Fix ldbl-96 scalblnl for subnormal arguments (bug 17834).

The ldbl-96 implementation of scalblnl (used for x86_64 and ia64) is
incorrect for subnormal arguments (this is a separate bug from bug
17803, which is about underflowing results).  There are two problems
with the adjustments of subnormal arguments: the "two63" variable
multiplied by is actually 0x1p52L not 0x1p63L, so is insufficient to
make values normal, and then GET_LDOUBLE_EXP(es,x), used to extract
the new exponent, extracts it into a variable that isn't used, while
the value taken to by the new exponent is wrongly taken from the high
part of the mantissa before the adjustment (hx).  This patch fixes
both those problems and adds appropriate tests.

Tested for x86_64.

	[BZ #17834]
	* sysdeps/ieee754/ldbl-96/s_scalblnl.c (two63): Change value to
	0x1p63L.
	(__scalblnl): Get new exponent of adjusted subnormal value from ES
	not HX.
	* math/libm-test.inc (scalbn_test_data): Add more tests.
	(scalbln_test_data): Likewise.

diff --git a/ChangeLog b/ChangeLog
index d671b11..081e0b5 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2015-01-12  Joseph Myers  <joseph@codesourcery.com>
+
+       [BZ #17834]
+       * sysdeps/ieee754/ldbl-96/s_scalblnl.c (two63): Change value to
+       0x1p63L.
+       (__scalblnl): Get new exponent of adjusted subnormal value from ES
+       not HX.
+       * math/libm-test.inc (scalbn_test_data): Add more tests.
+       (scalbln_test_data): Likewise.
+
 2015-01-12  Adhemerval Zanella  <azanella@linux.vnet.ibm.com>
            Stefani Seibold  <stefani@seibold.net>
 

diff --git a/NEWS b/NEWS
index 35d397d..e5fb0a0 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
+  17793, 17796, 17797, 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 8db1dd0..34f83c6 100644 (file)
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -9124,6 +9124,17 @@ static const struct test_fi_f_data scalbn_test_data[] =
 
     TEST_fi_f (scalbn, 1, 0L, 1, NO_INEXACT_EXCEPTION),
 
+    TEST_fi_f (scalbn, min_value / 2, 0, min_value / 2, NO_INEXACT_EXCEPTION),
+    TEST_fi_f (scalbn, -min_value / 2, 0, -min_value / 2, NO_INEXACT_EXCEPTION),
+    TEST_fi_f (scalbn, min_value / 2, 1, min_value, NO_INEXACT_EXCEPTION),
+    TEST_fi_f (scalbn, -min_value / 2, 1, -min_value, NO_INEXACT_EXCEPTION),
+    TEST_fi_f (scalbn, min_value * 0x0.ffffp0, 0, min_value * 0x0.ffffp0, NO_INEXACT_EXCEPTION),
+    TEST_fi_f (scalbn, -min_value * 0x0.ffffp0, 0, -min_value * 0x0.ffffp0, NO_INEXACT_EXCEPTION),
+    TEST_fi_f (scalbn, min_subnorm_value, 0, min_subnorm_value, NO_INEXACT_EXCEPTION),
+    TEST_fi_f (scalbn, -min_subnorm_value, 0, -min_subnorm_value, NO_INEXACT_EXCEPTION),
+    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, 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),
@@ -9171,6 +9182,17 @@ static const struct test_fl_f_data scalbln_test_data[] =
 
     TEST_fl_f (scalbln, 1, 0L, 1, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
 
+    TEST_fl_f (scalbln, min_value / 2, 0, min_value / 2, NO_INEXACT_EXCEPTION),
+    TEST_fl_f (scalbln, -min_value / 2, 0, -min_value / 2, NO_INEXACT_EXCEPTION),
+    TEST_fl_f (scalbln, min_value / 2, 1, min_value, NO_INEXACT_EXCEPTION),
+    TEST_fl_f (scalbln, -min_value / 2, 1, -min_value, NO_INEXACT_EXCEPTION),
+    TEST_fl_f (scalbln, min_value * 0x0.ffffp0, 0, min_value * 0x0.ffffp0, NO_INEXACT_EXCEPTION),
+    TEST_fl_f (scalbln, -min_value * 0x0.ffffp0, 0, -min_value * 0x0.ffffp0, NO_INEXACT_EXCEPTION),
+    TEST_fl_f (scalbln, min_subnorm_value, 0, min_subnorm_value, NO_INEXACT_EXCEPTION),
+    TEST_fl_f (scalbln, -min_subnorm_value, 0, -min_subnorm_value, NO_INEXACT_EXCEPTION),
+    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, 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 fca8470..5c2f38e 100644 (file)
--- a/sysdeps/ieee754/ldbl-96/s_scalblnl.c
+++ b/sysdeps/ieee754/ldbl-96/s_scalblnl.c
@@ -25,7 +25,7 @@
 #include <math_private.h>
 
 static const long double
-two63   =  4.50359962737049600000e+15,
+two63   =  0x1p63L,
 twom63  =  1.08420217248550443400e-19,
 huge   = 1.0e+4900L,
 tiny   = 1.0e-4900L;
@@ -40,7 +40,7 @@ __scalblnl (long double x, long int n)
            if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
            x *= two63;
            GET_LDOUBLE_EXP(es,x);
-           k = (hx&0x7fff) - 63;
+           k = (es&0x7fff) - 63;
            }
        if (__builtin_expect(k==0x7fff, 0)) return x+x; /* NaN or Inf */
        if (__builtin_expect(n< -50000, 0))