos/dos_memory.cpp | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/dos/dos_memory.cpp b/src/dos/dos_memory.cpp
index 7a86a0ea..7ab32bdb 100644
--- a/src/dos/dos_memory.cpp
+++ b/src/dos/dos_memory.cpp
@@ -33,7 +33,8 @@ static void DOS_CompressMemory(void) {
 
 	while (mcb.GetType()!=0x5a) {
 		mcb_next.SetPt((Bit16u)(mcb_segment+mcb.GetSize()+1));
-		if ((mcb.GetPSPSeg()==0) && (mcb_next.GetPSPSeg()==0)) {
+		if (GCC_UNLIKELY((mcb_next.GetType()!=0x4d) && (mcb_next.GetType()!=0x5a))) E_Exit("Corrupt MCB chain");
+		if ((mcb.GetPSPSeg()==MCB_FREE) && (mcb_next.GetPSPSeg()==MCB_FREE)) {
 			mcb.SetSize(mcb.GetSize()+mcb_next.GetSize()+1);
 			mcb.SetType(mcb_next.GetType());
 		} else {
@@ -58,6 +59,7 @@ void DOS_FreeProcessMemory(Bit16u pspseg) {
 				mcb.SetType(0x4d);
 			} else break;
 		}
+		if (GCC_UNLIKELY(mcb.GetType()!=0x4d)) E_Exit("Corrupt MCB chain");
 		mcb_segment+=mcb.GetSize()+1;
 		mcb.SetPt(mcb_segment);
 	}
@@ -111,7 +113,7 @@ bool DOS_AllocateMemory(Bit16u * segment,Bit16u * blocks) {
 	Bit16u found_seg=0,found_seg_size=0;
 	for (;;) {
 		mcb.SetPt(mcb_segment);
-		if (mcb.GetPSPSeg()==0) {
+		if (mcb.GetPSPSeg()==MCB_FREE) {
 			/* Check for enough free memory in current block */
 			Bit16u block_size=mcb.GetSize();			
 			if (block_size<(*blocks)) {
@@ -225,12 +227,12 @@ bool DOS_ResizeMemory(Bit16u segment,Bit16u * blocks) {
 		return false;
 	}
 
-	DOS_CompressMemory();
 	Bit16u total=mcb.GetSize();
 	DOS_MCB	mcb_next(segment+total);
 	if (*blocks<=total) {
 		if (GCC_UNLIKELY(*blocks==total)) {
 			/* Nothing to do */
+			DOS_CompressMemory();
 			return true;
 		}
 		/* Shrinking MCB */
@@ -245,6 +247,7 @@ bool DOS_ResizeMemory(Bit16u segment,Bit16u * blocks) {
 		mcb_new_next.SetSize(total-*blocks-1);
 		mcb_new_next.SetPSPSeg(MCB_FREE);
 		mcb.SetPSPSeg(dos.psp());
+		DOS_CompressMemory();
 		return true;
 	}
 	/* MCB will grow, try to join with following MCB */
@@ -265,6 +268,7 @@ bool DOS_ResizeMemory(Bit16u segment,Bit16u * blocks) {
 		mcb_next.SetPSPSeg(MCB_FREE);
 		mcb.SetType(0x4d);
 		mcb.SetPSPSeg(dos.psp());
+		DOS_CompressMemory();
 		return true;
 	}
 
@@ -277,6 +281,7 @@ bool DOS_ResizeMemory(Bit16u segment,Bit16u * blocks) {
 	}
 	mcb.SetSize(total);
 	mcb.SetPSPSeg(dos.psp());
+	DOS_CompressMemory();
 	if (*blocks==total) return true;	/* block fit exactly */
 
 	*blocks=total;	/* return maximum */