From: Chrysostomos Nanakos <nanakos@wired-net.gr>
To: Bogdan Cristea <cristeab@gmail.com>
Cc: linux-c-programming@vger.kernel.org
Subject: Re: printf and long double
Date: Mon, 04 Oct 2010 15:12:35 +0300 [thread overview]
Message-ID: <4CA9C4B3.6040906@wired-net.gr> (raw)
In-Reply-To: <201010041503.27721.cristeab@gmail.com>
On 4/10/2010 3:03 μμ, Bogdan Cristea wrote:
> 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
Of course I did. But the result you get is the wrong one after the first
20 decimal point digits. The right result is given below with a high
precision arithmetic library or with Mathematica or Matlab. And the
three results are the same, but not the given one above which is the
same for my machine.
0.14285714285714285714285714285714285714285714285714285714285714285714\
28571428571428571428571428571429
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next prev parent reply other threads:[~2010-10-04 12:12 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-03 22:56 printf and long double Nanakos Chrysostomos
2010-10-04 0:43 ` Gedare Bloom
2010-10-04 1:44 ` Glynn Clements
2010-10-04 1:33 ` Glynn Clements
2010-10-04 11:54 ` Chrysostomos Nanakos
2010-10-04 12:03 ` Bogdan Cristea
2010-10-04 12:12 ` Chrysostomos Nanakos [this message]
2010-10-06 20:18 ` printf and long double [SOLVED] Nanakos Chrysostomos
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