We should probably make Indexable generic as well, so that
Indexable[Int64] is something that's indexable by 64-bit values,
and Indexable[Point[Int64]] is something indexable by points with
64-bit fields...
Igor
Jeff Kuehn wrote on 07/03/2008 01:05:03 AM:
> If this means the ability to define regions with Int64 values for the
> bounds as well, it
> would be a value-add.
>
> Regards,
> --Jeff
>
> Nate Nystrom wrote:
> > Hi Vivek,
> >
> >
> > On 03 Jul 2008, at 00:38, Vivek Sarkar wrote:
> >
> >> Hi, Nate,
> >>
> >> Here's a related thought. If you're adding Int8, Int16, Int32, Int64
> >> as new value classes, it would be useful to extend them to points by
> >> adding Point8, Point16, Point32, and Point64 as well.
> >
> > Agreed. Or, we could make Point generic; that is, support
> > Point[Int32], Point[Int64], etc.
> >
> > Nate
> >
> >
> >
> >
> >>
> >> Best,
> >>
> >> Vivek
> >>
> >> On Jun 19, 2008, at 11:01 AM, Nate Nystrom wrote:
> >>
> >>> Hello,
> >>>
> >>> We're starting to look at adding support for unsigned integers to
> >>> X10. The proposal is to add the following value classes:
> >>>
> >>> Int8, Int16, Int32, Int64 - signed integers of the given widths
> >>> Nat8, Nat16, Nat32, Nat64 - unsigned integers of the given widths
> >>>
> >>> More familiar names (e.g., byte, ubyte, short, ushort) will be
> >>> supported via type aliases.
> >>>
> >>> Note that Nat16 is not the same as Char, although they may have the
> >>> same representation. In particular, toString() should differ, e.g.,
> >>> "97" rather than "a".
> >>>
> >>>
> >>> So, some questions:
> >>>
> >>> 1. How should comparisons between signed and unsigned values work?
> >>>
> >>> Consider:
> >>>
> >>> u16 = Nat16.MAX; // 2^16-1 == 0xffff;
> >>> u32 = Nat32.MAX; // 2^32-1 == 0xffffffff;
> >>> i32 = -1; // -1 == 0xffffffff;
> >>>
> >>> What is i32 < u16?
> >>>
> >>> K&R C is "unsignedness preserving":
> >>>
> >>> i32 < u16 == (nat32) i32 < (nat32) u16 == 0xffffffff < 0xffffffff
> >>> == false
> >>>
> >>> ANSI C is "value preserving":
> >>>
> >>> i32 < u16 == (int32) -1 < (int32) 0xffff == -1 < 65536 == true
> >>>
> >>> Except if the operands have the same width:
> >>>
> >>> i32 < u32 == -1 < 2^32-1 == 0xffffffff < 0xffffffff == false
> >>>
> >>> I find both the K&R rule and the ANSI rule are non-intuitive in
these
> >>> corner cases. I think the last test should return true, but it
> >>> doesn't because they have the same representation.
> >>>
> >>> So, here are some of our options:
> >>>
> >>> (a) Be unsignedness preserving in the broken K&R C way.
> >>> (b) Be value preserving in the broken ANSI C way.
> >>> (c) Be value preserving correctly (i.e., i32 < u32 == true).
> >>> (d) Disallow signed vs. unsigned comparisons, forcing the programmer
> >>> to explicitly convert.
> >>> (e) Introduce different signed and unsigned operators (probably a
bad
> >>> idea)
> >>>
> >>> C#, BTW, does (c) for 32-bit values, but (d) for 64-bit values.
> >>>
> >>> Any opinions?
> >>>
> >>>
> >>> 2. What are the conversion semantics?
> >>>
> >>> Assuming 2's complement representation, we can just truncate or sign
> >>> extend to the right width and reinterpret the bits in the new type.
> >>> When converting from a signed number to a longer unsigned, do we
sign
> >>> extend before widening or after?
> >>>
> >>> i16: int16 = -1; // 0xffff
> >>> (a) (i16 to nat32) == 0x0000ffff
> >>> (b) (i16 to nat32) == 0xffffffff
> >>>
> >>> ANSI C does (b) and I don't see a good reason to be different.
> >>>
> >>>
> >>> 3. Should we get rid of >>> as redundant, since >> on an unsigned
int
> >>> would do the same thing?
> >>>
> >>>
> >>> Thanks,
> >>> Nate
> >>>
> >>>
> >>>
-------------------------------------------------------------------------
> >>> Check out the new SourceForge.net Marketplace.
> >>> It's the best place to buy or sell services for
> >>> just about anything Open Source.
> >>> http://sourceforge.net/services/buy/index.php
> >>> _______________________________________________
> >>> X10-users mailing list
> >>> [email protected]
> >>> https://lists.sourceforge.net/lists/listinfo/x10-users
> >>>
> >>
> >>
-------------------------------------------------------------------------
> >> Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW!
> >> Studies have shown that voting for your favorite open source project,
> >> along with a healthy diet, reduces your potential for chronic
lameness
> >> and boredom. Vote Now at http://www.sourceforge.net/community/cca08
> >> _______________________________________________
> >> X10-users mailing list
> >> [email protected]
> >> https://lists.sourceforge.net/lists/listinfo/x10-users
> >>
> >
> >
> >
-------------------------------------------------------------------------
> > Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW!
> > Studies have shown that voting for your favorite open source project,
> > along with a healthy diet, reduces your potential for chronic lameness
> > and boredom. Vote Now at http://www.sourceforge.net/community/cca08
> > _______________________________________________
> > X10-users mailing list
> > [email protected]
> > https://lists.sourceforge.net/lists/listinfo/x10-users
> >
>
> --
> Jeffery A. Kuehn
> Senior HPC Evaluation Researcher
> Scientific Computing Group, National Center for Computational Sciences
> Oak Ridge National Laboratory
> One Bethel Valley Road MS6173
> Oak Ridge, TN 37831
> P:865.241.6134 F:865.241.2650
>
>
-------------------------------------------------------------------------
> Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW!
> Studies have shown that voting for your favorite open source project,
> along with a healthy diet, reduces your potential for chronic lameness
> and boredom. Vote Now at http://www.sourceforge.net/community/cca08
> _______________________________________________
> X10-users mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/x10-users
--
Igor Peshansky (note the spelling change!)
IBM T.J. Watson Research Center
XJ: No More Pain for XML's Gain (http://www.research.ibm.com/xj/)
X10: Parallel Productivity and Performance (http://x10.sf.net/)
-------------------------------------------------------------------------
Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW!
Studies have shown that voting for your favorite open source project,
along with a healthy diet, reduces your potential for chronic lameness
and boredom. Vote Now at http://www.sourceforge.net/community/cca08
_______________________________________________
X10-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/x10-users
