-- raw types for the communication protocol
 -- these are used throughout at the lowest level of the protocol
 -- essentially they are the units of packets and of messages
 -- SMG.Comms has only 2 types of packets: RSA and Serpent
 -- a message is the decrypted content of a packet
 -- S.MG, 2018

with Interfaces; use Interfaces; -- Unsigned_n and Integer_n
with Ada.Unchecked_Conversion;

package Raw_Types is
  -- no side effects or internal state
  Pragma Pure(Raw_Types);

  -- constants from SMG.COMMS standard specification
    -- size of a serpent-encrypted packet and message, in octets
    -- note that this corresponds to 1472/16 = 92 Serpent blocks
    -- NB: lengths are the same!
  SERPENT_OCTETS : constant Positive := 1472;

    -- size of a RSA-encrypted packet and message in octets and bits
  RSA_PKT_OCTETS     : constant Positive := 1470;
  RSA_MSG_OCTETS     : constant Positive := 234;
  RSA_MSG_BITS       : constant Positive := RSA_MSG_OCTETS * 8; --1872

  -- raw, low-level types
  -- all messages and packets are simply arrays of octets at low level/raw
  type Octets is array( Natural range <> ) of Interfaces.Unsigned_8;

  -- raw representations of basic types (with fixed, well-defined sizes)
  subtype Octets_1 is Octets( 1 .. 1 );
  subtype Octets_2 is Octets( 1 .. 2 );
  subtype Octets_4 is Octets( 1 .. 4 );
  subtype Octets_8 is Octets( 1 .. 8 );

  -- RSA packets and contained raw messages
  subtype RSA_Pkt is Octets( 1 .. RSA_PKT_OCTETS );
  subtype RSA_Msg is Octets( 1 .. RSA_MSG_OCTETS );

  -- Serpent packets and contained raw messages
  -- NB: length is the same but the distinction makes the code clearer
  subtype Serpent_Pkt is Octets( 1 .. SERPENT_OCTETS );
  subtype Serpent_Msg is Octets( 1 .. SERPENT_OCTETS );

  -- blind, unchecked casts ( memcpy style )
  function Cast is new Ada.Unchecked_Conversion( Integer_8  , Octets_1 );
  function Cast is new Ada.Unchecked_Conversion( Octets_1   , Integer_8 );
  function Cast is new Ada.Unchecked_Conversion( Unsigned_8 , Octets_1 );
  function Cast is new Ada.Unchecked_Conversion( Octets_1   , Unsigned_8 );

  function Cast is new Ada.Unchecked_Conversion( Integer_16 , Octets_2 );
  function Cast is new Ada.Unchecked_Conversion( Octets_2   , Integer_16 );
  function Cast is new Ada.Unchecked_Conversion( Unsigned_16, Octets_2 );
  function Cast is new Ada.Unchecked_Conversion( Octets_2   , Unsigned_16 );

  function Cast is new Ada.Unchecked_Conversion( Integer_32 , Octets_4 );
  function Cast is new Ada.Unchecked_Conversion( Octets_4   , Integer_32 );
  function Cast is new Ada.Unchecked_Conversion( Unsigned_32, Octets_4 );
  function Cast is new Ada.Unchecked_Conversion( Octets_4   , Unsigned_32 );

  -- Gnat's Float has 32 bits but this might be different with other compilers
  function Cast is new Ada.Unchecked_Conversion( Float, Octets_4 );
  function Cast is new Ada.Unchecked_Conversion( Octets_4, Float );

  function Cast is new Ada.Unchecked_Conversion( Integer_64, Octets_8 );
  function Cast is new Ada.Unchecked_Conversion( Octets_8, Integer_64 );
  function Cast is new Ada.Unchecked_Conversion( Unsigned_64, Octets_8 );
  function Cast is new Ada.Unchecked_Conversion( Octets_8, Unsigned_64 );

end Raw_Types;