This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Do not allow divide-by-zero exception for pow(+/- 0, -Inf) [committed]
- From: Joseph Myers <joseph at codesourcery dot com>
- To: <libc-alpha at sourceware dot org>
- Date: Wed, 17 Oct 2018 21:24:59 +0000
- Subject: Do not allow divide-by-zero exception for pow(+/- 0, -Inf) [committed]
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.) Committed.
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).
diff --git a/math/libm-test-pow.inc b/math/libm-test-pow.inc
index ff20ad2f04..c7b91c1131 100644
--- a/math/libm-test-pow.inc
+++ b/math/libm-test-pow.inc
@@ -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),
--
Joseph S. Myers
joseph@codesourcery.com