[Bug math/5350] New: floor() is giving incorrect results on alpha

[Bug math/5350] New: floor() is giving incorrect results on alpha

[aurelien at aurel32 dot net]

floor() is giving wrong result for some corner cases on alpha, as shown by the 
following testcase:

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

int main() {
  double x;

  printf("%s%d\n", "DBL_MANT_DIG = ", DBL_MANT_DIG);
  x = ldexp (1.0, DBL_MANT_DIG) - 1.0;
  printf("%lf %lf\n", x, floor(x));
  assert(x == floor(x));    /* does not work in alpha */
  return 0;
}

It is actually a regression introduced by the following changesets:

2007-03-14  Richard Henderson  <rth@redhat.com>

        * sysdeps/alpha/fpu/s_ceil.c: Rewrite without branches.
        * sysdeps/alpha/fpu/s_ceilf.c: Likewise.
        * sysdeps/alpha/fpu/s_floor.c: Likewise.
        * sysdeps/alpha/fpu/s_floorf.c: Likewise.
        * sysdeps/alpha/fpu/s_rint.c: Likewise.
        * sysdeps/alpha/fpu/s_rintf.c: Likewise.

This change also assumes that the internal FPU representation has the same 
precision as the IEEE one, which is not always true.

-- 
           Summary: floor() is giving incorrect results on alpha
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
        AssignedTo: aj at suse dot de
        ReportedBy: aurelien at aurel32 dot net
                CC: glibc-bugs at sources dot redhat dot com
 GCC build triplet: alphaev68-unknown-linux-gnu
  GCC host triplet: alphaev68-unknown-linux-gnu
GCC target triplet: alphaev68-unknown-linux-gnu


http://sourceware.org/bugzilla/show_bug.cgi?id=5350

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[Bug math/5350] floor() is giving incorrect results on alpha

[aurelien at aurel32 dot net]

------- Additional Comments From aurelien at aurel32 dot net  2007-11-16 22:02 -------
Created an attachment (id=2094)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=2094&action=view)
Patch to revert the code to the old version


-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=5350

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[Bug math/5350] floor() is giving incorrect results on alpha

[aj at suse dot de]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|aj at suse dot de           |rth at redhat dot com
             Status|NEW                         |ASSIGNED


http://sourceware.org/bugzilla/show_bug.cgi?id=5350

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[Bug math/5350] floor() is giving incorrect results on alpha

[rth at gcc dot gnu dot org]

------- Additional Comments From rth at gcc dot gnu dot org  2010-05-04 16:23 -------
Patch applied: 116ff9ad1801108d084fd9ff94241f26a33dff1c

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://sourceware.org/bugzilla/show_bug.cgi?id=5350

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