Re: Question to datatype.sgml

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