Big value for delta operator

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Imported from previous forum

2

[ original email was from Dmitriy Ovdienko - floppy@yandex.ru ]
Dear colleagues.

Ñlarify following moment, please:

In $6.3.7.1 of the FAST spec 1.x.07 noticed - “The size of the integer required for the delta may be larger than the specified size for the field type”. But how application should calculate value for UInt64? Int128 should be used?

It is principle question and I know that we never will use such big numbers.
But as a programmer I must ask you about boundaries condition :slight_smile:

With best regards
Ovdienko Dmitriy

3

Hi Ovdienko,

this is transparent to the application, values passed to the
encoding layer and returned from the decoding layer will be
possible to represent using u{32,64}. It is the internal
as well as the wire representation that must be able to cope
with one extra bit (~twice the value range for the respective
size values). The basic wire representation of FAST allows for
this extended range. Your implementation must be handle the
extended range. One option is to use the next larger type,
(u32->u64, u64->u128) but there is (at least) one alternative
way to do it.

In summary: Your FAST codec implementation must handle the
fact that deltas may overflow the representation used in the
application type. Your app does not.

Hope this helps.

BTW, which firm / group are you associated with?

Best,
Rolf

Dear colleagues.

Ñlarify following moment, please:

In $6.3.7.1 of the FAST spec 1.x.07 noticed - “The size of the integer
required for the delta may be larger than the specified size for the
field type”. But how application should calculate value for UInt64?
Int128 should be used?

It is principle question and I know that we never will use such big
numbers. But as a programmer I must ask you about boundaries
condition :slight_smile:

With best regards Ovdienko Dmitriy

4

[ original email was from Dmitriy Ovdienko - odp@btobits.com ]
Hi Rolf,

Thank you for your answer. I’ve understood you.

PS. I’m associated with B2BITS group.

Best regards,
Dmitriy

Hi Ovdienko,

this is transparent to the application, values passed to the encoding
layer and returned from the decoding layer will be possible to represent
using u{32,64}. It is the internal as well as the wire
representation that must be able to cope with one extra bit (~twice the
value range for the respective size values). The basic wire
representation of FAST allows for this extended range. Your
implementation must be handle the extended range. One option is to use
the next larger type, (u32->u64, u64->u128) but there is (at least) one
alternative way to do it.

In summary: Your FAST codec implementation must handle the fact that
deltas may overflow the representation used in the application type.
Your app does not.

Hope this helps.

BTW, which firm / group are you associated with?

Best, Rolf

Dear colleagues.

Ñlarify following moment, please:

In $6.3.7.1 of the FAST spec 1.x.07 noticed - “The size of the integer
required for the delta may be larger than the specified size for the
field type”. But how application should calculate value for UInt64?
Int128 should be used?

It is principle question and I know that we never will use such big
numbers. But as a programmer I must ask you about boundaries
condition :slight_smile:

With best regards Ovdienko Dmitriy