Re: [ANN] Lua 5.3.0 (work2) now available
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- Subject: Re: [ANN] Lua 5.3.0 (work2) now available
- From: Coda Highland <chighland@...>
- Date: 2014年3月25日 13:28:26 -0700
On Tue, Mar 25, 2014 at 12:29 PM, Roberto Ierusalimschy
<roberto@inf.puc-rio.br> wrote:
> Correcting some details: I guess "the former requires a single extra
> operation" only applies for constant offsets, or am I missing something?
> (For an unknown offset, I could not find a way to synthesize a logical
> shift with less than three extra operations.) But, for constant
> offsets, an integer division synthesizes an arithmetic shift with no
> extra operation.
>
> I still would like to hear about the usefulness of both shifts.
>
> -- Roberto
>
I was referring to constant offsets, yes.
Now, for me, when I'm doing operations where I'm doing a shift-right
and not already masking anyway, I DO use the >> operator
arithmetically. I tend to employ it as an integer exponentiation
operator -- x << k is the same as x * (2^k), and x >> k is the same as
floor(x / (2^k)), without the cost of actually performing an
exponentiation.
When I actually NEED a logical shift, I'm ALREADY masking, so the
underlying implementation tends to be irrelevant.
/s/ Adam