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+7z Format description (18.06)
+----------------------------
+
+This file contains description of 7z archive format. 
+7z archive can contain files compressed with any method.
+See "Methods.txt" for description for defined compressing methods.
+
+
+Format structure Overview
+-------------------------
+
+Some fields can be optional.
+
+Archive structure
+~~~~~~~~~~~~~~~~~  
+SignatureHeader
+[PackedStreams]
+[PackedStreamsForHeaders]
+[
+  Header 
+  or 
+  {
+    Packed Header
+    HeaderInfo
+  }
+]
+
+
+
+Header structure
+~~~~~~~~~~~~~~~~  
+{
+  ArchiveProperties
+  AdditionalStreams
+  {
+    PackInfo
+    {
+      PackPos
+      NumPackStreams
+      Sizes[NumPackStreams]
+      CRCs[NumPackStreams]
+    }
+    CodersInfo
+    {
+      NumFolders
+      Folders[NumFolders]
+      {
+        NumCoders
+        CodersInfo[NumCoders]
+        {
+          ID
+          NumInStreams;
+          NumOutStreams;
+          PropertiesSize
+          Properties[PropertiesSize]
+        }
+        NumBindPairs
+        BindPairsInfo[NumBindPairs]
+        {
+          InIndex;
+          OutIndex;
+        }
+        PackedIndices
+      }
+      UnPackSize[Folders][Folders.NumOutstreams]
+      CRCs[NumFolders]
+    }
+    SubStreamsInfo
+    {
+      NumUnPackStreamsInFolders[NumFolders];
+      UnPackSizes[]
+      CRCs[]
+    }
+  }
+  MainStreamsInfo
+  {
+    (Same as in AdditionalStreams)
+  }
+  FilesInfo
+  {
+    NumFiles
+    Properties[]
+    {
+      ID
+      Size
+      Data
+    }
+  }
+}
+
+HeaderInfo structure
+~~~~~~~~~~~~~~~~~~~~
+{
+  (Same as in AdditionalStreams)
+}
+
+
+
+Notes about Notation and encoding
+---------------------------------
+
+7z uses little endian encoding.
+
+7z archive format has optional headers that are marked as
+[]
+Header
+[]
+
+REAL_UINT64 means real UINT64.
+
+UINT64 means real UINT64 encoded with the following scheme:
+
+  Size of encoding sequence depends from first byte:
+  First_Byte  Extra_Bytes        Value
+  (binary)   
+  0xxxxxxx               : ( xxxxxxx           )
+  10xxxxxx    BYTE y[1]  : (  xxxxxx << (8 * 1)) + y
+  110xxxxx    BYTE y[2]  : (   xxxxx << (8 * 2)) + y
+  ...
+  1111110x    BYTE y[6]  : (       x << (8 * 6)) + y
+  11111110    BYTE y[7]  :                         y
+  11111111    BYTE y[8]  :                         y
+
+
+
+Property IDs
+------------
+
+0x00 = kEnd
+
+0x01 = kHeader
+
+0x02 = kArchiveProperties
+    
+0x03 = kAdditionalStreamsInfo
+0x04 = kMainStreamsInfo
+0x05 = kFilesInfo
+    
+0x06 = kPackInfo
+0x07 = kUnPackInfo
+0x08 = kSubStreamsInfo
+
+0x09 = kSize
+0x0A = kCRC
+
+0x0B = kFolder
+
+0x0C = kCodersUnPackSize
+0x0D = kNumUnPackStream
+
+0x0E = kEmptyStream
+0x0F = kEmptyFile
+0x10 = kAnti
+
+0x11 = kName
+0x12 = kCTime
+0x13 = kATime
+0x14 = kMTime
+0x15 = kWinAttributes
+0x16 = kComment
+
+0x17 = kEncodedHeader
+
+0x18 = kStartPos
+0x19 = kDummy
+
+
+7z format headers
+-----------------
+
+SignatureHeader
+~~~~~~~~~~~~~~~
+  BYTE kSignature[6] = {'7', 'z', 0xBC, 0xAF, 0x27, 0x1C};
+
+  ArchiveVersion
+  {
+    BYTE Major;   // now = 0
+    BYTE Minor;   // now = 4
+  };
+
+  UINT32 StartHeaderCRC;
+
+  StartHeader
+  {
+    REAL_UINT64 NextHeaderOffset
+    REAL_UINT64 NextHeaderSize
+    UINT32 NextHeaderCRC
+  }
+
+
+...........................
+
+
+ArchiveProperties
+~~~~~~~~~~~~~~~~~
+BYTE NID::kArchiveProperties (0x02)
+for (;;)
+{
+  BYTE PropertyType;
+  if (aType == 0)
+    break;
+  UINT64 PropertySize;
+  BYTE PropertyData[PropertySize];
+}
+
+
+Digests (NumStreams)
+~~~~~~~~~~~~~~~~~~~~~
+  BYTE AllAreDefined
+  if (AllAreDefined == 0)
+  {
+    for(NumStreams)
+      BIT Defined
+  }
+  UINT32 CRCs[NumDefined]
+
+
+PackInfo
+~~~~~~~~~~~~
+  BYTE NID::kPackInfo  (0x06)
+  UINT64 PackPos
+  UINT64 NumPackStreams
+
+  []
+  BYTE NID::kSize    (0x09)
+  UINT64 PackSizes[NumPackStreams]
+  []
+
+  []
+  BYTE NID::kCRC      (0x0A)
+  PackStreamDigests[NumPackStreams]
+  []
+
+  BYTE NID::kEnd
+
+
+Folder
+~~~~~~
+  UINT64 NumCoders;
+  for (NumCoders)
+  {
+    BYTE 
+    {
+      0:3 CodecIdSize
+      4:  Is Complex Coder
+      5:  There Are Attributes
+      6:  Reserved
+      7:  There are more alternative methods. (Not used anymore, must be 0).
