Fix lround, llround missing exceptions close to overflow threshold (bug 19088).

The dbl-64, ldbl-96 and ldbl-128 implementations of lround and llround
fail to produce "invalid" exceptions in cases where the rounded result
overflows the target type, but truncating the floating-point argument
to the next integer towards zero does not overflow it (so in
particular casts do not produce such exceptions).  (This issue cannot
arise for float, or for double with 64-bit target type, or for ldbl-96
with 64-bit target type and negative arguments, because of
insufficient precision in the floating-point type for arguments with
the relevant property to exist.)

This patch fixes these problems by inserting checks for the special
cases that can occur in each implementation, and explicitly raising
FE_INVALID (and avoiding the cast if it might raise spurious
FE_INEXACT).

Tested for x86_64, x86 and mips64.

	[BZ #19088]
	* sysdeps/ieee754/dbl-64/s_lround.c: Include <fenv.h> and
	<limits.h>.
	(__lround) [FE_INVALID]: Force FE_INVALID exception when result
	overflows but exception would not result from cast.
	* sysdeps/ieee754/dbl-64/wordsize-64/s_lround.c: Include <fenv.h>
	and <limits.h>.
	(__lround) [FE_INVALID]: Force FE_INVALID exception when result
	overflows but exception would not result from cast.
	* sysdeps/ieee754/ldbl-128/s_llroundl.c: Include <fenv.h> and
	<limits.h>.
	(__llroundl) [FE_INVALID]: Force FE_INVALID exception when result
	overflows but exception would not result from cast.
	* sysdeps/ieee754/ldbl-128/s_lroundl.c: Include <fenv.h> and
	<limits.h>.
	(__lroundl) [FE_INVALID]: Force FE_INVALID exception when result
	overflows but exception would not result from cast.
	* sysdeps/ieee754/ldbl-96/s_llroundl.c: Include <fenv.h> and
	<limits.h>.
	(__llroundl) [FE_INVALID]: Force FE_INVALID exception when result
	overflows but exception would not result from cast.
	* sysdeps/ieee754/ldbl-96/s_lroundl.c: Include <fenv.h> and
	<limits.h>.
	(__lroundl) [FE_INVALID]: Force FE_INVALID exception when result
	overflows but exception would not result from cast.
	* math/libm-test.inc (lround_test_data): Add more tests.
	(llround_test_data): Likewise.

2 files changed, 42 insertions, 4 deletions

diff --git a/sysdeps/ieee754/ldbl-96/s_llroundl.c b/sysdeps/ieee754/ldbl-96/s_llroundl.c
index 8381649269..17a3ccac08 100644
--- a/sysdeps/ieee754/ldbl-96/s_llroundl.c
+++ b/sysdeps/ieee754/ldbl-96/s_llroundl.c
@@ -17,6 +17,8 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
+#include <fenv.h>
+#include <limits.h>
 #include <math.h>
 
 #include <math_private.h>
@@ -64,7 +66,14 @@ __llroundl (long double x)
 	    ++result;
 
 	  if (j0 > 31)
-	    result = (result << (j0 - 31)) | (j >> (63 - j0));
+	    {
+	      result = (result << (j0 - 31)) | (j >> (63 - j0));
+#ifdef FE_INVALID
+	      if (sign == 1 && result == LLONG_MIN)
+		/* Rounding brought the value out of range.  */
+		feraiseexcept (FE_INVALID);
+#endif
+	    }
 	}
     }
   else
diff --git a/sysdeps/ieee754/ldbl-96/s_lroundl.c b/sysdeps/ieee754/ldbl-96/s_lroundl.c
index 7a59835783..6bfc2560c3 100644
--- a/sysdeps/ieee754/ldbl-96/s_lroundl.c
+++ b/sysdeps/ieee754/ldbl-96/s_lroundl.c
@@ -17,6 +17,8 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
+#include <fenv.h>
+#include <limits.h>
 #include <math.h>
 
 #include <math_private.h>
@@ -49,6 +51,13 @@ __lroundl (long double x)
 	    }
 
 	  result = j >> (31 - j0);
+#ifdef FE_INVALID
+	  if (sizeof (long int) == 4
+	      && sign == 1
+	      && result == LONG_MIN)
+	    /* Rounding brought the value out of range.  */
+	    feraiseexcept (FE_INVALID);
+#endif
 	}
     }
   else if (j0 < (int32_t) (8 * sizeof (long int)) - 1)
@@ -66,13 +75,33 @@ __lroundl (long double x)
 	  if (j0 == 31)
 	    result = ures;
 	  else
-	    result = (ures << (j0 - 31)) | (j >> (63 - j0));
+	    {
+	      result = (ures << (j0 - 31)) | (j >> (63 - j0));
+#ifdef FE_INVALID
+	      if (sizeof (long int) == 8
+		  && sign == 1
+		  && result == LONG_MIN)
+		/* Rounding brought the value out of range.  */
+		feraiseexcept (FE_INVALID);
+#endif
+	    }
 	}
     }
   else
     {
-      /* The number is too large.  It is left implementation defined
-	 what happens.  */
+      /* The number is too large.  Unless it rounds to LONG_MIN,
+	 FE_INVALID must be raised and the return value is
+	 unspecified.  */
+#ifdef FE_INVALID
+      if (sizeof (long int) == 4
+	  && x <= (long double) LONG_MIN - 0.5L)
+	{
+	  /* If truncation produces LONG_MIN, the cast will not raise
+	     the exception, but may raise "inexact".  */
+	  feraiseexcept (FE_INVALID);
+	  return LONG_MIN;
+	}
+#endif
       return (long int) x;
     }