pmap doubt

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1

Imported from previous forum

2

Hi,
I had a datastream for FAST, i started decoding and reached succesfully upto this point, but after this I got confused. After using other pmap bits I have left with three bits ‘110’ and this data stream ‘01 0c f5 19 39 93 00 7d f6 92 84’. And these are the fields which I have yet to decode.

− − − − − − −

When I tried, I couldn’t match all fields with pmap. I got short of one pmap bit. Also, there is one NULL in datastream, what is the significance of this.

will anyone help me out.
Thanks,
-deepak.

3

You can really never run out of bits in the pmap since the pmap is implicitly extended with an infinite number of zero bits.

If I count the bits required by the template instructions you posted, I get it to four. So you should proceed as if your pmap was 1100.

NULL means that a value is not present and is used for fields that are specified as optional (the attribute presence=“optional” in the XML syntax)

/David

Hi, I had a datastream for FAST, i started decoding and reached
succesfully upto this point, but after this I got confused. After using
other pmap bits I have left with three bits ‘110’ and this data stream
‘01 0c f5 19 39 93 00 7d f6 92 84’. And these are the fields which I
have yet to decode. -
− −
−
− − − −

When I tried, I couldn’t match all fields with pmap. I got short of one
pmap bit. Also, there is one NULL in datastream, what is the
significance of this.

will anyone help me out. Thanks, -deepak.

4

Thanks david,
you just cleared my doubt. But as you see there is no optional fields in template definition. So, in this case this NULL corresponds to which field.
Thanks once again,
-deepak

You can really never run out of bits in the pmap since the pmap is
implicitly extended with an infinite number of zero bits.

If I count the bits required by the template instructions you posted, I
get it to four. So you should proceed as if your pmap was 1100.

NULL means that a value is not present and is used for fields that
are specified as optional (the attribute presence=“optional” in the
XML syntax)

/David

Hi, I had a datastream for FAST, i started decoding and reached
succesfully upto this point, but after this I got confused. After
using other pmap bits I have left with three bits ‘110’ and this data
stream ‘01 0c f5 19 39 93 00 7d f6 92 84’. And these are the fields
which I have yet to decode. -
−
− −
−
−
−
−

When I tried, I couldn’t match all fields with pmap. I got short of
one pmap bit. Also, there is one NULL in datastream, what is the
significance of this.

will anyone help me out. Thanks, -deepak.

5

When you say NULL I guess you mean that you see the byte 0x80 in the stream. 0x80 is only interpreted as NULL when the field is nullable. It may for example be the value zero you’re seeing for an integer field that is not nullable.

/David

Thanks david, you just cleared my doubt. But as you see there is no
optional fields in template definition. So, in this case this NULL
corresponds to which field. Thanks once again, -deepak

You can really never run out of bits in the pmap since the pmap is
implicitly extended with an infinite number of zero bits.

If I count the bits required by the template instructions you posted,
I get it to four. So you should proceed as if your pmap was 1100.

NULL means that a value is not present and is used for fields that
are specified as optional (the attribute presence=“optional” in the
XML syntax)

/David

Hi, I had a datastream for FAST, i started decoding and reached
succesfully upto this point, but after this I got confused. After
using other pmap bits I have left with three bits ‘110’ and this
data stream ‘01 0c f5 19 39 93 00 7d f6 92 84’. And these are the
fields which I have yet to decode. - −
− −
−
−
−
−

When I tried, I couldn’t match all fields with pmap. I got short of
one pmap bit. Also, there is one NULL in datastream, what is the
significance of this.

will anyone help me out. Thanks, -deepak.

6

No david,
I am referring to a ‘00’ in data, when i mapped the data bytes to the fields, I got ‘00 7d f6’ for mantissa, but the doubt is the same value can have been denoted by simply ‘7d f6’. So, why is this ‘00’.

When you say NULL I guess you mean that you see the byte 0x80 in the
stream. 0x80 is only interpreted as NULL when the field is nullable. It
may for example be the value zero you’re seeing for an integer field
that is not nullable.

/David

Thanks david, you just cleared my doubt. But as you see there is no
optional fields in template definition. So, in this case this NULL
corresponds to which field. Thanks once again, -deepak

You can really never run out of bits in the pmap since the pmap is
implicitly extended with an infinite number of zero bits.

If I count the bits required by the template instructions you
posted, I get it to four. So you should proceed as if your pmap
was 1100.

NULL means that a value is not present and is used for fields that
are specified as optional (the attribute presence=“optional” in the
XML syntax)

/David

Hi, I had a datastream for FAST, i started decoding and reached
succesfully upto this point, but after this I got confused. After
using other pmap bits I have left with three bits ‘110’ and this
data stream ‘01 0c f5 19 39 93 00 7d f6 92 84’. And these are the
fields which I have yet to decode. - −
− −
−
− − −

When I tried, I couldn’t match all fields with pmap. I got short
of one pmap bit. Also, there is one NULL in datastream, what is
the significance of this.

will anyone help me out. Thanks, -deepak.

7

It’s because the mantissa is encoded as a signed integer. If you drop the leading 00 you’ll end up with a negative number (since the sign bit, the most significant bit, is then set).

/David

No david, I am referring to a ‘00’ in data, when i mapped the data bytes
to the fields, I got ‘00 7d f6’ for mantissa, but the doubt is the same
value can have been denoted by simply ‘7d f6’. So, why is this ‘00’.