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Date: Mon, 30 Dec 2019 11:07:36 +0900 (JST)
Message-Id: <20191230.110736.1393438990550013054.t-ishii@sraoss.co.jp>
To: vik.fearing@2ndquadrant.com
Cc: pgsql-docs@lists.postgresql.org
Subject: Re: Question to datatype.sgml
From: Tatsuo Ishii <ishii@sraoss.co.jp>
In-Reply-To: <79565c24-89ed-abfd-46df-4a23cde21b04@2ndquadrant.com>
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> 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 th=
eir
>>      shortest precise decimal representation; the decimal value prod=
uced is
>>      closer to the true stored binary value than to any other value
>>      representable in the same binary precision. (However, the outpu=
t 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</typ=
e>
>>      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".=A0 This kind of rounding is als=
o
> 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