GNU C Library master sources branch master updated. glibc-2.23-7-ge2310a2

[jsm28 at sourceware dot org]

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http://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=e2310a27bede834c7b63a8bd1d659c376b6388df

commit e2310a27bede834c7b63a8bd1d659c376b6388df
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Thu Feb 18 21:52:07 2016 +0000

    Fix ldbl-128ibm truncl for non-default rounding modes (bug 19593).
    
    The ldbl-128ibm implementation of truncl is only correct in
    round-to-nearest mode (in other modes, there are incorrect results and
    overflow exceptions in some cases).  It is also unnecessarily
    complicated, rounding both high and low parts to the nearest integer
    and then adjusting for the semantics of trunc, when it seems more
    natural to take the truncation of the high part (__trunc optimized
    inline versions can be used), and the floor or ceiling of the low part
    (depending on the sign of the high part) if the high part is an
    integer, as was done for floorl and ceill.  This patch makes it use
    that simpler approach.
    
    Tested for powerpc.
    
    	[BZ #19593]
    	* sysdeps/ieee754/ldbl-128ibm/s_truncl.c (__truncl): Use __trunc
    	on high part and __floor or __ceil on low part then use
    	ldbl_canonicalize_int if needed.

diff --git a/ChangeLog b/ChangeLog
index e622d9e..1f7ba5c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
 2016-02-18  Joseph Myers  <joseph@codesourcery.com>
 
+	[BZ #19593]
+	* sysdeps/ieee754/ldbl-128ibm/s_truncl.c (__truncl): Use __trunc
+	on high part and __floor or __ceil on low part then use
+	ldbl_canonicalize_int if needed.
+
 	[BZ #19592]
 	* sysdeps/ieee754/ldbl-128ibm/s_ceill.c (__ceill): Use __ceil on
 	high and low parts then use ldbl_canonicalize_int if needed.
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_truncl.c b/sysdeps/ieee754/ldbl-128ibm/s_truncl.c
index df58b64..b7d4bb5 100644
--- a/sysdeps/ieee754/ldbl-128ibm/s_truncl.c
+++ b/sysdeps/ieee754/ldbl-128ibm/s_truncl.c
@@ -35,50 +35,22 @@ __truncl (long double x)
 			&& __builtin_isless (__builtin_fabs (xh),
 					     __builtin_inf ()), 1))
     {
-      double orig_xh;
-
-      /* Long double arithmetic, including the canonicalisation below,
-	 only works in round-to-nearest mode.  */
-
-      /* Convert the high double to integer.  */
-      orig_xh = xh;
-      hi = ldbl_nearbyint (xh);
-
-      /* Subtract integral high part from the value.  */
-      xh -= hi;
-      ldbl_canonicalize (&xh, &xl);
-
-      /* Now convert the low double, adjusted for any remainder from the
-         high double.  */
-      lo = ldbl_nearbyint (xh);
-
-      /* Adjust the result when the remainder is non-zero.  nearbyint
-         rounds values to the nearest integer, and values halfway
-         between integers to the nearest even integer.  floorl must
-         round towards -Inf.  */
-      xh -= lo;
-      ldbl_canonicalize (&xh, &xl);
-
-      if (orig_xh < 0.0)
+      hi = __trunc (xh);
+      if (hi != xh)
 	{
-	  if (xh > 0.0 || (xh == 0.0 && xl > 0.0))
-	    lo += 1.0;
+	  /* The high part is not an integer; the low part does not
+	     affect the result.  */
+	  xh = hi;
+	  xl = 0;
 	}
       else
 	{
-	  if (xh < 0.0 || (xh == 0.0 && xl < 0.0))
-	    lo -= 1.0;
+	  /* The high part is a nonzero integer.  */
+	  lo = xh > 0 ? __floor (xl) : __ceil (xl);
+	  xh = hi;
+	  xl = lo;
+	  ldbl_canonicalize_int (&xh, &xl);
 	}
-
-      /* Ensure the final value is canonical.  In certain cases,
-         rounding causes hi,lo calculated so far to be non-canonical.  */
-      xh = hi;
-      xl = lo;
-      ldbl_canonicalize (&xh, &xl);
-
-      /* Ensure we return -0 rather than +0 when appropriate.  */
-      if (orig_xh < 0.0)
-	xh = -__builtin_fabs (xh);
     }
 
   return ldbl_pack (xh, xl);

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                              |    5 +++
 sysdeps/ieee754/ldbl-128ibm/s_truncl.c |   50 +++++++-------------------------
 2 files changed, 16 insertions(+), 39 deletions(-)


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