long double format on I!64

[Gabriel Dos Reis]

Hi,

  I've been reviewing the fundamental data types format as
communicated to V3 sources. due to some mismatch in data, we're now
getting some information directly from the compiler.  See

      http://gcc.gnu.org/ml/gcc-patches/2002-08/msg01672.html

In the file

     libstdc++-v3/config/cpu/ia64/cpu_limits.h

I see the following 

    // While sizeof(long double) == 16, the format is the same as the x86.
    #define __glibcpp_long_double_bits 80

I don't know how exactly I should interpret that since 80 bits don't
make 16 bytes.  I guess that means some bits are ignored.  If so I need
to know exactly which ones. 

Thanks,

-- Gaby