Bug#136836: marked as done (libc6: pow(nan, 0) returns 0?)
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From: Joey Hess <joeyh@debian.org>
To: Debian Bug Tracking System <submit@bugs.debian.org>
Subject: libc6: pow(nan, 0) returns 0?
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Date: Mon, 04 Mar 2002 16:34:57 -0500
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Package: libc6
Version: 2.2.5-3
Severity: normal
Looks like pow(nan, 0) returns 0. It's supposed to return nan, or maybe 1.
#include <math.h>
#include <errno.h>
main(){
double nan = sqrt(-1.0);
printf("isnan: %i\n", isnan(nan));
printf("pow(nan, 0) = %d\n", pow(nan, (double) 0.0));
printf("pow(nan, 0) isnan: %i\n", isnan(pow(nan, (double) 0.0)));
}
The ANSI part of the LSB test suite doesn't like this.
-- System Information
Debian Release: 3.0
Architecture: i386
Kernel: Linux silk 2.4.18 #1 Tue Feb 26 00:23:37 EST 2002 i686
Locale: LANG=C, LC_CTYPE=C
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Date: Thu, 02 Jan 2003 13:33:45 +0900
Message-ID: <80y9645fx2.wl@oris.opensource.jp>
From: GOTO Masanori <gotom@debian.or.jp>
To: 136836-done@bugs.debian.org
Subject: Re: libc6: pow(nan, 0) returns 0?
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> Looks like pow(nan, 0) returns 0. It's supposed to return nan, or maybe 1.
>
> #include <math.h>
> #include <errno.h>
> main(){
> double nan = sqrt(-1.0);
> printf("isnan: %i\n", isnan(nan));
> printf("pow(nan, 0) = %d\n", pow(nan, (double) 0.0));
> printf("pow(nan, 0) isnan: %i\n", isnan(pow(nan, (double) 0.0)));
> }
>
> The ANSI part of the LSB test suite doesn't like this.
Your test program is wrong. Appropriate code is:
printf("pow(nan, 0) = %f\n", pow(nan, (double) 0.0));
~~
For every X, X^(0) is 1.0, so isnan() returns 0.
In addition, if (_LIB_VERSION == _SVID_ & _XOPEN_) is defined, isnan()
returns non 0 and pow() returns NaN. You can look this behavior on
Solaris.
I don't have IEEE754 and ANSI floating point issue, so I don't know
whether ANSI defines this behavior or not. If you have IEEE754 or any
related standards, and if such standards say pow(NaN, 0) have to
return NaN, reopen this bug. We can fix easily if an appropriate
information is supplied.
I close this bug.
Regards,
-- gotom
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