Re: asinh() gives NaN on Linux/x86/glibc with optimization on

Re: asinh() gives NaN on Linux/x86/glibc with optimization on

[Shimpei Yamashita]

H.J. Lu <hjl@lucon.org> writes:
[me saying asinh of negative number gives wrong answer]
>
># gcc -v
>Reading specs from /usr/lib/gcc-lib/i586-pc-linux/egcs-2.91.60/specs
>gcc version egcs-2.91.60 19981201 (egcs-1.1.1 release)
># gcc -O6 x.c
># a.out
>Input argument for asinh: -100
>asinh(-100.000000)=-5.298342
># ldd a.out
>        libc.so.6 => /lib/libc.so.6 (0x40007000)
>	/lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x2aaaa000)
># ls -l /lib/libc.so.6
>lrwxrwxrwx   1 root     root           26 Dec 11 08:16 /lib/libc.so.6 ->
>glibc-2.0-981211/libc.so.6
>
>I am running glibc 2.0.7 981211.

Hmm. That's funny. That's exactly what I did and I get NaN's for
answer. I'm using the version of glibc that came with RedHat 5.2, so
maybe that's the problem. OTOH, what kind of a bug in the library
would cause different optimizations in the *calling* program to give
different results?

BTW, where do I get the new snapshots of glibc? The snapshot
repository in ftp.kernel.org doesn't seem to be updated anymore.

-- 
Shimpei Yamashita               < http://www.submm.caltech.edu/%7Eshimpei/ >

Re: asinh() gives NaN on Linux/x86/glibc with optimization on

[Jeffrey A Law]

  In message < 75ph1i$phv@gap.cco.caltech.edu >you write:
  > H.J. Lu <hjl@lucon.org> writes:
  > [me saying asinh of negative number gives wrong answer]
  > >
  > ># gcc -v
  > >Reading specs from /usr/lib/gcc-lib/i586-pc-linux/egcs-2.91.60/specs
  > >gcc version egcs-2.91.60 19981201 (egcs-1.1.1 release)
  > ># gcc -O6 x.c
  > ># a.out
  > >Input argument for asinh: -100
  > >asinh(-100.000000)=-5.298342
  > ># ldd a.out
  > >        libc.so.6 => /lib/libc.so.6 (0x40007000)
  > >	/lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x2aaaa000)
  > ># ls -l /lib/libc.so.6
  > >lrwxrwxrwx   1 root     root           26 Dec 11 08:16 /lib/libc.so.6 ->
  > >glibc-2.0-981211/libc.so.6
  > >
  > >I am running glibc 2.0.7 981211.
  > 
  > Hmm. That's funny. That's exactly what I did and I get NaN's for
  > answer. I'm using the version of glibc that came with RedHat 5.2, so
  > maybe that's the problem. OTOH, what kind of a bug in the library
  > would cause different optimizations in the *calling* program to give
  > different results?
  > 
  > BTW, where do I get the new snapshots of glibc? The snapshot
  > repository in ftp.kernel.org doesn't seem to be updated anymore.
I presume you're running glibc-2.0.7?

  Here's an analysis of an earlier problem with asinh with glibc-2.0.7:
  I think I've figured it out, but looking at the x86 assembly code
  actually wasn't that much help, since the code is correct.  The
  problem is glibc 2.0.7's inline definition of asinh() in
  /usr/include/__math.h.  This definition has a misplaced paren which
  breaks it for negative arguments.  The inline definition is not
  included when compiling under gcc 2.7.x, but is included when running
  newer versions of gcc or egcs.  Since the inline definition is only
  used when optimization is turned on, and since the actual library
  definition of asinh() in glibc is apparently correct, the bug only
  shows up when optimizing.

  Here's glibc 2.0.7's definition of asinh() from /usr/include/__math.h:

  __MATH_INLINE double asinh (double __x);
  __MATH_INLINE double
  asinh (double __x)
  {
    register double __y = fabs (__x);

    return log1p ((__y * __y / (sqrt (__y * __y + 1.0) + 1.0) + __y)
                  * __sgn1 (__x));
  }

  Here's a correct definition:

  __MATH_INLINE double asinh (double __x);
  __MATH_INLINE double
  asinh (double __x)
  {
    register double __y = fabs (__x);

    return log1p ((__y * __y / (sqrt (__y * __y + 1.0) + 1.0) + __y))
                  * __sgn1 (__x);
  }

  The __sgn1() function (which computes the sign of its argument) should
  go outside the log1p(), not inside it.  The argument of log1p() is
  supposed to be positive here.  The __sgn1() is meant to invert the
  sign of the result for negative arguments of asinh(), since asinh(-x)
  = -asinh(x).

  (Actually this correction gives an extra pair of parens around the
  argument of log1p(), which could be removed.)

Re: asinh() gives NaN on Linux/x86/glibc with optimization on

[H.J. Lu]

>   Here's glibc 2.0.7's definition of asinh() from /usr/include/__math.h:
> 
>   __MATH_INLINE double asinh (double __x);
>   __MATH_INLINE double
>   asinh (double __x)
>   {
>     register double __y = fabs (__x);
> 
>     return log1p ((__y * __y / (sqrt (__y * __y + 1.0) + 1.0) + __y)
>                   * __sgn1 (__x));
>   }
> 
>   Here's a correct definition:
> 
>   __MATH_INLINE double asinh (double __x);
>   __MATH_INLINE double
>   asinh (double __x)
>   {
>     register double __y = fabs (__x);
> 
>     return log1p ((__y * __y / (sqrt (__y * __y + 1.0) + 1.0) + __y))
>                   * __sgn1 (__x);
>   }
> 
>   The __sgn1() function (which computes the sign of its argument) should
>   go outside the log1p(), not inside it.  The argument of log1p() is
>   supposed to be positive here.  The __sgn1() is meant to invert the
>   sign of the result for negative arguments of asinh(), since asinh(-x)
>   = -asinh(x).
> 
>   (Actually this correction gives an extra pair of parens around the
>   argument of log1p(), which could be removed.)
> 

1998-10-26  Ulrich Drepper  <drepper@cygnus.com>
          
        * sysdeps/i386/fpu/__math.h (asinh): Put __sgn1 call outside log1p
        call.


