[RFH] A simple way to figure out the number of bits used by a long double

[Ed Smith-Rowland]

Ed Smith-Rowland wrote:
> Paolo Carlini wrote:
>> On 02/26/2010 01:03 PM, Andreas Schwab wrote:
>>  
>>> Paolo Carlini <paolo.carlini@oracle.com> writes:
>>>    
>>>> At the moment I'm trying to cook up something fixing that count with
>>>> LDBL_MANT_DIG, but maybe there is something simpler, maybe using
>>>> preprocessor builtins?!?
>>>>           
>>> What's wrong with LDBL_MANT_DIG?
>>>       
>> Nothing Andreas, the information is all there, essentially. I was hoping
>> in something more "clever", and closer to the actual number, including
>> the exponent, etc.
>>
>> Paolo.
>>
>>   
> Huh.  I would have *sworn* that sizeof(long double) was 10 not 16 even 
> though we know it was 80 bits.
>
> How about (in the language of numeric_limits):
>
> bits = 1     //  sign bit
>      + ::digits    //  significand bits
>      + log2(1 + ::max_exponent - ::min_exponent)  //  exponent bits
>
> There are preprocessor macros for each these things IIRC if you would 
> rather use those.
>
> Another possibility: ask our Fortran brethren who support  real*4, 
> real*8, real*10, real*16, etc.
>
> Ed
>
>
Except you probably have that already.