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#                                     Pcompress File Format.                                              #
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Broadly a compressed file consists of a header followed by one or more metadata members which is turn is
followed by one or more compressed chunk data members.

Apart from a standard chunk header, each compressed chunk has an internal format with various metadata
headers of the compression and deduplication algorithms used.

===========================================
File Header
===========================================
8 Bytes - Compression algorithm name
2 Bytes - File format version
2 Bytes - Flags
	
 *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *
 15  14  13  12  11  10  9   8   7   6   5   4   3   2   1   0
                     |       |           |   |       |   |   |
                     |       |           |   |       |   |   `- Simple buffer-level Deduplication on/off
                     '-------'           |   |       |   `----- Fixed Block Deduplication on/off
                         |               |   |       |          Both bits set indicate Global Deduplication.
                         |               |   |       |
                         |               |   |       `--------- Solid archive. Entire file compressed in a
                         |               |   |                  single buffer.
                         |               |   |
                         |               |   `----------------- AES Crypto
                         |               `--------------------- Salsa20 Crypto
                         |
                         `------------------------------------- Indicate which data verification checksum
                                                                was used.


8 Bytes - Indicated per-thread buffer size
4 Bytes - Compression level

If Encryption Used
-------------------------------------------
4 Bytes - Salt Length
X Bytes - Actual Salt bytes
X Bytes - Nonce: 8 Bytes for AES and 24 Bytes for Salsa20
4 Bytes - Key Length
===========================================
Header Checksum
===========================================
X Bytes - 4 Byte CRC32 without encryption
          Header HMAC if encryption enabled. Size of HMAC depends on selected data verification hash.
===========================================
Chunk Header
Each chunk is a single compressed buffer
===========================================
8 Bytes - Compressed Length
X Bytes - Chunk data verification hash (upto 64 bytes) of the original uncompressed and unencrypted
          data.
X Bytes - Chunk Header CRC32 for normal compression
          Full chunk HMAC, including header, when encrypting. Computation is in this order:
          Compression -> Encryption -> HMAC.
1 Byte  - Chunk Flags

   *  *  *  *  *  *  *  *
   7  6  5  4  3  2  1  0
   |  |     |     |  |  |
   |  '-----'     |  |  `- 0 - Uncompressed
   |     |        |  |     1 - Compressed
   |     |        |  |   
   |     |        |  `---- 1 - Chunk was Deduped
   |     |        `------- 1 - Chunk was pre-compressed
   |     |
   |     |                 1 - Lzma (Adaptive Mode)
   |     |                 2 - Bzip2 (Adaptive Mode)
   |     `---------------- 3 - PPMD (Adaptive Mode)
   |                       4 - Libbsc (Adaptive Mode)
   |                       5 - LZ4 (Adaptive Mode)
   |
   `---------------------- 1 - Chunk size flag (if original chunk is of variable length)

X Bytes - Compressed chunk data

Original uncompressed chunk size can be less than indicated per-thread buffer size. In that
case chunk size bit is set in the flags (as above) and size value is appended after the
compressed chunk data.
-------------------------------------------
8 Bytes - Original uncompressed chunk size
===========================================
File Trailer
===========================================
8 Bytes - Zero bytes indicating zero compressed length
          and end of file.