[M3devel] libm3/Swap?

[Jay K]

libm3/.../swap.m3:


FROM Word IMPORT Or, And, Not, LeftShift, RightShift, Extract;


CONST
  B0 = 16_FF;
  B1 = 16_FF00;
  B2 = 16_FF0000;
  B3 = 16_FF000000;


  (* These will all be zero on machines with BYTESIZE(INTEGER) = 32 *)
  B4 = LeftShift(B3, 8);
  B5 = LeftShift(B4, 8);
  B6 = LeftShift(B5, 8);
  B7 = LeftShift(B6, 8);

CONST SignExt32 = ARRAY [0..1] OF Word.T {0, Not(16_FFFFFFFF)};

(* Swaps the lower 4 bytes of i *)
PROCEDURE Swap4 (i: Int32): Int32 =
  BEGIN
    IF BYTESIZE(INTEGER) = 4 THEN
      RETURN Or(Or(RightShift(And(B3, i), 24), RightShift(And(B2, i), 8)),
                Or(LeftShift(And(B1, i), 8), LeftShift(And(B0, i), 24)));
    ELSIF BYTESIZE(INTEGER) = 8 THEN
      RETURN
        Or(SignExt32[Extract(i, 7, 1)],
           Or(Or(RightShift(And(B3, i), 24), RightShift(And(B2, i), 8)),
              Or(LeftShift(And(B1, i), 8), LeftShift(And(B0, i), 24))));
    ELSE
      RAISE Failure;
    END;
  END Swap4;


What is the meaning of the 7?
  In Extract(i, 7, 1)?
Presumably it should be 63??
I guess I'll write a test..


Is there a better idiom that doesn't expose  architectures to compile code for other word sizes?
Maybe fork the file and include_dir(WORD_SIZE)?
 Like is done in m3core/src/C?
 

 - Jay