Floating point: just 20 digits of precision

Vincent Lefevre vincent+gcc@vinc17.org
Mon Nov 29 03:54:00 GMT 2010


On 2010-11-26 16:10:39 +0100, Marc Glisse wrote:
> On Fri, 26 Nov 2010, Elias Gabriel Amaral da Silva wrote:
> 
> >Seems to yield the same precision for long double on both ia32 and
> >amd64 - that is, just 20 digits. This seems too few, looking there:
> >
> >http://en.wikipedia.org/wiki/IEEE_754-2008#Basic_formats
> >
> >Shouldn't I expect at least more than 30 digits, on amd64?
> 
> long double would be binary80.

Not even that. In binary{k}, k is required to be either 16 or a
multiple of 32. Moreover these interchange formats use the implicit
bit, which is not the case of Intel's double-extended format.

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Vincent Lefèvre <vincent@vinc17.net> - Web: <http://www.vinc17.net/>
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