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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.
This commit is contained in:
Joseph Myers 2015-01-12 22:34:58 +00:00
parent ca677d3c3c
commit 34e93d6c76
4 changed files with 35 additions and 3 deletions
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10
ChangeLog
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@ -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>

2
NEWS
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@ -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

22
math/libm-test.inc
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@ -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),

4
sysdeps/ieee754/ldbl-96/s_scalblnl.c
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@ -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))