Fix ldbl-96 scalblnl underflowing results (bug 17803).

The ldbl-96 implementation of scalblnl (used for x86_64 and ia64) uses
a condition k <= -63 to determine when a standard underflowing result
tiny*__copysignl(tiny,x) should be returned.  However, that condition
corresponds to values with exponent -16446 or less, and in the case of
-16446, the correct result for round-to-nearest depends on whether the
value is exactly 0x1p-16446 (half the least subnormal) or more than
that.  This patch fixes the bug by changing the condition to k <= -64
and accordingly adjusting the exponent by 64 not 63 when converting to
a normal value.

Tested for x86_64.

	[BZ #17803]
	* sysdeps/ieee754/ldbl-96/s_scalblnl.c (twom63): Rename to
	twom64.  Adjust value to 0x1p-64L.
	(__scalblnl): Only return standard underflowing result for K <=
	-64 not K <= -63; adjust exponent for underflowing result by 64
	not 63.
	* math/libm-test.inc (scalbn_test_data): Add more tests.
	(scalbln_test_data): Likewise.

diff --git a/ChangeLog b/ChangeLog
index 081e0b5f0f93a71ae6c152a1406af84fa6e02360..e8ca56b40a2b2249cfa5fc698a1ea39f9a6646bc 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,14 @@
 2015-01-12  Joseph Myers  <joseph@codesourcery.com>
 
+       [BZ #17803]
+       * sysdeps/ieee754/ldbl-96/s_scalblnl.c (twom63): Rename to
+       twom64.  Adjust value to 0x1p-64L.
+       (__scalblnl): Only return standard underflowing result for K <=
+       -64 not K <= -63; adjust exponent for underflowing result by 64
+       not 63.
+       * math/libm-test.inc (scalbn_test_data): Add more tests.
+       (scalbln_test_data): Likewise.
+
        [BZ #17834]
        * sysdeps/ieee754/ldbl-96/s_scalblnl.c (two63): Change value to
        0x1p63L.

diff --git a/NEWS b/NEWS
index e5fb0a0c43f9a94bbda0d8509f011135fdccfc63..b7c32ad796d36dc63dac99ff5dcb3c5726ba2c8c 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -17,7 +17,7 @@ Version 2.21
   17633, 17634, 17635, 17647, 17653, 17657, 17658, 17664, 17665, 17668,
   17682, 17717, 17719, 17722, 17723, 17724, 17725, 17732, 17733, 17744,
   17745, 17746, 17747, 17748, 17775, 17777, 17780, 17781, 17782, 17791,
-  17793, 17796, 17797, 17806, 17834
+  17793, 17796, 17797, 17803, 17806, 17834
 
 * Added support for TSX lock elision of pthread mutexes on powerpc32, powerpc64
   and powerpc64le.  This may improve lock scaling of existing programs on

diff --git a/math/libm-test.inc b/math/libm-test.inc
index 34f83c64f6e5649439fe43196170a09670ec59d3..6d7ff12e044e63ec36e86bb53a4de7ed86dfc3f3 100644 (file)
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -9135,6 +9135,25 @@ static const struct test_fi_f_data scalbn_test_data[] =
     TEST_fi_f (scalbn, min_subnorm_value, MANT_DIG, min_value, NO_INEXACT_EXCEPTION),
     TEST_fi_f (scalbn, -min_subnorm_value, MANT_DIG, -min_value, NO_INEXACT_EXCEPTION),
 
+    TEST_fi_f (scalbn, min_value, -MANT_DIG, min_subnorm_value, NO_INEXACT_EXCEPTION),
+    TEST_fi_f (scalbn, -min_value, -MANT_DIG, -min_subnorm_value, NO_INEXACT_EXCEPTION),
+    TEST_fi_f (scalbn, min_value, -MANT_DIG-1, plus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fi_f (scalbn, -min_value, -MANT_DIG-1, minus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fi_f (scalbn, min_value, -MANT_DIG-2, plus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fi_f (scalbn, -min_value, -MANT_DIG-2, minus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fi_f (scalbn, min_value * 1.5, -MANT_DIG, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value * 2, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value * 2, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fi_f (scalbn, -min_value * 1.5, -MANT_DIG, -min_subnorm_value * 2, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, -min_subnorm_value * 2, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fi_f (scalbn, min_value * 1.5, -MANT_DIG-1, plus_zero, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, plus_zero, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fi_f (scalbn, -min_value * 1.5, -MANT_DIG-1, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, minus_zero, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, minus_zero, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fi_f (scalbn, min_value * 1.5, -MANT_DIG-2, plus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fi_f (scalbn, -min_value * 1.5, -MANT_DIG-2, minus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fi_f (scalbn, min_value * 1.25, -MANT_DIG, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value * 2, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fi_f (scalbn, -min_value * 1.25, -MANT_DIG, -min_subnorm_value * 2, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fi_f (scalbn, min_value * 1.25, -MANT_DIG-1, plus_zero, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, plus_zero, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fi_f (scalbn, -min_value * 1.25, -MANT_DIG-1, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, minus_zero, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, minus_zero, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fi_f (scalbn, min_value * 1.25, -MANT_DIG-2, plus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fi_f (scalbn, -min_value * 1.25, -MANT_DIG-2, minus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+
     TEST_fi_f (scalbn, 1, INT_MAX, plus_oflow, INEXACT_EXCEPTION|OVERFLOW_EXCEPTION),
     TEST_fi_f (scalbn, 1, INT_MIN, plus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
     TEST_fi_f (scalbn, max_value, INT_MAX, plus_oflow, INEXACT_EXCEPTION|OVERFLOW_EXCEPTION),
@@ -9193,6 +9212,25 @@ static const struct test_fl_f_data scalbln_test_data[] =
     TEST_fl_f (scalbln, min_subnorm_value, MANT_DIG, min_value, NO_INEXACT_EXCEPTION),
     TEST_fl_f (scalbln, -min_subnorm_value, MANT_DIG, -min_value, NO_INEXACT_EXCEPTION),
 
