[This message was posted by Jacob Northey of The LaSalle Technology Group <[EMAIL PROTECTED]> to the "FAST Protocol" discussion forum at http://fixprotocol.org/discuss/46. You can reply to it on-line at http://fixprotocol.org/discuss/read/d7bfaf2c - PLEASE DO NOT REPLY BY MAIL.]
1. Treating the map as a standalone operator keeps the FAST specification simple. 2. The only operators that it would make sense to combine map with would be the delta or tail operators. 3. Uses single presence map bit > sorry, I was a bit too quick posting ... > > why shouldn't map combine with other operators? > > /Rolf > > > using the pbit to distinguish between definition and reference has the > > following effects: > > > > 1. multiple pmap bits must be used to apply other operators > > 2. one pbit is used for each occurrence of a map field > > 3. the wire representation of definitions will be one byte shorter > > > > More than one pbit may be used by decimal fields. > > > > The effect of 2 and 3 is that the one byte in 3 gets amortized over 8 > > reference occurrences of the field. Less than 8 references per > > definitions results in pmap being more compact, more than 8 references > > means leading zero byte results in definition being more compact. > > > > (Nullability can be expressed for the by using a nullable > > representation for the first byte of both reference and definition) > > > > /Rolf > > > >> My vote is for the following implementation > >> > >> 1. Map should not be able to combine with other operators > >> 2. The presence bit should indicate reference or definition > >> 3. Nullable fields should be encoded as a 0 presence bit and a zero > >> reference > >> > >> Example: > >> > >> 4. Defining a new value: > >> > >> PBIT: 1 ENCODING: 0x81 0x49 0x42 0xCD > >> > >> Store the value "IBM" into cache index 1. Set field value to "IBM" > >> > >> 5. Referencing a value: > >> > >> PBIT: 0 ENCODING: 0x81 > >> > >> Set field value to cached value "IBM" > >> > >> 6. Sending a null value: > >> > >> PBIT: 0 ENCODING: 0x80 > >> > >> Set field value to null [You can unsubscribe from this discussion group by sending a message to mailto:[EMAIL PROTECTED] --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Financial Information eXchange" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/FIX-Protocol?hl=en -~----------~----~----~----~------~----~------~--~---
