Precision of doubles and stdio
Roberto Bagnara
bagnara@cs.unipr.it
Sun Mar 5 13:56:00 GMT 2006
skaller wrote:
> On Sun, 2006-03-05 at 12:44 +0100, Roberto Bagnara wrote:
>> Tim Prince wrote:
>> My
>>> past reading of various relevant documents convinced me that digits
>>> beyond the 17th in formatting of doubles are not required by any
>>> standard to be consistent between implementations. They have no useful
>>> function, as 17 digits are sufficient to determine uniquely the
>>> corresponding binary value in IEEE 754 format.
>> Thank you Tim. We were unaware of this giant bug in the C standard.
>> All the best,
>
> There is no bug in the C Standard. The C standard makes it
> clear the accuracy of floating point operations is
> implementation defined ,and the implementor may even say the
> accuracy is undefined.
Which operations are you talking about? I am not talking
about floating point operations.
> This is not a bug, it is the proper thing for a language
> standard.
Call it the way you want: I call `buggy' a standard that
allows an invocation of
printf("%.37g\n", d);
to silently ignore 20 or so significant digits (and apparently
for no good reason, by the way). You can call it `bad design',
if you prefer. Or `unfortunate legacy'. You are of course
free to call it `good design' if you like it.
All the best,
Roberto
--
Prof. Roberto Bagnara
Computer Science Group
Department of Mathematics, University of Parma, Italy
http://www.cs.unipr.it/~bagnara/
mailto:bagnara@cs.unipr.it
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