Quote from IpToCountry_v3.dat.SPECS.txt

GeoIP section

-------------



The GeoIP structure contains a series of GeoID tables with content

structured in the following way. The number of IP Blocks varies between

each table.



  Field           | Size        | Description

  --------------------------------------------

  Location ID     | STRING      | This is usually a 3-character code of

                  |             | the location. For countries this is the

                  |             | ISO ALPHA-3 Code. Doomseeker matches

                  |             | country flags to IPs basing on this code.

                  |             | Usually only the political country entities

                  |             | are present here, however an exception for

                  |             | this is a generic location somewhere in

                  |             | the European Union that is expressed as

                  |             | a 2-character STRING "EU".

                  |             |

  IP Blocks Count | ULONG       | Amount of IP Blocks for this GeoID

                  |             |

  IP Blocks       | 8 * <Count> | Pairs of IPs repeating as many times

                  |             | as specified by the "Count" field.



A singular "IP Block" structure denotes a range of IPs understood as a set

of continuous integer numbers beginning from the "Begin" IPv4 and ending

on the "End" IPv4. A GeoID can have many non-continuous IPv4 addresses

assigned to it, so while the continuous range can be expressed as a min-max

integer pair, the non-continuous ranges are expressed as separate blocks.



  Field | Size  | Description

  ----------------------------

  Begin | ULONG | First IPv4 in the block, inclusive

  End   | ULONG | Final IPv4 in the block, inclusive





In current version (3) of the database the data is not presented in any

particular order. Doomseeker's parser loads the data into hashtables

where it is eventually ordered solely by the "IP Block Begin" value

with GeoID information duplicated for each non-continuous block

belonging to the same GeoID.

Quote from IpToCountry_v3.dat.SPECS.txt

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