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FAST Protocol
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FAST Extension proposal - BITGROUP
Rolf Andersson / Pantor Engineering
28 Sep 2008 3:29AM ETAll,
this is the last of four proposals announced in a previous post.
Please review and comment.
/Rolf
EXTENSION PROPOSAL - BITGROUP (packed field)
Background
There are several examples of real FAST feeds where it would
be possible to gain compaction efficiency if FAST would allow
several fields to be packed into one or more SBIT-encoded
bytes.
Introduction
A BITGROUP packs two or more fields into one SBIT-encoded
field. Each of the bit fields will:
- have a fixed size (this is a requirement)
- normally be less than 8 bits in size (not a requirement).
Example
For example, one live feed uses tags 279, 269, 461 with
limited value domains for each of the fields.
279 UpdateAction takes one of three values (requiring 2 bits)
269 EntryType takes one of two values (requiring 1 bit)
461 CFICode takes one of two values (requiring 1 bit)
As a consequence, all three field could be encoded into one
byte if several fields of one or more bits could be grouped
together.
(As a further extension bitgroups could support embedded enums
but this isn't proposed here)
Wire representation
No new representation needed.
SBIT-encoded fields will be used.
Template Syntax
FAST Extension proposal - BITGROUP
Rolf Andersson / Pantor Engineering 28 Sep 2008 3:29AM ET
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