[M3devel] m3cg shift value/count types

[Jay K]

It looks like what I have (shown) is correct.The shift count is always an INTEGER.32bit targets have:

Shift(Word32, Int32);
Shift(Word64, Int32);


64bit targets have:Shift(Word32, Int64);
Shift(Word64, Int64);


I might have something wrong where I didn't show.The M3CG_Ops.i3 comment is wrong.The type of the value to shift and the count are never the same.

The only place the frontend uses this is builtinWord/Shift.mg.Everywhere else, when I looked quickly, is explicit ShiftLeft or ShiftRight.For those the count is unsigned.Oh. Those look wrong too.The front end uses an integer-based subrange for the parameter:
m3front/builtinWord/Shift.mg:PROCEDURE Initialize (r: INTEGER) =...    sub := SubrangeType.New (TInt.Zero, max, Int.T, FALSE);

So it is:

32bit targets:ShiftLeft or Right(Word32, Word32);
ShiftLeft or Right(Word64, Word32);


64bit targets:ShiftLeft or Right(Word32, Word64);
ShiftLeft or Right(Word64, Word64);


which also doesn't agree with M3CG_Ops.i3.

Possibly "Rep" should abstract out the shift count type and not just the value to shift.Perhaps it should be:
32bit and 64 bit targets:ShiftLeft or Right(Word32, Word32);
ShiftLeft or Right(Word64, Word64);

and perhaps it should be:
32bit:Shift(Word32, Int32);
Shift(Word64, Int64);


64bit:Shift(Word32, Int64);
Shift(Word64, Int64);


there are arguments for various combinations and what we have isn't crazy.It just disagrees with comments in M3CG_Ops.i3.  The shift count doesn't really need to be widened to match the value.   If this were C with its prevalent "int", shift could remain just 32 bits always. (or even 16)   But Modula-3 favors INTEGER/ptrdiff_t and widening even when 32bits is plenty.


 - Jay
From: jay.krell at cornell.edu
To: m3devel at elegosoft.com
Date: Sat, 22 Sep 2012 18:00:36 +0000
Subject: [M3devel] m3cg shift value/count types




M3CG_Ops.i3:
shift        (t: IType);  (* s1.t := Word.Shift  (s1.t, s0.t); pop *)rotate       (t: IType);  (* s1.t := Word.Rotate (s1.t, s0.t); pop *)

This doesn't seem right to me.
s0 is signed.s1 is not
I have it implemented as:
#define m3_shift_T(T) static T m3_shift_##T(T value,INTEGER shift)...
where T is UINT32 or UINT64.
"shift" can vary..I'll look at the frontend...
 - Jay 		 	   		   		 	   		  
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