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Re: Precision of doubles and stdio
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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