[This message was posted by Daniel Martin of DMartin <[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/bfd9f918 - PLEASE DO NOT REPLY BY MAIL.]
Hi Shashank, that's very helpful, thanks! Daniel > Hello Daniel, > > pmap will not have a fixed length of 1 or 2 bytes, it's length depends > on the number of fields in message that needs pmap bit to be present. We > need to determine from stop bit everytime. > > You can refer 1.1 spec doc: Section 10.5 Presence Map: "A presence map > is represented as a stop bit encoded entity. Logically a presence map > has an infinite suffix of zeroes. This makes it possible to truncate a > presence map that ends in a sequence where the bits are all zero. The > length of the remaining part must be a multiple of seven." > > Suppose, in one message, total 7 fields need pmap, then pmap length will > be one byte (1 stop bit and 7 pmap bit). e.g. 10011011 If in second > message, 10 fields need pmap, then pmap length will be 2 bytes. e.g. > 00011011 10010000 Now in third message, 21 fields need pmap, and last 7 > fields are having pmap bit as 0 (from encoder side), then PMAP in wire > will be 01100111 10011011. For last 7 fields, pmap bit will be taken > implicitly as 0 in decoder side. > > Regards Shashank > > > I'm trying to implement a FAST decoder for CME. I'm wondering if the > > pmap always has a fixed length of 1 or 2 byte or ｄｏ Ｉ need to > > determine from stop bit everytime？ thx! [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.
