Here is what happens (experiments repeated with identical results
with OpenBSD 5.1 both on x86_64 and sparc64):
-bash-4.2$ cat bug.cc
#include <cmath>
#include <cstdlib>
#include <cstdio>
int main(int argc, char **argv) {
long double x = strtold(argv[1], 0);
long double y = std::floor(x);
printf("%.1000Lg\n%.1000Lg\n", x, y);
}
-bash-4.2$ g++ bug.cc
-bash-4.2$ ./a.out 13311002825915415087
13311002825915415087
13311002825915414528
-bash-4.2$
As you can see, std::floor(x) returns a wrong result.
An equivalent C program does the right thing:
-bash-4.2$ cat bug.c
#include <math.h>
#include <stdlib.h>
#include <stdio.h>
int main(int argc, char **argv) {
long double x = strtold(argv[1], 0);
long double y = floorl(x);
printf("%.1000Lg\n%.1000Lg\n", x, y);
}
-bash-4.2$ gcc bug.c -lm
-bash-4.2$ ./a.out 13311002825915415087
13311002825915415087
13311002825915415087
-bash-4.2$
But not if it is linked with -lstdc++ instead of -lm:
-bash-4.2$ gcc bug.c -lstdc++
-bash-4.2$ ./a.out 13311002825915415087
13311002825915415087
13311002825915414528
-bash-4.2$
The reason why libstdc++ on OpenBSD exports a
bogus version of floorl() probably lies with the
following piece of code:
#ifndef HAVE_FLOORL
long double
floorl(long double x)
{
return floor((double) x);
}
#endif
It would seem that, on OpenBSD, libstdc++ is compiled
with HAVE_FLOORL not defined.
--
Roberto Bagnara
BUGSENG srl
http://bugseng.com
mailto:roberto.bagn...@bugseng.com
