This section presents one possible approach to decoding CQG FAST messages to demonstrate the fundamental concepts involved in the process. This approach is provided for example purposes and is not definitive.
FAST processing decodes a FIX message by means of FAST templates provided by CQG. The FAST template contains the instructions to decode and reconstruct compressed message data into the FIX format and also supports repeating groups (sequences) that allow a single message to convey multiple instructions (i.e., book update, trade, high/low, etc. ).
A decoding sequence can follow the steps diagramed below; this document describes Transfer Decoding, Field Decoding, and Building the FIX message only.
Step 1. Transport –Client system receives encoded FAST message.
Step 2. Transfer Decoding
•Identify template
•Extract binary encoded bits
•Map bits to fields per template field
Step 3. Field Decoding – Apply operators to determine values per template field.
Step 4. Build FIX message.
Step 5. Process FIX message