File: OVERVIEW

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ossp-uuid 1.6.2-1.5
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   _        ___  ____ ____  ____                _     _
  |_|_ _   / _ \/ ___/ ___||  _ \   _   _ _   _(_) __| |
  _|_||_| | | | \___ \___ \| |_) | | | | | | | | |/ _` |
 |_||_|_| | |_| |___) |__) |  __/  | |_| | |_| | | (_| |
  |_|_|_|  \___/|____/____/|_|      \__,_|\__,_|_|\__,_|

  OSSP uuid - Universally Unique Identifier

  OVERVIEW

  A UUID consists of 128 bits (16-octets) which are split into 6
  octet-bounded unsigned integer fields ("time_low", "time_mid",
  "time_hi_and_version", "clk_seq_hi_res", "clk_seq_low" and "node") and
  where two fields are multiplexed with a fixed size 4-bit "version" and
  a variable sized 2-3 bit "variant" field.

  The UUID octets are counted from left to right 15 to 0 and the bits
  in each octet are counted from left to right 7 to 0 (most significant
  bit first, least significant bit last). The unsigned integer fields
  formed out of multiple octets are stored in "network byte order" (most
  significant octet first, least significant octet last). A UUID is
  stored and transmitted from left to right, i.e., in "network byte
  order" with the most significant octet first and the least significant
  octet last.

  Illustration 1:
  (single octet array, less compact, more annotations)


  Bits:                                                   [4]           [2-3]
  Field:                                                version        variant
        MSO                                           -->|  |<--      -->| |<--                                                        LSO
           \                                             |  |            | |                                                          /
  Octet:    15      14      13      12      11      10   |  |9       8   | | 7       6       5       4       3       2       1       0
         +------++------++------++------++------++------++------++------++------++------++------++------++------++------++------++------+
  UUID:  |      ||      ||      ||      ||      ||      |####   ||      |##:    ||      ||      ||      ||      ||      ||      ||      |
         +------++------++------++------++------++------++------++------++------++------++------++------++------++------++------++------+
  Bit:   76543210765432107654321076543210765432107654321076543210765432107654321076543210765432107654321076543210765432107654321076543210
        /|                              ||              ||              ||      ||      ||                                              |\
     MSB |                              ||              ||              ||      ||      ||                                              | LSB
         |<---------------------------->||<------------>||<------------>||<---->||<---->||<-------------------------------------------->|
                                                           time_hi        clk_seq clk_seq
  Field:           time_low                  time_mid      _and_version   _hi_res _low                         node
  Bits:              [32]                      [16]           [16]        [5-6]     [8]                        [48]


  Illustration 2:
  (two octet arrays, more compact, less annotations)

                                                        [4]
                                                      version
                                                    -->|  |<--
                                                       |  |
                                                       |  |  [16]
                   [32]                      [16]      |  |time_hi
                 time_low                  time_mid    | _and_version
       |<---------------------------->||<------------>||<------------>|
       |    MSO                       ||              ||  |           |
       |   /                          ||              ||  |           |
       |  15      14      13      12  ||  11      10  ||  |9       8  |
       7654321076543210765432107654321076543210765432107654321076543210
      /+------++------++------++------++------++------++------++------+~
   MSB |      ||      ||      ||      ||      ||      |####   ||      |  ...
       +------++------++------++------++------++------++------++------+~
      ~+------++------++------++------++------++------++------++------+
  ...  ##:    ||      ||      ||      ||      ||      ||      ||      | LSB
      ~+------++------++------++------++------++------++------++------+/
       7654321076543210765432107654321076543210765432107654321076543210
       | | 7  ||   6  ||   5       4       3       2       1       0  |
       | |    ||      ||                                          /   |
       | |    ||      ||                                        LSO   |
       |<---->||<---->||<-------------------------------------------->|
       |clk_seq clk_seq                      node
       |_hi_res _low                         [48]
       |[5-6]    [8]
       | |
    -->| |<--
     variant
      [2-3]