--------------------------------------------------------------------- -- ##### # # ##### -- # # #### # # ###### # # ###### # # # # -- # # # # # # ## ## # # # # -- ##### # ###### ##### # ## # ##### ##### ####### ##### -- # # # # # # # # # # # -- # # # # # # # # # # # # # -- ##### #### # # ###### # # ###### # # ####### --------------------------------------------------------------------- with System; with System.Storage_Pools; with Ada.Unchecked_Conversion; -- TODO: delete these after debugging with ada.text_io; with ada.wide_text_io; with ada.integer_text_io; with ada.long_integer_text_io; --with system.address_image; -- TODO: delete above after debugging package H2.Scheme is -- An object pointer takes up as many bytes as a system word. Object_Pointer_Bits: constant := System.Word_Size; Object_Pointer_Bytes: constant := Object_Pointer_Bits / System.Storage_Unit; -- I use the lower 2 bits to indicate the type of an object pointer. -- A real object pointer is typically allocated on a word boundary. -- As a result, the lower 2 bits should always be 0. Using this -- property, I keep some other values at the lower 2 bits to indicate -- some other direct values like an integer or a character. Object_Pointer_Type_Bits: constant := 2; type Object_Pointer_Type is mod 2 ** Object_Pointer_Type_Bits; Object_Pointer_Type_Pointer: constant Object_Pointer_Type := 2#00#; Object_Pointer_Type_Integer: constant Object_Pointer_Type := 2#01#; Object_Pointer_Type_Character: constant Object_Pointer_Type := 2#10#; Object_Pointer_Type_Byte: constant Object_Pointer_Type := 2#11#; Object_Pointer_Type_Mask: constant Object_Pointer_Type := 2#11#; type Object_Record; type Object_Pointer is access all Object_Record; for Object_Pointer'Size use Object_Pointer_Bits; -- Object_Word is a numeric type as large as Object_Poinetr; type Object_Word is mod 2 ** Object_Pointer_Bits; for Object_Word'Size use Object_Pointer_Bits; -- Object_Signed_Word is the signed version of Object_Word. -- Note Object_Word is a modular type while this is a signed range. type Object_Signed_Word is range -(2 ** (Object_Pointer_Bits - 1)) .. +(2 ** (Object_Pointer_Bits - 1)) - 1; for Object_Signed_Word'Size use Object_Pointer_Bits; -- The actual number of bits for an integer the number of bits excluding -- the pointer type bits. Object_Integer_Bits: constant := Object_Pointer_Bits - Object_Pointer_Type_Bits; -- Object_Integer represents the range of SmallInteger. -- It defines an integer that can be held in the upper Object_Integer_Bits -- bits. Conversion functions betwen Object_Integer and Object_Pointer -- use the highest 1 bit to represent the sign after shifting. So, the -- range is shrunk further by 1 bit, resulting in -2 in the foluma below. -- ----------------------------------------------------------------------- -- type Object_Integer is range -(2 ** (Object_Integer_Bits - 2)) .. -- +(2 ** (Object_Integer_Bits - 2)) - 1; -- ----------------------------------------------------------------------- -- If i don't include -(2 ** (Object_Integer_Bits - 1)) into the range, -- it can be extended to a larger range. That's because the excluded number -- conflicts with the highest sign bit during the conversion process. -- ----------------------------------------------------------------------- type Object_Integer is range -(2 ** (Object_Integer_Bits - 1)) + 1 .. +(2 ** (Object_Integer_Bits - 1)) - 1; -- ----------------------------------------------------------------------- -- What is a better choice? TODO: decide what to use -- ----------------------------------------------------------------------- -- Let Object_Integer take up as large a space as Object_Pointer -- despite the actual range of Object_Integer. for Object_Integer'Size use Object_Pointer_Bits; -- The Object_Size type defines the size of object payload. -- It is the number of payload items for each object kind. --type Object_Size is new Object_Word range 0 .. (2 ** (System.Word_Size - 1)) - 1; --type Object_Size is new Object_Word range 0 .. 