Re: Unsigned 64 bit integer to numeric - Mailing list pgsql-hackers

From Dmitry Dolgov
Subject Re: Unsigned 64 bit integer to numeric
Date
Msg-id 20191204192537.nbhjnvtcz4b2brub@localhost
Whole thread Raw
In response to Re: Unsigned 64 bit integer to numeric  (Andrew Gierth <andrew@tao11.riddles.org.uk>)
List pgsql-hackers
> On Wed, Dec 04, 2019 at 11:49:20AM +0000, Andrew Gierth wrote:
>
> >>>>> "Dmitry" == Dmitry Dolgov <9erthalion6@gmail.com> writes:
>
>  Dmitry> Hi,
>
>  Dmitry> Probably a simple question, but I don't see a simple answer so
>  Dmitry> far. In one extension I want to convert uint64 into a numeric
>  Dmitry> to put it eventually into a jsonb object. As far as I see in
>  Dmitry> numeric.c there are functions only for signed int64. Is there a
>  Dmitry> way to achive this with uint64 (without duplicating significant
>  Dmitry> part of numeric implementation in the extension)?
>
> Sure. Flip the top bit; convert the value as if signed; then subtract
> -(2^63) from the result. (Easier to subtract -(2^63) than to add 2^63,
> since the former can itself be represented in a signed int64 for easy
> conversion to numeric.)

Indeed, looks like this does the trick, thank you!



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