Re: Abbreviated keys for Numeric

On Mon, Mar 23, 2015 at 3:07 PM, Peter Geoghegan <pg@heroku.com> wrote:
> On Mon, Mar 23, 2015 at 12:04 PM, Robert Haas <robertmhaas@gmail.com> wrote:
>> In my opinion, Andrew's version is far clearer.  Peter's version is
>> full of jargon that I can't understand.  I could probably figure it
>> out with a few hours and a search engine, but that really shouldn't be
>> necessary.
>
> Really?

Since I'm not in the habit of posting things to the list that I don't
really believe, it shouldn't so often be necessary to ask me if I
really meant it.  If I posted it, and it wasn't April 1st, I meant it.

> Andrew's version doesn't even explain what excess-K is. Surely
> that's obscure jargon that requires an explanation.

Well, it's possible to infer it from what he wrote afterwards, and if
you don't, you can still pretty much understand the main thrust of
what it's doing and why. I bet that could be rewritten to avoid using
the term altogether, but even if not it's pretty clear.

I don't really want to get into a nitpicking session here, but if
you're wondering what I don't like as well about your version, it's
things like this:

+ (7 binary digits is
+ * the smallest number of digits that allows us to represent weights
+ * -44 to 83 inclusive).

This isn't a stupid comment, but it also isn't really commenting on
the right thing.  I mean, -44 to 83 is a range of 128 possible
integers, so obviously it's going to need 7 bits to represent it,
because 2^7=128.  So, whatever information this is trying to convey,
it's not quite succeeding.  It's also a forward reference, because you
haven't yet given any clue what's interesting about  why we are trying
to represent a value between -44 and 83.

A bit further down:

As
+ * with IEEE-754, we use an exponent without a sign (a 7-bit exponent
+ * without a sign).

As to the beginning of this sentence, bringing IEEE-754 into this
discussion doesn't clarify anything in my mind.  I don't think most
people reading these comments are likely to be familiar with IEEE-754,
or want to go look it up.  As to the end of the sentence, writing "an
exponent without a sign" and then describing that as "a 7-bit exponent
without a sign" is extremely redundant.  Perhaps you were trying to
say that we are similar to IEEE-754 in that we use an exponent without
a sign (whatever that means) but different in that we ours is 7-bits,
but it's not really clear.

I offer these not in the spirit of asking you to correct these
specific things but just of explaining generally the sort of thing
that causes me to prefer Andrew's version.  Hope that's helpful.

-- 
Robert Haas
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