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Fix ldbl-96 scalblnl underflowing results (bug 17803) [committed]
- From: Joseph Myers <joseph at codesourcery dot com>
- To: <libc-alpha at sourceware dot org>
- Date: Mon, 12 Jan 2015 23:03:01 +0000
- Subject: Fix ldbl-96 scalblnl underflowing results (bug 17803) [committed]
- Authentication-results: sourceware.org; auth=none
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. Committed.
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.
diff --git a/math/libm-test.inc b/math/libm-test.inc
index 34f83c6..6d7ff12 100644
--- 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 5c2f38e..457e999 100644
--- 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;
}
--
Joseph S. Myers
joseph@codesourcery.com