+    TEST_fl_f (scalbln, min_value, -MANT_DIG, min_subnorm_value, NO_INEXACT_EXCEPTION),
+    TEST_fl_f (scalbln, -min_value, -MANT_DIG, -min_subnorm_value, NO_INEXACT_EXCEPTION),
+    TEST_fl_f (scalbln, min_value, -MANT_DIG-1, plus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fl_f (scalbln, -min_value, -MANT_DIG-1, minus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fl_f (scalbln, min_value, -MANT_DIG-2, plus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fl_f (scalbln, -min_value, -MANT_DIG-2, minus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fl_f (scalbln, min_value * 1.5, -MANT_DIG, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value * 2, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value * 2, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fl_f (scalbln, -min_value * 1.5, -MANT_DIG, -min_subnorm_value * 2, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, -min_subnorm_value * 2, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fl_f (scalbln, min_value * 1.5, -MANT_DIG-1, plus_zero, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, plus_zero, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fl_f (scalbln, -min_value * 1.5, -MANT_DIG-1, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, minus_zero, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, minus_zero, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fl_f (scalbln, min_value * 1.5, -MANT_DIG-2, plus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fl_f (scalbln, -min_value * 1.5, -MANT_DIG-2, minus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fl_f (scalbln, min_value * 1.25, -MANT_DIG, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value * 2, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fl_f (scalbln, -min_value * 1.25, -MANT_DIG, -min_subnorm_value * 2, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fl_f (scalbln, min_value * 1.25, -MANT_DIG-1, plus_zero, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, plus_zero, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fl_f (scalbln, -min_value * 1.25, -MANT_DIG-1, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, -min_subnorm_value, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, minus_zero, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION, minus_zero, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fl_f (scalbln, min_value * 1.25, -MANT_DIG-2, plus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+    TEST_fl_f (scalbln, -min_value * 1.25, -MANT_DIG-2, minus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION),
+
     TEST_fl_f (scalbln, 1, INT_MAX, plus_oflow, INEXACT_EXCEPTION|OVERFLOW_EXCEPTION|ERRNO_PLUS_OFLOW),
     TEST_fl_f (scalbln, 1, INT_MIN, plus_uflow, INEXACT_EXCEPTION|UNDERFLOW_EXCEPTION|ERRNO_PLUS_UFLOW),
     TEST_fl_f (scalbln, max_value, INT_MAX, plus_oflow, INEXACT_EXCEPTION|OVERFLOW_EXCEPTION|ERRNO_PLUS_OFLOW),

diff --git a/sysdeps/ieee754/ldbl-96/s_scalblnl.c b/sysdeps/ieee754/ldbl-96/s_scalblnl.c
index 5c2f38eafd37f541c1dc34e8f2210235b3b968ce..457e999c6c9c36737e4159d909d2d8b003cd3c0a 100644 (file)
--- a/sysdeps/ieee754/ldbl-96/s_scalblnl.c
+++ b/sysdeps/ieee754/ldbl-96/s_scalblnl.c
@@ -26,7 +26,7 @@
 
 static const long double
 two63   =  0x1p63L,
-twom63  =  1.08420217248550443400e-19,
+twom64  =  0x1p-64L,
 huge   = 1.0e+4900L,
 tiny   = 1.0e-4900L;
 
@@ -52,9 +52,9 @@ __scalblnl (long double x, long int n)
        k = k+n;
        if (__builtin_expect(k > 0, 1))         /* normal result */
            {SET_LDOUBLE_EXP(x,(es&0x8000)|k); return x;}
-       if (k <= -63)
+       if (k <= -64)
            return tiny*__copysignl(tiny,x);    /*underflow*/
-       k += 63;                                /* subnormal result */
+       k += 64;                                /* subnormal result */
        SET_LDOUBLE_EXP(x,(es&0x8000)|k);
-       return x*twom63;
+       return x*twom64;
 }