Add multi-file disk image support.

MetaImgFile is a replacement for ImgFile.
It allows a virtual hard disk to be comprised of multiple parts of multiple files.
Each part is a called a chunk.
A chunk can be part of a file or can be bytes in RAM.

MetaImgFile::Open does the work of interpreting a disk image file. Currently, it supports raw disk images and Disk Copy 4.2 disk images.

If a disk image is a single partition with no partition map or a floppy disk image and is formatted with a known file system, then an Apple Partition Map is created in RAM.
Known file systems are MFS, HFS, and HFS+. The file system determines the partition type.

MetaImgFile::Open can append partitions from additional disk image files but only if all disk image files would create an Apple Partition Map virtual hard disk.

You can add as many partitions as you like up to 2 TB. Beyond that would require doubling the disk block size which might not be interpreted correctly in some cases.
Classic macOS seems to be limited to 16 or 18 partitions.

Author: joevt

thirdparty/Apple/AppleDiskPartitions.h

@@ -0,0 +1,130 @@
+/*
+     File:       AppleDiskPartitions.h
+ 
+     Contains:   The Apple disk partition scheme as defined in Inside Macintosh: Volume V.
+ 
+     Version:    Technology: Mac OS 9
+                 Release:    Universal Interfaces 3.4.2
+ 
+     Copyright:  © 2000-2002 by Apple Computer, Inc., all rights reserved
+ 
+     Bugs?:      For bug reports, consult the following page on
+                 the World Wide Web:
+ 
+                     http://developer.apple.com/bugreporter/
+ 
+*/
+#ifndef __APPLEDISKPARTITIONS__
+#define __APPLEDISKPARTITIONS__
+
+#include <thirdparty/Apple/HFSVolumes.h>
+#include <cinttypes>
+
+#pragma pack(push, 1)
+
+/* Block 0 Definitions */
+enum {
+  sbSIGWord                     = 0x4552, /* signature word for Block 0 ('ER') */
+  sbMac                         = 1     /* system type for Mac */
+};
+
+/* Partition Map Signatures */
+enum {
+  pMapSIG                       = 0x504D, /* partition map signature ('PM') */
+  pdSigWord                     = 0x5453, /* partition map signature ('TS') */
+  oldPMSigWord                  = pdSigWord,
+  newPMSigWord                  = pMapSIG
+};
+
+
+/* Driver Descriptor Map */
+struct Block0 {
+  uint16_t              sbSig;                  /* 00 unique value for SCSI block 0 */
+  uint16_t              sbBlkSize;              /* 02 block size of device */
+  uint32_t              sbBlkCount;             /* 04 number of blocks on device */
+  uint16_t              sbDevType;              /* 08 device type */
+  uint16_t              sbDevId;                /* 0A device id */
+  uint32_t              sbData;                 /* 0C not used */
+  uint16_t              sbDrvrCount;            /* 10 driver descriptor count */
+  uint32_t              ddBlock;                /* 12 1st driver's starting block */
+  uint16_t              ddSize;                 /* 16 size of 1st driver (512-byte blks) */
+  uint16_t              ddType;                 /* 18 system type (1 for Mac+) */
+  uint16_t              ddPad[243];             /* 1A ARRAY[0..242] OF INTEGER; not used */
+};
+
+typedef struct Block0                   Block0;
+
+static_assert(sizeof(Block0) == 0x200);
+
+/* Driver descriptor */
+struct DDMap {
+  uint32_t              ddBlock;                /* 1st driver's starting block */
+  uint16_t              ddSize;                 /* size of 1st driver (512-byte blks) */
+  uint16_t              ddType;                 /* system type (1 for Mac+) */
+};
+typedef struct DDMap                    DDMap;
+/* Constants for the ddType field of the DDMap structure. */
+enum {
+  kDriverTypeMacSCSI            = 0x0001,
+  kDriverTypeMacATA             = 0x0701,
+  kDriverTypeMacSCSIChained     = 0xFFFF,
+  kDriverTypeMacATAChained      = 0xF8FF
+};
+
+/* Partition Map Entry */
+struct Partition {
+  uint16_t              pmSig;                  /*     0 unique value for map entry blk */
+  uint16_t              pmSigPad;               /*     2 currently unused */
+  uint32_t              pmMapBlkCnt;            /*     4 # of blks in partition map */
+  uint32_t              pmPyPartStart;          /*     8 physical start blk of partition */
+  uint32_t              pmPartBlkCnt;           /*     C # of blks in this partition */
+  uint8_t               pmPartName[32];         /*  0x10 ASCII partition name */
+  uint8_t               pmParType[32];          /*  0x30 ASCII partition type */
+  uint32_t              pmLgDataStart;          /*  0x50 log. # of partition's 1st data blk */
+  uint32_t              pmDataCnt;              /*  0x54 # of blks in partition's data area */
+  uint32_t              pmPartStatus;           /*  0x58 bit field for partition status */
+  uint32_t              pmLgBootStart;          /*  0x5C log. blk of partition's boot code */
+  uint32_t              pmBootSize;             /*  0x60 number of bytes in boot code */
+  uint32_t              pmBootAddr;             /*  0x64 memory load address of boot code */
+  uint32_t              pmBootAddr2;            /*  0x68 currently unused */
+  uint32_t              pmBootEntry;            /*  0x6C entry point of boot code */
+  uint32_t              pmBootEntry2;           /*  0x70 currently unused */
+  uint32_t              pmBootCksum;            /*  0x74 checksum of boot code */
+  uint8_t               pmProcessor[16];        /*  0x78 ASCII for the processor type */
+  uint16_t              pmPad[188];             /*  0x88 ARRAY[0..187] OF INTEGER; not used */
+};                                              /* 0x200 */
+typedef struct Partition                Partition;
+
+/* Flags for the pmPartStatus field of the Partition data structure. */
+enum {
+  kPartitionAUXIsValid          = 0x00000001,
+  kPartitionAUXIsAllocated      = 0x00000002,
+  kPartitionAUXIsInUse          = 0x00000004,
+  kPartitionAUXIsBootValid      = 0x00000008,
+  kPartitionAUXIsReadable       = 0x00000010,
+  kPartitionAUXIsWriteable      = 0x00000020,
+  kPartitionAUXIsBootCodePositionIndependent = 0x00000040,
+  kPartitionIsWriteable         = 0x00000020,
+  kPartitionIsMountedAtStartup  = 0x40000000,
+  kPartitionIsStartup           = (long)0x80000000,
+  kPartitionIsChainCompatible   = 0x00000100,
+  kPartitionIsRealDeviceDriver  = 0x00000200,
+  kPartitionCanChainToNext      = 0x00000400
+};
+
+
+
+
+/* Well known driver signatures, stored in the first four byte of pmPad. */
+enum {
+  kPatchDriverSignature         = FOUR_CHAR_CODE('ptDR'), /* SCSI and ATA[PI] patch driver    */
+  kSCSIDriverSignature          = 0x00010600, /* SCSI  hard disk driver           */
+  kATADriverSignature           = FOUR_CHAR_CODE('wiki'), /* ATA   hard disk driver           */
+  kSCSICDDriverSignature        = FOUR_CHAR_CODE('CDvr'), /* SCSI  CD-ROM    driver           */
+  kATAPIDriverSignature         = FOUR_CHAR_CODE('ATPI'), /* ATAPI CD-ROM    driver           */
+  kDriveSetupHFSSignature       = FOUR_CHAR_CODE('DSU1') /* Drive Setup HFS partition        */
+};
+
+#pragma pack(pop)
+
+#endif /* __APPLEDISKPARTITIONS__ */