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- Subject: Re: [ANN] Lua 5.3.0 (work2) now available
- From: William Ahern <william@...>
- Date: Tue, 25 Mar 2014 12:25:53 -0700
On Tue, Mar 25, 2014 at 01:31:06PM -0400, Ralph Hempel wrote:
> Dirk Laurie wrote:
> >2014-03-25 18:20 GMT+02:00 Paul Baker<email@example.com>:
> >>Regarding the new bitwise operators, the Reference Manual states "Both
> >>right and left shifts fill with zeros the vacant bits". Given that
> >>"Lua 5.3 has integers but not unsigned integers" , it seems strange
> >>that the>> operator is unsigned rather than signed. Is there a reason
> >>for this? Personally, I think it would be useful for Lua to support
> >>both types of right shift - perhaps using the same syntax as
> >Don't agree.
> >I can see the point of arithmetic shift in C, where it could be useful
> >when programming multiprecision arithmetic ??? but C does not have
> >it. Its inclusion in the bit32 library always felt to me like a loving
> >preservation of a quirk of some early computer (IBM 360 springs to
> I believe that the result of a shift in C must preserve the implied
> "signedness" of the value being shifted.
> For the case of signed values, a right shift will fill high order bits with
> the value of the MSB.
Right shifting a signed type with a negative value has
Left shifting a signed type with a negative value has undefined-behavior.
See N1570 (C11) 6.5.7 p4 and p5.