Number of significand bits in long double?

Steve Kargl sgk at troutmask.apl.washington.edu
Thu Aug 4 16:57:38 GMT 2005


On Thu, Aug 04, 2005 at 10:30:02AM -0600, Lonnie VanZandt wrote:
> On Thursday 04 August 2005 10:26 am, Steve Kargl wrote:
> > Can someone confirm or refute that the long double type
> > has 53 bits in its significand on i386?  Which header
> > file in /usr/include provides this info?
> 
> Would a reference such as 
> http://babbage.cs.qc.edu/IEEE-754/IEEE-754references.html help you?
> 

No.  I have a copy of IEEE-754, which states

     All implementations conforming to this standard shall support
     the single format.  Implementations should support the extended
     format corresponding to the widest basic format supported, and
     need not support any other extended format.

FreeBSD's float type is the single format.  FreeBSD's double type
is the double format and it also coincides with extended-single
format.  Note IEEE-754 says "Implementations should support" not
"Implementations shall support".

-- 
Steve


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