+    } 
+    BYTE CodecId[CodecIdSize]
+    if (Is Complex Coder)
+    {
+      UINT64 NumInStreams;
+      UINT64 NumOutStreams;
+    }
+    if (There Are Attributes)
+    {
+      UINT64 PropertiesSize
+      BYTE Properties[PropertiesSize]
+    }
+  }
+    
+  NumBindPairs = NumOutStreamsTotal - 1;
+
+  for (NumBindPairs)
+  {
+    UINT64 InIndex;
+    UINT64 OutIndex;
+  }
+
+  NumPackedStreams = NumInStreamsTotal - NumBindPairs;
+  if (NumPackedStreams > 1)
+    for(NumPackedStreams)
+    {
+      UINT64 Index;
+    };
+
+
+
+
+Coders Info
+~~~~~~~~~~~
+
+  BYTE NID::kUnPackInfo  (0x07)
+
+
+  BYTE NID::kFolder  (0x0B)
+  UINT64 NumFolders
+  BYTE External
+  switch(External)
+  {
+    case 0:
+      Folders[NumFolders]
+    case 1:
+      UINT64 DataStreamIndex
+  }
+
+
+  BYTE ID::kCodersUnPackSize  (0x0C)
+  for(Folders)
+    for(Folder.NumOutStreams)
+     UINT64 UnPackSize;
+
+
+  []
+  BYTE NID::kCRC   (0x0A)
+  UnPackDigests[NumFolders]
+  []
+
+  
+
+  BYTE NID::kEnd
+
+
+
+SubStreams Info
+~~~~~~~~~~~~~~
+  BYTE NID::kSubStreamsInfo; (0x08)
+
+  []
+  BYTE NID::kNumUnPackStream; (0x0D)
+  UINT64 NumUnPackStreamsInFolders[NumFolders];
+  []
+
+
+  []
+  BYTE NID::kSize  (0x09)
+  UINT64 UnPackSizes[]
+  []
+
+
+  []
+  BYTE NID::kCRC  (0x0A)
+  Digests[Number of streams with unknown CRC]
+  []
+
+  
+  BYTE NID::kEnd
+
+
+Streams Info
+~~~~~~~~~~~~
+
+  []
+  PackInfo
+  []
+
+
+  []
+  CodersInfo
+  []
+
+
+  []
+  SubStreamsInfo
+  []
+
+  BYTE NID::kEnd
+
+
+FilesInfo
+~~~~~~~~~
+  BYTE NID::kFilesInfo;  (0x05)
+  UINT64 NumFiles
+
+  for (;;)
+  {
+    BYTE PropertyType;
+    if (aType == 0)
+      break;
+
+    UINT64 Size;
+
+    switch(PropertyType)
+    {
+      kEmptyStream:   (0x0E)
+        for(NumFiles)
+          BIT IsEmptyStream
+
+      kEmptyFile:     (0x0F)
+        for(EmptyStreams)
+          BIT IsEmptyFile
+
+      kAnti:          (0x10)
+        for(EmptyStreams)
+          BIT IsAntiFile
+      
+      case kCTime: (0x12)
+      case kATime: (0x13)
+      case kMTime: (0x14)
+        BYTE AllAreDefined
+        if (AllAreDefined == 0)
+        {
+          for(NumFiles)
+            BIT TimeDefined
+        }
+        BYTE External;
+        if(External != 0)
+          UINT64 DataIndex
+        []
+        for(Definded Items)
+          REAL_UINT64 Time
+        []
+      
+      kNames:     (0x11)
+        BYTE External;
+        if(External != 0)
+          UINT64 DataIndex
+        []
+        for(Files)
+        {
+          wchar_t Names[NameSize];
+          wchar_t 0;
+        }
+        []
+
+      kAttributes:  (0x15)
+        BYTE AllAreDefined
+        if (AllAreDefined == 0)
+        {
+          for(NumFiles)
+            BIT AttributesAreDefined
+        }
+        BYTE External;
+        if(External != 0)
+          UINT64 DataIndex
+        []
+        for(Definded Attributes)
+          UINT32 Attributes
+        []
+    }
+  }
+
+
+Header
+~~~~~~
+  BYTE NID::kHeader (0x01)
+
+  []
+  ArchiveProperties
+  []
+
+  []
+  BYTE NID::kAdditionalStreamsInfo; (0x03)
+  StreamsInfo
+  []
+
+  []
+  BYTE NID::kMainStreamsInfo;    (0x04)
+  StreamsInfo
+  []
+
+  []
+  FilesInfo
+  []
+
+  BYTE NID::kEnd
+
+
+HeaderInfo
+~~~~~~~~~~
+  []
+  BYTE NID::kEncodedHeader; (0x17)
+  StreamsInfo for Encoded Header
+  []
+
+
+---
+End of document