File: TipeDesc.i3 Last Modified On Tue Jul 5 15:39:08 PDT 1994 by kalsow
INTERFACEATipeDesc ; IMPORT Target, M3;
type description is a stream of bytes. It represents a Modula-3
type. It begins with an integer equal to the number of graph nodes,
then a preorder traversal of the corresponding AST nodes. Each of the
type constructors is represented by a single byte (=ORD(Op)) and zero
or more operands.
Integer values are encoded in a variable-length byte stream. The first byte contains two flag bits: the sign bit (s=16_80) and the special bit (x=16_40). The rest of the first byte (v=16_3f) represents the values 0..16_3f. So, given a stream x0, x1, x2, ... of 0..255 values where x0 is split into the fields (s/x/v), the represented integer value is:
(x=0) value = sign(s) * v (x=1) (v=1..8) value = sign(s) * (SUM(i=1 to v) xi<<8*i) (s=0) (x=1) (v=16_3e) value = +16_7fffffff = +2^31 - 1 (s=1) (x=1) (v=16_3e) value = -16_80000000 = -2^31 (s=0) (x=1) (v=16_3f) value = +16_7fffffffffffffff = +2^63 - 1 (s=1) (x=1) (v=16_3f) value = -16_8000000000000000 = -2^63
where sign(0)=+1, sign(1)=-1.
TYPE (* This must be kept in sync with type RTTipe.m3.Op, in runtime. *)
Op = {
(* opcode -- op --- operands ------------------- *)
Address, (* 00 *)
Array, (* 01, #elements: INT, element: TYPE *)
Boolean, (* 02 *)
Cardinal, (* 03 *)
Char, (* 04 *)
Enum, (* 05, #elements: INT *)
Extended, (* 06 *)
Integer, (* 07 *)
Longcard, (* 08 *)
Longint, (* 09 *)
Longreal, (* 0a *)
Null, (* 0b *)
Object, (* 0c, #fields: INT, {fields: TYPE} *)
OpenArray, (* 0d, #dimensions: INT, element: TYPE *)
Packed, (* 0e, bit size: INT, base type: TYPE *)
Proc, (* 0f *)
Real, (* 10 *)
Record, (* 11, #fields: INT, {fields: TYPE} *)
Ref, (* 12, self id: UID *)
Refany, (* 13 *)
Set, (* 14, #elements: INT *)
Subrange, (* 15, min, max: INT *)
UntracedRef, (* 16, self id: UID *)
(* Widechar is denoted as Enum, with #elements = 2^16.
This could be fixed by a coordinated change, here, in
Enumtype.m3, and RTTipe.m3, but would invalidate
compiled code. *)
OldN, (* 17, node #: INT *)
Old0 (* 18 *)
};(* Old1, Old2, ... Old(255-ORD(Old0)) *)
PROCEDURE Start ();
begin the construction of a description
PROCEDURE Finish (a, b, c, d: TEXT := NIL): INTEGER;
finish the description, allocate global constant space for it and emit it. Returns the offset of the generated map in the global constant pool.
PROCEDURE AddO (o: Op; type: M3.Type): BOOLEAN;
add operator 'o' to the current description. If 'type' has already been seen, adds an 'Old' opcode and returns FALSE, otherwise returns TRUE.
PROCEDURE AddU (uid: INTEGER);
add the 32-bit type 'uid' to the current description.
PROCEDURE AddI (i: INTEGER);
add integer 'i' to the current description (max 32 bits!)
PROCEDURE AddX (READONLY i: Target.Int);
add a variable length target integer 'i' to the description
PROCEDURE Reset (); END TipeDesc.