From c81269eebe7528ca50d9a9d9175ddf99d7e871cb Mon Sep 17 00:00:00 2001
From: Patryk Obara <dreamer.tan@gmail.com>
Date: Wed, 18 Dec 2019 21:34:38 +0100
Subject: [PATCH] Remove extern global variable from bios_disk.h

This way interface of swapInDisks function is cleaner and we avoid a
warning when comparing (previously) signed swap position with an
unsigned array size or index.

Also, add some documentation to swapInDisks function.
---
 include/bios_disk.h      | 14 ++++++++++++--
 src/dos/dos_programs.cpp |  4 +---
 src/ints/bios_disk.cpp   | 15 ++++++++-------
 3 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/include/bios_disk.h b/include/bios_disk.h
index a13aa344..562b0dc6 100644
--- a/include/bios_disk.h
+++ b/include/bios_disk.h
@@ -84,12 +84,22 @@ void incrementFDD(void);
 extern std::array<std::shared_ptr<imageDisk>, MAX_DISK_IMAGES> imageDiskList;
 extern std::array<std::shared_ptr<imageDisk>, MAX_SWAPPABLE_DISKS> diskSwap;
 
-extern Bit32s swapPosition;
 extern Bit16u imgDTASeg; /* Real memory location of temporary DTA pointer for fat image disk access */
 extern RealPt imgDTAPtr; /* Real memory location of temporary DTA pointer for fat image disk access */
 extern DOS_DTA *imgDTA;
 
-void swapInDisks(void);
+/**
+ * Insert 2 boot disks starting at swap_position into the drives A and B.
+ *
+ * Selected disks are wrapped around, so swapping in the last boot disk
+ * will place the first disk into drive B.
+ *
+ * When there's only 1 disk, it will be placed into both A and B drives.
+ *
+ * When there's no boot disks loaded, this function has no effect.
+ */
+void swapInDisks(unsigned int swap_position);
+
 void swapInNextDisk(void);
 bool getSwapRequest(void);
 
diff --git a/src/dos/dos_programs.cpp b/src/dos/dos_programs.cpp
index 27e0c6b0..00399cea 100644
--- a/src/dos/dos_programs.cpp
+++ b/src/dos/dos_programs.cpp
@@ -676,9 +676,7 @@ public:
 			i++;
 		}
 
-		swapPosition = 0;
-
-		swapInDisks();
+		swapInDisks(0);
 
 		if (!imageDiskList[drive - 'A']) {
 			WriteOut(MSG_Get("PROGRAM_BOOT_UNABLE"), drive);
diff --git a/src/ints/bios_disk.cpp b/src/ints/bios_disk.cpp
index 4fb5c6aa..0c434e0e 100644
--- a/src/ints/bios_disk.cpp
+++ b/src/ints/bios_disk.cpp
@@ -59,7 +59,8 @@ void CMOS_SetRegister(Bitu regNr, Bit8u val); //For setting equipment word
 /* 2 floppys and 2 harddrives, max */
 std::array<std::shared_ptr<imageDisk>, MAX_DISK_IMAGES> imageDiskList;
 std::array<std::shared_ptr<imageDisk>, MAX_SWAPPABLE_DISKS> diskSwap;
-Bit32s swapPosition;
+
+unsigned int swapPosition;
 
 void updateDPT(void) {
 	Bit32u tmpheads, tmpcyl, tmpsect, tmpsize;
@@ -111,14 +112,14 @@ static size_t disk_array_prefix_size(const std::array<T, N> &images) {
 	return num;
 }
 
-void swapInDisks(void) {
+void swapInDisks(unsigned int swap_position) {
 	const size_t boot_disks_num = disk_array_prefix_size(diskSwap);
 	if (boot_disks_num == 0)
 		return;
 
-	assert(swapPosition < boot_disks_num);
-	const unsigned int pos_1 = swapPosition;
-	const unsigned int pos_2 = (swapPosition + 1) % boot_disks_num;
+	assert(swap_position < boot_disks_num);
+	const unsigned int pos_1 = swap_position;
+	const unsigned int pos_2 = (swap_position + 1) % boot_disks_num;
 
 	imageDiskList[0] = diskSwap[pos_1];
 	LOG_MSG("Loaded disk A from swaplist position %u - \"%s\"",
@@ -145,10 +146,10 @@ void swapInNextDisk(bool pressed) {
 		if (Drives[i]) Drives[i]->EmptyCache();
 	}
 	swapPosition++;
-	if(!diskSwap[swapPosition]) {
+	if (!diskSwap[swapPosition]) {
 		swapPosition = 0;
 	}
-	swapInDisks();
+	swapInDisks(swapPosition);
 	swapping_requested = true;
 }