[PPL-devel] Precision of doubles and stdio

[Roberto Bagnara]

Hi there,

the following little program

#include <stdio.h>

int main() {
   double d;
   scanf("%lf", &d);
   printf("%.1000g\n", d);
   return 0;
}

does this on Linux/i686

$ gcc -W -Wall in.c
$ a.out
70.9
70.900000000000005684341886080801486968994140625

and does the following under Cygwin on the same machine:

roberto at quark /tmp
$ gcc -W -Wall in.c

roberto at quark /tmp
$ ./a.exe
70.9
70.90000000000000568434188608080148696899414

Why?  Is there a way to reconcile the two behaviors?
Notice that I know about the x87 and its vaguaries:
nonetheless I wonder why such a scanf immediately
followed by a printf shows a difference between
Cygwin and Linux.
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 at cs.unipr.it