[This message was posted by Shashank Bhatt of Faculties India <[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/f70386fb - PLEASE DO NOT REPLY BY MAIL.]
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.