-- 
H.J. Lu (hjl@gnu.org)

Re: asinh() gives NaN on Linux/x86/glibc with optimization on

[Horst von Brand]

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Shimpei Yamashita <shimpei+usenet+.mil+.gov@BOFH.submm.caltech.edu> said:
> H.J. Lu <hjl@lucon.org> writes:
> >> On RedHat Linux 5.2 (using glibc 2.0.7) for x86, asinh() returns NaN
> >> for negative arguments if optimizations are on. The error does not
> >> occur if optimizations are turned off. I'm not sure where the problem
> >> is--egcs or glibc. Using libc5 seems to solve the problem, but so does
> >> dropping back to gcc 2.7.2.

The case given works reasonably with egcs-19981213, glibc-2.0.108 with -O2
-fomit-frame-pointer and without optimization (non-inlined asinh()).
-- 
Horst von Brand                             vonbrand@sleipnir.valparaiso.cl
Casilla 9G, Viña del Mar, Chile                               +56 32 672616

Re: asinh() gives NaN on Linux/x86/glibc with optimization on

[H.J. Lu]

> 
> H.J. Lu <hjl@lucon.org> writes:
> >
> >> 
> >> On RedHat Linux 5.2 (using glibc 2.0.7) for x86, asinh() returns NaN
> >> for negative arguments if optimizations are on. The error does not
> >> occur if optimizations are turned off. I'm not sure where the problem
> >> is--egcs or glibc. Using libc5 seems to solve the problem, but so does
> >> dropping back to gcc 2.7.2.
> >
> >Do you have a testcase?
> 
> Sure.
> 
> #include <stdio.h>
> #include <math.h>
> 
> main() {
> 
>   double ha;
> 
>   printf("Input argument for asinh: ");
>   scanf("%lf", &ha);
>   printf("asinh(%f)=%f\n", ha, asinh(ha));
>   exit(0);
> }
> 
> The program works correctly for positive arguments. Negative results
> (I tried -100, -50, -10, -5) all return NaN.
> 

# gcc -v
Reading specs from /usr/lib/gcc-lib/i586-pc-linux/egcs-2.91.60/specs
gcc version egcs-2.91.60 19981201 (egcs-1.1.1 release)
# gcc -O6 x.c
# a.out
Input argument for asinh: -100
asinh(-100.000000)=-5.298342
# ldd a.out
        libc.so.6 => /lib/libc.so.6 (0x40007000)
	/lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x2aaaa000)
# ls -l /lib/libc.so.6
lrwxrwxrwx   1 root     root           26 Dec 11 08:16 /lib/libc.so.6 -> glibc-2.0-981211/libc.so.6

I am running glibc 2.0.7 981211.


-- 
H.J. Lu (hjl@gnu.org)

Re: asinh() gives NaN on Linux/x86/glibc with optimization on

[Shimpei Yamashita]

H.J. Lu <hjl@lucon.org> writes:
>
>> 
>> On RedHat Linux 5.2 (using glibc 2.0.7) for x86, asinh() returns NaN
>> for negative arguments if optimizations are on. The error does not
>> occur if optimizations are turned off. I'm not sure where the problem
>> is--egcs or glibc. Using libc5 seems to solve the problem, but so does
>> dropping back to gcc 2.7.2.
>
>Do you have a testcase?

Sure.

#include <stdio.h>
#include <math.h>

main() {

  double ha;

  printf("Input argument for asinh: ");
  scanf("%lf", &ha);
  printf("asinh(%f)=%f\n", ha, asinh(ha));
  exit(0);
}

The program works correctly for positive arguments. Negative results
(I tried -100, -50, -10, -5) all return NaN.

-- 
Shimpei Yamashita               < http://www.submm.caltech.edu/%7Eshimpei/ >

Re: asinh() gives NaN on Linux/x86/glibc with optimization on

[H.J. Lu]

> 
> On RedHat Linux 5.2 (using glibc 2.0.7) for x86, asinh() returns NaN
> for negative arguments if optimizations are on. The error does not
> occur if optimizations are turned off. I'm not sure where the problem
> is--egcs or glibc. Using libc5 seems to solve the problem, but so does
> dropping back to gcc 2.7.2.

Do you have a testcase?

-- 
H.J. Lu (hjl@gnu.org)

asinh() gives NaN on Linux/x86/glibc with optimization on

[Shimpei Yamashita]

On RedHat Linux 5.2 (using glibc 2.0.7) for x86, asinh() returns NaN
for negative arguments if optimizations are on. The error does not
occur if optimizations are turned off. I'm not sure where the problem
is--egcs or glibc. Using libc5 seems to solve the problem, but so does
dropping back to gcc 2.7.2.

-- 
Shimpei Yamashita               < http://www.submm.caltech.edu/%7Eshimpei/ >