-- Ada implementation of the Mersenne Twister Pseudo-Random number generator
 -- S.MG, 2018

with Interfaces; use Interfaces;

package MT is
  -- Interfaces.Unsigned_32 in GNAT is mod 2**32 and has bitwise shifts defined
  subtype U32 is Interfaces.Unsigned_32;

  -- period parameters
  N          : constant := 624;
  M          : constant := 397;
  MATRIX_MASK: constant U32 := 16#9908_b0df#;
  UPPER_MASK : constant U32 := 16#8000_0000#;
  LOWER_MASK : constant U32 := 16#7fff_ffff#;

  -- array type for storing the state vector of the generator
  type State_Type is Array( 0 .. N-1 ) of U32;

  -- array type for initialization by array - change key len here if needed
  KEY_LEN    : constant := 4;
  type Init_Array_Type is Array( 0 .. KEY_LEN - 1 ) of U32;

  -- exception raised by a call to generator before initializing it
  No_Init_Exception : exception;

  -- initialize the generator with a seed (number)
  procedure Init_Genrand(Seed : in U32);

  -- initialize the generator with array of 8-octets elements
  procedure Init_Genrand(Seed : in Init_Array_Type);

  -- generate the next pseudo-random 32 bits number in the sequence
  function Gen_U32 return U32;

  -- for testing
  function Get_State return State_Type;

  -- internals of the generator, NOT for direct access
private
  -- actual state of the generator
  State      : State_Type;

  -- flag for generator routine
  Mti_Flag : U32 := N + 1;  -- default value -> state(N) is not initialised

end MT;