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Allow spurious underflow / inexact for ldbl-128ibm.

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A large number of the test-ldouble failures seen for ldbl-128ibm are
spurious "underflow" and "inexact" exceptions.  These arise from such
exceptions in the underlying arithmetic; unlike other spurious
exceptions from that arithmetic, they do not in general relate to
cases where the returned result is also substantially inaccurate, are
not so readily avoidable by appropriately conditional libgcc patches,
and are widespread enough to be hard to handle through individual
XFAILing of the affected tests.

Thus, this patch documents relaxed accuracy goals for libm functions
for IBM long double and makes libm-test.inc reflect these spurious
exceptions in ldbl-128ibm arithmetic and always allow them in
ldbl-128ibm testing (while still not allowing these exceptions to be
missing where required to be present).  Tested for powerpc.

	* manual/math.texi (Errors in Math Functions): Document relaxed
	accuracy goals for IBM long double.
	* math/libm-test.inc (test_exceptions): Always allow spurious
	"underflow" and "inexact" exceptions for IBM long double.
This commit is contained in:
Joseph Myers 2016-03-10 23:48:46 +00:00
parent 6aa3e97e25
commit b55b28e657
3 changed files with 26 additions and 2 deletions
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7
ChangeLog
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@ -1,3 +1,10 @@
2016-03-10 Joseph Myers <joseph@codesourcery.com>
* manual/math.texi (Errors in Math Functions): Document relaxed
accuracy goals for IBM long double.
* math/libm-test.inc (test_exceptions): Always allow spurious
"underflow" and "inexact" exceptions for IBM long double.
2016-03-10 H.J. Lu <hongjiu.lu@intel.com>
[BZ #19762]

10
manual/math.texi
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@ -1326,6 +1326,16 @@ interpreted in terms of a fixed-precision 106-bit mantissa, but not
necessarily the exact value actually passed with discontiguous
mantissa bits.
@item
For the IBM @code{long double} format, functions whose results are
fully specified by reference to corresponding IEEE 754 floating-point
operations have the same accuracy goals as other functions, but with
the error bound being the same as that for division (3ulp).
Furthermore, ``inexact'' and ``underflow'' exceptions may be raised
for all functions for any inputs, even where such exceptions are
inconsistent with the returned value, since the underlying
floating-point arithmetic has that property.
@item
Functions behave as if the infinite-precision result computed is zero,
infinity or NaN if and only if that is the mathematically correct

11
math/libm-test.inc
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@ -672,13 +672,20 @@ test_exceptions (const char *test_name, int exception)
test_single_exception (test_name, exception, OVERFLOW_EXCEPTION,
FE_OVERFLOW, "Overflow");
#endif
/* Spurious "underflow" and "inexact" exceptions are always
allowed for IBM long double, in line with the underlying
arithmetic. */
#ifdef FE_UNDERFLOW
if ((exception & UNDERFLOW_EXCEPTION_OK) == 0)
if ((exception & UNDERFLOW_EXCEPTION_OK) == 0
&& !(TEST_COND_ldbl_128ibm
&& (exception & UNDERFLOW_EXCEPTION) == 0))
test_single_exception (test_name, exception, UNDERFLOW_EXCEPTION,
FE_UNDERFLOW, "Underflow");
#endif
#ifdef FE_INEXACT
if ((exception & (INEXACT_EXCEPTION | NO_INEXACT_EXCEPTION)) != 0)
if ((exception & (INEXACT_EXCEPTION | NO_INEXACT_EXCEPTION)) != 0
&& !(TEST_COND_ldbl_128ibm
&& (exception & NO_INEXACT_EXCEPTION) != 0))
test_single_exception (test_name, exception, INEXACT_EXCEPTION,
FE_INEXACT, "Inexact");
#endif