Thread: Question to datatype.sgml
Hi,
Can you please someone elaborate what's the meaning of "even" in
datatype.sgml?
<para>
By default, floating point values are output in text form in their
shortest precise decimal representation; the decimal value produced is
closer to the true stored binary value than to any other value
representable in the same binary precision. (However, the output value is
currently never <emphasis>exactly</emphasis> midway between two
representable values, in order to avoid a widespread bug where input
routines do not properly respect the round-to-even rule.) This value will
~~~~~~~~~~~~~~~~~~~
use at most 17 significant decimal digits for <type>float8</type>
values, and at most 9 digits for <type>float4</type> values.
</para>
I think "even" means "equality" here, not "even" of "even and odd".
Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp
On 30/12/2019 01:34, Tatsuo Ishii wrote: > Hi, > > Can you please someone elaborate what's the meaning of "even" in > datatype.sgml? > > <para> > By default, floating point values are output in text form in their > shortest precise decimal representation; the decimal value produced is > closer to the true stored binary value than to any other value > representable in the same binary precision. (However, the output value is > currently never <emphasis>exactly</emphasis> midway between two > representable values, in order to avoid a widespread bug where input > routines do not properly respect the round-to-even rule.) This value will > ~~~~~~~~~~~~~~~~~~~ > use at most 17 significant decimal digits for <type>float8</type> > values, and at most 9 digits for <type>float4</type> values. > </para> > > I think "even" means "equality" here, not "even" of "even and odd". It does actually mean "even and odd". This kind of rounding is also called "Banker's Rounding". https://en.wikipedia.org/wiki/Rounding#Round_half_to_even -- Vik Fearing
> On 30/12/2019 01:34, Tatsuo Ishii wrote: >> Hi, >> >> Can you please someone elaborate what's the meaning of "even" in >> datatype.sgml? >> >> <para> >> By default, floating point values are output in text form in their >> shortest precise decimal representation; the decimal value produced is >> closer to the true stored binary value than to any other value >> representable in the same binary precision. (However, the output value is >> currently never <emphasis>exactly</emphasis> midway between two >> representable values, in order to avoid a widespread bug where input >> routines do not properly respect the round-to-even rule.) This value will >> ~~~~~~~~~~~~~~~~~~~ >> use at most 17 significant decimal digits for <type>float8</type> >> values, and at most 9 digits for <type>float4</type> values. >> </para> >> >> I think "even" means "equality" here, not "even" of "even and odd". > > > It does actually mean "even and odd". This kind of rounding is also > called "Banker's Rounding". > > https://en.wikipedia.org/wiki/Rounding#Round_half_to_even Oh, Thanks! The link is very helpful. -- Tatsuo Ishii SRA OSS, Inc. Japan English: http://www.sraoss.co.jp/index_en.php Japanese:http://www.sraoss.co.jp
Tatsuo Ishii <ishii@sraoss.co.jp> writes: >>> Can you please someone elaborate what's the meaning of "even" in >>> datatype.sgml? >>>> representable values, in order to avoid a widespread bug where input >>>> routines do not properly respect the round-to-even rule.) This value will >> It does actually mean "even and odd". This kind of rounding is also >> called "Banker's Rounding". >> https://en.wikipedia.org/wiki/Rounding#Round_half_to_even > Oh, Thanks! The link is very helpful. I think actually the standard terminology is "round-to-nearest-even". regards, tom lane
>>> It does actually mean "even and odd". This kind of rounding is also >>> called "Banker's Rounding". >>> https://en.wikipedia.org/wiki/Rounding#Round_half_to_even > >> Oh, Thanks! The link is very helpful. > > I think actually the standard terminology is "round-to-nearest-even". Ok, I will change it to "round-to-nearest-even" if there's no objection. Best regards, -- Tatsuo Ishii SRA OSS, Inc. Japan English: http://www.sraoss.co.jp/index_en.php Japanese:http://www.sraoss.co.jp
>> I think actually the standard terminology is "round-to-nearest-even". > > Ok, I will change it to "round-to-nearest-even" if there's no objection. Done. Best regards, -- Tatsuo Ishii SRA OSS, Inc. Japan English: http://www.sraoss.co.jp/index_en.php Japanese:http://www.sraoss.co.jp