Re: printf and long double

[Bogdan Cristea <cristeab@xxxxxxxxx>]

On Monday 04 October 2010 14:54:46 you wrote:
> I wish I could get 24 decimal digits precision with the current long 
> double (80-bit). I can't get more than 15 digits even in a simple division.
> I think that the extended-precision can't give more than 19 decimal 
> digits of precision (log(10,2^64)=19.2). The quadruple precision can 
> give at most 34 decimal digits (log(10,2^113)=34).
> 
> Please consider the example below:
> --------------------------------------------------
> long double a = 1.0L/7.0L;
> printf("%Lf\n",a);
> --------------------------------------------------
> 
> Can't get more than 15 digits precision....-:(
> Is this a compiler problem or libc's problem? In x86_64 machines the 
> long double values supposed to give at least 106-bit precision even when 
> implemented in software. Is gcc compliant with the quadruple notation?

Have you tried to specify manually the number of digits after the decimal 
point ?

	long double a = 1.0L/7.0L;
	printf("%'.100Lf\n",a);

On a 64 bits machine the output is:

0.1428571428571428571409210675491330277964152628555893898010253906250000000000000000000000000000000000

regards
Bogdan
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