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 d671b11533f8eb74f81ce39da2995b83a903782b..081e0b5f0f93a71ae6c152a1406af84fa6e02360 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 35d397d1516080b8ba724707597fbbfb654a7cf1..e5fb0a0c43f9a94bbda0d8509f011135fdccfc63 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 8db1dd00a321f2998ce6e8ce22d3adfa64bf48f6..34f83c64f6e5649439fe43196170a09670ec59d3 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 fca8470cdcfda4a12a96638b63539bf0ff6d2b6a..5c2f38eafd37f541c1dc34e8f2210235b3b968ce 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))