1000; -- TODO: remove this line and uncommect the live above type Object_Size is new Object_Word; for Object_Size'Size use Object_Pointer_Bits; -- for GC type Object_Byte is mod 2 ** System.Storage_Unit; for Object_Byte'Size use System.Storage_Unit; --subtype Object_Character is Standard.Wide_Character; --subtype Object_String is Standard.Wide_String; --package Text_IO renames Ada.Wide_Text_IO; subtype Object_Character is Standard.Character; subtype Object_String is Standard.String; package Text_IO renames Ada.Text_IO; type Object_Byte_Array is array (Object_Size range <>) of Object_Byte; type Object_Character_Array is array (Object_Size range <>) of Object_Character; type Object_Pointer_Array is array (Object_Size range <>) of Object_Pointer; type Object_Word_Array is array (Object_Size range <>) of Object_Word; type Object_Kind is ( Moved_Object, -- internal use only Pointer_Object, Character_Object, Byte_Object, Word_Object ); for Object_Kind use ( Moved_Object => 0, Pointer_Object => 1, Character_Object => 2, Byte_Object => 3, Word_Object => 4 ); -- ----------------------------------------------------------------------- -- Object_Record contains the Flags field that can be used -- freely for management purpose. The Object_Flags type -- represents the value that can be stored in this field. type Object_Flags is mod 2 ** 4; Syntax_Object: constant Object_Flags := Object_Flags'(2#0001#); type Syntax_Code is mod 2 ** 4; AND_SYNTAX: constant Syntax_Code := Syntax_Code'(0); BEGIN_SYNTAX: constant Syntax_Code := Syntax_Code'(0); CASE_SYNTAX: constant Syntax_Code := Syntax_Code'(0); COND_SYNTAX: constant Syntax_Code := Syntax_Code'(0); DEFINE_SYNTAX: constant Syntax_Code := Syntax_Code'(0); IF_SYNTAX: constant Syntax_Code := Syntax_Code'(0); LAMBDA_SYNTAX: constant Syntax_Code := Syntax_Code'(0); LET_SYNTAX: constant Syntax_Code := Syntax_Code'(0); LETAST_SYNTAX: constant Syntax_Code := Syntax_Code'(0); LETREC_SYNTAX: constant Syntax_Code := Syntax_Code'(0); OR_SYNTAX: constant Syntax_Code := Syntax_Code'(0); QUOTE_SYNTAX: constant Syntax_Code := Syntax_Code'(0); SET_SYNTAX: constant Syntax_Code := Syntax_Code'(0); type Object_Tag is ( Unknown_Object, Cons_Object, String_Object, Symbol_Object, Number_Object, Array_Object, Table_Object, Lambda_Object, Continuation_Object, Frame_Object ); type Object_Record (Kind: Object_Kind; Size: Object_Size) is record Flags: Object_Flags := 0; Scode: Syntax_Code := 0; Tag: Object_Tag := Unknown_Object; -- Object payload: -- I assume that the smallest payload is able to hold an -- object pointer by specifying the alignement attribute -- to Object_Pointer_Bytes. this implementation will break -- severely if this assumption is not correct. case Kind is when Moved_Object => New_Pointer: Object_Pointer := null; when Pointer_Object => Pointer_Slot: Object_Pointer_Array (1 .. Size) := (others => null); when Character_Object => Character_Slot: Object_Character_Array (0 .. Size) := (others => Object_Character'First); when Byte_Object => Byte_Slot: Object_Byte_Array (1 .. Size) := (others => 0); when Word_Object => Word_Slot: Object_Word_Array (1 .. Size) := (others => 0); end case; end record; for Object_Record use record Kind at 0 range 0 .. 3; -- 4 bits (0 .. 15) Flags at 0 range 4 .. 7; -- 4 bits Scode at 0 range 8 .. 11; -- 4 bits (0 .. 15) Tag at 0 range 12 .. 15; -- 4 bits (0 .. 15) -- there are still some space unused in the first word. What can i do? end record; for Object_Record'Alignment use Object_Pointer_Bytes; -- the following 3 size types are defined for limiting the object size range. subtype Empty_Object_Record is Object_Record (Byte_Object, 0); -- the number of bytes in an object header. this is fixed in size Object_Header_Bytes: constant Object_Size := Empty_Object_Record'Max_Size_In_Storage_Elements; -- the largest number of bytes that an object can hold after the header Object_Payload_Max_Bytes: constant Object_Size := Object_Size'Last - Object_Header_Bytes; -- the following types are defined to set the byte range of the object data. -- the upper bound is set to the maximum that don't cause overflow in calcuating the size in bits. -- the compiler doesn't seem to be able to return 'Size or 'Max_Size_In_Storage_Elements properly -- when the number of bits calculated overflows. subtype Byte_Object_Size is Object_Size range Object_Size'First .. (Object_Payload_Max_Bytes / (Object_Byte'Max_Size_In_Storage_Elements * System.Storage_Unit)); subtype Character_Object_Size is Object_Size range Object_Size'First .. (Object_Payload_Max_Bytes / (Object_Character'Max_Size_In_Storage_Elements * System.Storage_Unit)); subtype Pointer_Object_Size is Object_Size range Object_Size'First .. (Object_Payload_Max_Bytes / (Object_Pointer'Max_Size_In_Storage_Elements * System.Storage_Unit)); subtype Word_Object_Size is Object_Size range Object_Size'First .. (Object_Payload_Max_Bytes / (Object_Word'Max_Size_In_Storage_Elements * System.Storage_Unit)); -- ----------------------------------------------------------------------------- -- Various pointer classification and conversion procedures -- ----------------------------------------------------------------------------- function Is_Pointer (Pointer: in Object_Pointer) return Standard.Boolean; function Is_Special_Pointer (Pointer: in Object_Pointer) return Standard.Boolean; function Is_Normal_Pointer (Pointer: in Object_Pointer) return Standard.Boolean; function