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FAST Protocol
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Re: FAST Extension proposal - MAP
Rolf Andersson / Pantor Engineering
28 Sep 2008 4:52AM ETMaybe delta? Consider the following scenario.
You have 15000 ISIN-codes.
(index 1-127 => 1 byte, index 128-16383 => 2 bytes)
So, most of the time you will use 2 bytes to represent the index.
Now let's assume some locality in the index values used.
Given that two values are within -64 -- +63 apart, you would get
a one byte index delta instead of a two byte index value.
The back-side of this setup is that deltas <-8192 and >8191 will
need 3 bytes to be represented (because deltas are signed).
Anyway, we will most probably find use for the operators in the
map case as well.
/Rolf
> The template syntax should probably be the other way around:
>
>
>
> meaning that map would be used in the same way as other field operators.
>
> Other things to consider is whether the map operator should
> utilize a bit in the presence map. If it should use a bit, there
> are a number of options.
>
> Either we use the bit to indicate declaration (instead of using a
> special zero key), or we could combine the map operator with some
> other operator semantics.
>
> In the latter case, the most straightforawd choice would probably
> be to add copy semantics. However, it might be a bit contradictory
> since if copy was a good candidate for the usage pattern in the
> first place, it could turn out that adding the map functionality
> was of little value.
>
> /David
Re: FAST Extension proposal - MAP
Rolf Andersson / Pantor Engineering 28 Sep 2008 4:52AM ET
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