Field Content [Empty]

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1

Imported from previous forum

2

Hi!

My interpretation of the FAST Field Encoding Specification is that a Field Content with the value [Empty] is to be transfered as a NULL value, but another interpretation is that the presence map bit is to be set to not included for the field which is empty.

Is my interpretation correct? My rationlization is that if a field is not present in the presence map then there really is no value and thus no information available, but a NULL value can signal for example the copy operator to use the value previously stored in the dictionary.

3

[ original email was from Matt Simpson - msimpson@cme.com ]
Please refer to the FAST v1.1 spec at fixprotol.org/fast. An empty string is encoded as 0x00 for a non-nullable field and 0x00 0x00 for a nullable field. See page 24 of the spec. A NULL value is represented as 0x00 for a nullable field.

Standard rules apply for pmap usage for empty strings. If an operator isn’t specified then a pmap slot is not needed. See pages 21 and 40 of the spec for more information.

Hi!

My interpretation of the FAST Field Encoding Specification is that a
Field Content with the value [Empty] is to be transfered as a NULL
value, but another interpretation is that the presence map bit is to be
set to not included for the field which is empty.

Is my interpretation correct? My rationlization is that if a field is
not present in the presence map then there really is no value and thus
no information available, but a NULL value can signal for example the
copy operator to use the value previously stored in the dictionary.

4

It’s the other way round:

missing (NULL) values → pmap=1 and value=NULL
defaulted values → pmap=0 and no value in the stream

/Rolf

Hi!

My interpretation of the FAST Field Encoding Specification is
that a Field Content with the value [Empty] is to be transfered
as a NULL value, but another interpretation is that the presence
map bit is to be set to not included for the field which is empty.

Is my interpretation correct? My rationlization is that if a field
is not present in the presence map then there really is no value
and thus no information available, but a NULL value can signal for
example the copy operator to use the value previously stored in
the dictionary.