4. Standard unit pecularitiesΒΆ

In Ada, the Standard package is special: is acting such as a built-in compilation unit and is the root of all other units: these are technically child units of Standard. It is the package that defines “native” declarations such as Boolean, Integer but also Character, Wide_Wide_String and the Constraint_Error exception.

Libadalang implements this package as a special analysis unit, heavily inspired from GNAT’s own implementation of this package (see GNAT’s -gnatS flag):

package Standard is

  pragma Pure (Standard);

  type Boolean is (False, True);

  type Integer is range -(2 ** 31) .. +(2 ** 31 - 1);
  subtype Natural  is Integer range 0 .. +(2 ** 31 - 1);
  subtype Positive is Integer range 1 .. +(2 ** 31 - 1);
  type Short_Short_Integer is range -(2 ** 7) .. +(2 ** 7 - 1);
  type Short_Integer       is range -(2 ** 15) .. +(2 ** 15 - 1);
  type Long_Integer        is range -(2 ** 31) .. +(2 ** 31 - 1);
  type Long_Long_Integer   is range -(2 ** 63) .. +(2 ** 63 - 1);

  type Short_Float     is digits 6
    range -16#0.FFFF_FF#E+32 .. 16#0.FFFF_FF#E+32;
  type Float           is digits 6
    range -16#0.FFFF_FF#E+32 .. 16#0.FFFF_FF#E+32;
  type Long_Float      is digits 15
    range -16#0.FFFF_FFFF_FFFF_F8#E+256 .. 16#0.FFFF_FFFF_FFFF_F8#E+256;
  type Long_Long_Float is digits 18
    range -16#0.FFFF_FFFF_FFFF_FFFF#E+4096 ..  16#0.FFFF_FFFF_FFFF_FFFF#E+4096;

  type Character is ('A');
  type Wide_Character is ('A');
  type Wide_Wide_Character is ('A');

  package ASCII is
     NUL   : constant Character := Character'Val (16#00#);
     SOH   : constant Character := Character'Val (16#01#);
     STX   : constant Character := Character'Val (16#02#);
     ETX   : constant Character := Character'Val (16#03#);
     EOT   : constant Character := Character'Val (16#04#);
     ENQ   : constant Character := Character'Val (16#05#);
     ACK   : constant Character := Character'Val (16#06#);
     BEL   : constant Character := Character'Val (16#07#);
     BS    : constant Character := Character'Val (16#08#);
     HT    : constant Character := Character'Val (16#09#);
     LF    : constant Character := Character'Val (16#0A#);
     VT    : constant Character := Character'Val (16#0B#);
     FF    : constant Character := Character'Val (16#0C#);
     CR    : constant Character := Character'Val (16#0D#);
     SO    : constant Character := Character'Val (16#0E#);
     SI    : constant Character := Character'Val (16#0F#);
     DLE   : constant Character := Character'Val (16#10#);
     DC1   : constant Character := Character'Val (16#11#);
     DC2   : constant Character := Character'Val (16#12#);
     DC3   : constant Character := Character'Val (16#13#);
     DC4   : constant Character := Character'Val (16#14#);
     NAK   : constant Character := Character'Val (16#15#);
     SYN   : constant Character := Character'Val (16#16#);
     ETB   : constant Character := Character'Val (16#17#);
     CAN   : constant Character := Character'Val (16#18#);
     EM    : constant Character := Character'Val (16#19#);
     SUB   : constant Character := Character'Val (16#1A#);
     ESC   : constant Character := Character'Val (16#1B#);
     FS    : constant Character := Character'Val (16#1C#);
     GS    : constant Character := Character'Val (16#1D#);
     RS    : constant Character := Character'Val (16#1E#);
     US    : constant Character := Character'Val (16#1F#);
     DEL   : constant Character := Character'Val (16#7F#);
     Exclam     : constant Character := '!';
     Quotation  : constant Character := '""';
     Sharp      : constant Character := '#';
     Dollar     : constant Character := '$';
     Percent    : constant Character := '%';
     Ampersand  : constant Character := '&';
     Colon      : constant Character := ':';
     Semicolon  : constant Character := ';';
     Query      : constant Character := '?';
     At_Sign    : constant Character := '@';
     L_Bracket  : constant Character := '[';
     Back_Slash : constant Character := '\';
     R_Bracket  : constant Character := ']';
     Circumflex : constant Character := '^';
     Underline  : constant Character := '_';
     Grave      : constant Character := '`';
     L_Brace    : constant Character := '{';
     Bar        : constant Character := '|';
     R_Brace    : constant Character := '}';
     Tilde      : constant Character := '~';
     LC_A : constant Character := 'a';
     LC_B : constant Character := 'b';
     LC_C : constant Character := 'c';
     LC_D : constant Character := 'd';
     LC_E : constant Character := 'e';
     LC_F : constant Character := 'f';
     LC_G : constant Character := 'g';
     LC_H : constant Character := 'h';
     LC_I : constant Character := 'i';
     LC_J : constant Character := 'j';
     LC_K : constant Character := 'k';
     LC_L : constant Character := 'l';
     LC_M : constant Character := 'm';
     LC_N : constant Character := 'n';
     LC_O : constant Character := 'o';
     LC_P : constant Character := 'p';
     LC_Q : constant Character := 'q';
     LC_R : constant Character := 'r';
     LC_S : constant Character := 's';
     LC_T : constant Character := 't';
     LC_U : constant Character := 'u';
     LC_V : constant Character := 'v';
     LC_W : constant Character := 'w';
     LC_X : constant Character := 'x';
     LC_Y : constant Character := 'y';
     LC_Z : constant Character := 'z';
  end ASCII;

  type String is array (Positive range <>) of Character;
  pragma Pack (String);

  type Wide_String is array (Positive range <>) of Wide_Character;
  pragma Pack (Wide_String);

  type Wide_Wide_String is array (Positive range <>) of Wide_Wide_Character;

  type Duration is delta 0.000000001
    range -((2 ** 63 - 1) * 0.000000001) ..
          +((2 ** 63 - 1) * 0.000000001);
  for Duration'Small use 0.000000001;

  Constraint_Error : exception;
  Program_Error    : exception;
  Storage_Error    : exception;
  Tasking_Error    : exception;

  type Universal_Int_Type_ is range -1 .. 1;
  type Universal_Real_Type_ is digits 16;
end Standard;

Warning: this is a stub, so don’t rely on the implementation using this specific source as it could change in future versions of Libadalang. Also be aware that Libadalang will use these definitions on all platforms and for all targets: do not rely on these definitions to compute memory representation of standard entities.

Note that the Character, Wide_Character and Wide_Wide_Character types are represented with partial definitions:

type Character is ('A');
type Wide_Character is ('A');
type Wide_Wide_Character is ('A');

Defining all values for each is not realistic, as for instance Wide_Wide_Character has 4 billion values: it is not reasonable to allocate memory for all of them.