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William Ahern wrote:
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<>:

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" [1], 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
JavaScript:>>   and>>>   ?

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
implementation-defined behavior.

Left shifting a signed type with a negative value has undefined-behavior.

See N1570 (C11) 6.5.7 p4 and p5.

William, thanks for the correction on my overly eager use of the word "must"

What I should have said (and what has been echoed in this thread) is that most of the production C compilers I have used implement arithmetic shift right for signed integers.

And left shifting a signed value will be undefined, yes.

Maybe if we get burned by assuming how things work, we can refer to them as singed integers :-)