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Do not allow divide-by-zero exception for pow(+/- 0, -Inf).

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C99 wrongly specified a divide-by-zero exception for pow(+/- 0, -Inf);
C11 made it optional after this was pointed out, and the permission
for this exception has been removed in the current C2x draft.  This
patch makes the glibc pow tests reflect the stricter requirement
(which follows the normal IEEE rules that a divide-by-zero exception
is for the case of exact infinite results from *finite* operands, not
for such results when any operand is infinite).

Tested for x86_64 and x86.  (If any other pow implementation in glibc,
not exercised on those architectures, turns out to fail the stricter
test, it should be fixed to avoid the exception in this case.)

	* math/libm-test-pow.inc (pow_test_data): Do not allow
	divide-by-zero exception for pow(+/- 0, -Inf).
This commit is contained in:
Joseph Myers 2018-10-17 21:23:40 +00:00
parent 26756e5756
commit c2b7ccad93
2 changed files with 12 additions and 2 deletions
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5
ChangeLog
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@ -1,3 +1,8 @@
2018-10-17 Joseph Myers <joseph@codesourcery.com>
* math/libm-test-pow.inc (pow_test_data): Do not allow
divide-by-zero exception for pow(+/- 0, -Inf).
2018-10-17 Zack Weinberg <zackw@panix.com>
* manual/job.texi (Job Control is Optional): Remove node, as

9
math/libm-test-pow.inc
View File

@ -248,8 +248,13 @@ static const struct test_ff_f_data pow_test_data[] =
TEST_ff_f (pow, 0, plus_infty, 0, ERRNO_UNCHANGED),
TEST_ff_f (pow, minus_zero, plus_infty, 0, ERRNO_UNCHANGED),
TEST_ff_f (pow, 0, minus_infty, plus_infty, DIVIDE_BY_ZERO_EXCEPTION_OK|ERRNO_UNCHANGED),
TEST_ff_f (pow, minus_zero, minus_infty, plus_infty, DIVIDE_BY_ZERO_EXCEPTION_OK|ERRNO_UNCHANGED),
/* C99 erroneously specified a divide-by-zero exception here,
which is not permitted in C2x (C11 specified it as optional).
See <http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1515.pdf>
and
<http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2271.pdf>. */
TEST_ff_f (pow, 0, minus_infty, plus_infty, ERRNO_UNCHANGED),
TEST_ff_f (pow, minus_zero, minus_infty, plus_infty, ERRNO_UNCHANGED),
/* pow (x, +inf) == +inf for |x| > 1. */
TEST_ff_f (pow, 1.5, plus_infty, plus_infty, ERRNO_UNCHANGED|NO_TEST_INLINE),