Re: On disable_cost

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От Greg Stark
Тема Re: On disable_cost
Дата
Msg-id CAM-w4HNHGuRBq_9UPvo-sFTxBVsLRQRd0GX+-rfp=Wo1GwH6jw@mail.gmail.com
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Ответ на Re: On disable_cost  (Tom Lane <tgl@sss.pgh.pa.us>)
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I think this would be ready to abstract away behind a few functions that could always be replaced by something else later...


However on further thought I really think just using a 32-bit float and 32 bits of other bitmaps or counters would be a better approach. 


On Sun., Dec. 15, 2019, 14:54 Tom Lane, <tgl@sss.pgh.pa.us> wrote:
Thomas Munro <thomas.munro@gmail.com> writes:
> On Wed, Dec 11, 2019 at 7:24 PM Laurenz Albe <laurenz.albe@cybertec.at> wrote:
>> Doesn't that rely on a specific implementation of double precision (IEEE)?
>> I thought that we don't want to limit ourselves to platforms with IEEE floats.

> Just by the way, you might want to read the second last paragraph of
> the commit message for 02ddd499.  The dream is over, we're never going
> to run on Vax.

Still, the proposed hack is doubling down on IEEE dependency in a way
that I quite dislike, in that (a) it doesn't just read float values
but generates new ones (and assumes that the hardware/libc will react in
a predictable way to them), (b) in a part of the code that has no damn
business having close dependencies on float format, and (c) for a gain
far smaller than what we got from the Ryu code.

We have had prior discussions about whether 02ddd499 justifies adding
more IEEE dependencies elsewhere.  I don't think it does.  IEEE 754
is not the last word that will ever be said on floating-point arithmetic,
any more than x86_64 is the last CPU architecture that anyone will ever
care about.  We should keep our dependencies on it well circumscribed.

                        regards, tom lane


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