Re: [ANN] Lua 5.2.0 (work1) now available

[Doug Rogers <doug.rogers@...>]

Mike Pall wrote:
> Also, considering the readability aspect, what does this do:
>   bit.bshift(x, -8)  ??
> Shift right by 8? Shift left by 8? I'm sure I'm not the only one
> who had to look it up in the manual.
> ...
>  bit.lshift(x, 8)  vs.  bit.rshift(x, 8) 
> Readibility is important. And having two functions avoids an
> unpredictable branch, too. Ditto for rotates.

I agree.

> Summary:
> - Inputs to bit operations need to be converted in a consistent and
>   platform-independent way, respecting modular arithmetic requirements.
> - Outputs of bit operations need to be signed.
> - Shift and rotate instructions need to be explicitly named.
> -*Shift counts should be masked by the bit width.
> - Arithmetic right shift is not optional.
> - Ignoring the naming conventions defined by the most popular
>   existing libraries is unwise, because it forces all users to
>   rewrite their code (FYI: BitOp inherited the names from lbitlib).

A much better rant, IMO.

I'll need to go back and read your original reasoning on (*) 'Shift
counts should be masked by the bit width', because I would think the
masking should occur only for rotates. For shifts, the return value of a
overshift should be zero (or all ones, a.k.a. -1 according to the
Summary, for a sign-extended right shift with a sign bit of one).

Doug

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