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From: Mirco Wahab on 2 Apr 2008 10:25
sisyphus wrote:
> On Apr 2, 9:21 pm, vivekanand.n...(a)gmail.com wrote:
>> printf("%.32g\n",0.99999999976716936);
>> Perl 5.6.1 output:
>> 0.99999999976716936 --> GOOD
>> Perl 5.8.6 output:
>> 0.99999999976716925 --> ERROR
> I believe it's a bug in perl 5.8 (which has been carried through to
> perl 5.10):
> C:\_32\pscrpt>perl -e "printf(\"%.32g\n\",0.99999999976716936);"
> 0.99999999976716925
> C:\_32\pscrpt>perl -e "printf(\"%.32g\n\",9.9999999976716936e-1);"
> 0.99999999976716936
>
> Since 0.99999999976716936 == 9.9999999976716936e-1, I can think of no
> good reason that that those 2 one-liners should produce different
> output - and I believe the first one liner produces an incorrect
> result.
>
> I'll submit a bug report about this - unless someone can convince me
> that it's *not* a bug (or unless someone else wants to submit the
> report).

Seems to be dependend on the underlying C library
implementation. Consider the following program round.c:
----- [round.c] -----
#include "stdio.h"
int main() {
printf("0.99999999976716936\n");
printf("%.32g | %.36f\n", 0.99999999976716936, 0.99999999976716936);
printf("%.32g | %.36f (%s)\n",9.9999999976716936e-1,9.9999999976716936e-1,"sisyphus");
return 0;
}
--------------------

Results:
=========
Linux/gcc: gcc-4.3 -o round round.c ; ./round

0.99999999976716936
0.99999999976716935634613037109375 | 0.999999999767169356346130371093750000
0.99999999976716935634613037109375 | 0.999999999767169356346130371093750000 (sisyphus)

WinXP/Visual-C++ 2005 & Visual C++6.0 (same results):

0.99999999976716936
0.99999999976716936 | 0.999999999767169360000000000000000000
0.99999999976716936 | 0.999999999767169360000000000000000000 (sisyphus)


WinXP/MinGW 3.4.2

0.99999999976716936
0.99999999976716936 | 0.999999999767169360000000000000000000
0.99999999976716936 | 0.999999999767169360000000000000000000 (sisyphus)


Regards

M.

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