Is_Integer (Pointer: in Object_Pointer) return Standard.Boolean; function Is_Character (Pointer: in Object_Pointer) return Standard.Boolean; function Is_Byte (Pointer: in Object_Pointer) return Standard.Boolean; function Integer_To_Pointer (Int: in Object_Integer) return Object_Pointer; function Character_To_Pointer (Char: in Object_Character) return Object_Pointer; function Byte_To_Pointer (Byte: in Object_Byte) return Object_Pointer; function Pointer_To_Integer (Pointer: in Object_Pointer) return Object_Integer; function Pointer_To_Character (Pointer: in Object_Pointer) return Object_Character; function Pointer_To_Byte (Pointer: in Object_Pointer) return Object_Byte; pragma Inline (Is_Special_Pointer); pragma Inline (Is_Pointer); pragma Inline (Is_Integer); pragma Inline (Is_Character); pragma Inline (Integer_To_Pointer); pragma Inline (Character_To_Pointer); pragma Inline (Byte_To_Pointer); pragma Inline (Pointer_To_Integer); pragma Inline (Pointer_To_Character); pragma Inline (Pointer_To_Byte); -- ----------------------------------------------------------------------------- -- While I could define Memory_Element and Memory_Size to be -- the subtype of Object_Byte and Object_Size each, they are not -- logically the same thing. -- subtype Storage_Element is Object_Byte; -- subtype Storage_Count is Object_Size; type Memory_Element is mod 2 ** System.Storage_Unit; type Memory_Size is range 0 .. (2 ** (System.Word_Size - 1)) - 1; type Interpreter_Record is limited private; type Trait_Mask is mod 2 ** System.Word_Size; No_Garbage_Collection: constant Trait_Mask := 2 ** 0; type Option_Kind is (Trait_Option); type Option_Record (Kind: Option_Kind) is record case Kind is when Trait_Option => Trait_Bits: Trait_Mask := 0; end case; end record; -- ----------------------------------------------------------------------------- -- The nil/true/false object are represented by special pointer values. -- The special values are defined under the assumption that actual objects -- are never allocated on one of these addresses. Addresses of 0, 4, 8 are -- very low, making the assumption pretty safe. Nil_Word: constant Object_Word := 2#0000#; -- 0 --Nil_Pointer: constant Object_Pointer; --for Nil_Pointer'Address use Nil_Word'Address; --pragma Import (Ada, Nil_Pointer); True_Word: constant Object_Word := 2#0100#; -- 4 --True_Pointer: constant Object_Pointer; --for True_Pointer'Address use True_Word'Address; --pragma Import (Ada, True_Pointer); False_Word: constant Object_Word := 2#1000#; -- 8 --False_Pointer: constant Object_Pointer; --for False_Pointer'Address use False_Word'Address; --pragma Import (Ada, False_Pointer); function Object_Word_To_Pointer is new Ada.Unchecked_Conversion (Object_Word, Object_Pointer); function Object_Pointer_To_Word is new Ada.Unchecked_Conversion (Object_Pointer, Object_Word); Nil_Pointer: constant Object_Pointer := Object_Word_To_Pointer (Nil_Word); True_Pointer: constant Object_Pointer := Object_Word_To_Pointer (True_Word); False_Pointer: constant Object_Pointer := Object_Word_To_Pointer (False_Word); -- ----------------------------------------------------------------------------- procedure Open (Interp: in out Interpreter_Record; Initial_Heap_Size:in Memory_Size; Storage_Pool: in Storage_Pool_Pointer := null); procedure Close (Interp: in out Interpreter_Record); procedure Evaluate (Interp: in out Interpreter_Record); procedure Set_Option (Interp: in out Interpreter_Record; Option: in Option_Record); procedure Get_Option (Interp: in out Interpreter_Record; Option: in out Option_Record); -- ----------------------------------------------------------------------------- private type Heap_Array is array (Memory_Size range <>) of aliased Memory_Element; type Heap_Record (Size: Memory_Size) is record Space: Heap_Array (1 .. Size) := (others => 0); Bound: Memory_Size := 0; end record; for Heap_Record'Alignment use Object_Pointer_Bytes; type Heap_Pointer is access all Heap_Record; type Heap_Number is mod 2 ** 1; type Heap_Pointer_Array is Array (Heap_Number'First .. Heap_Number'Last) of Heap_Pointer; type Register_Record is limited record Code: Object_Pointer := Nil_Pointer; Envir: Object_Pointer := Nil_Pointer; Args: Object_Pointer := Nil_Pointer; Next: Object_Pointer := Nil_Pointer; end record; type Interpreter_Record is limited record Storage_Pool: Storage_Pool_Pointer := null; Trait: Option_Record (Trait_Option); Heap: Heap_Pointer_Array := (others => null); Current_Heap: Heap_Number := Heap_Number'First; Root_Table: Object_Pointer := Nil_Pointer; Symbol_Table: Object_Pointer := Nil_Pointer; Environment: Object_Pointer := Nil_Pointer; Stack: Object_Pointer := Nil_Pointer; R: Register_Record; end record; end H2.Scheme;