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Fix ldbl-128/ldbl-128ibm lgamma spurious "invalid", incorrect signgam (bug 18952) [committed]
- From: Joseph Myers <joseph at codesourcery dot com>
- To: <libc-alpha at sourceware dot org>
- Date: Fri, 11 Sep 2015 15:35:04 +0000
- Subject: Fix ldbl-128/ldbl-128ibm lgamma spurious "invalid", incorrect signgam (bug 18952) [committed]
- Authentication-results: sourceware.org; auth=none
The ldbl-128 / ldbl-128ibm implementation of lgammal converts (the
floor of minus) non-integer negative arguments to int to determine the
value of signgam. When those values are outside the range of int,
this produces spurious "invalid" exceptions and incorrect values of
signgam. This patch fixes this by instead determining signgam through
comparing half the integer in question to floor of half the integer.
Tested for mips64, x86_64 and x86. Committed.
(auto-libm-test-out diffs omitted below.)
2015-09-11 Joseph Myers <joseph@codesourcery.com>
[BZ #18952]
* sysdeps/ieee754/ldbl-128/e_lgammal_r.c (__ieee754_lgammal_r): Do
not convert non-integer negative arguments to int to determine the
value of signgam.
* math/auto-libm-test-in: Add more tests of lgamma.
* math/auto-libm-test-out: Regenerated.
diff --git a/math/auto-libm-test-in b/math/auto-libm-test-in
index 84b3df0..83eb4cf 100644
--- a/math/auto-libm-test-in
+++ b/math/auto-libm-test-in
@@ -2047,6 +2047,9 @@ lgamma -0xffffffffffffffffp-1
lgamma -0x3ffffffffffffffffffffffffffp-1
lgamma -0x1ffffffffffffffffffffffffffffp-1
+lgamma -0x100000000.8p0
+lgamma -0x100000001.8p0
+
lgamma -0.25
lgamma -0.5
lgamma -0.75
diff --git a/sysdeps/ieee754/ldbl-128/e_lgammal_r.c b/sysdeps/ieee754/ldbl-128/e_lgammal_r.c
index abf0f15..500aacc 100644
--- a/sysdeps/ieee754/ldbl-128/e_lgammal_r.c
+++ b/sysdeps/ieee754/ldbl-128/e_lgammal_r.c
@@ -787,8 +787,8 @@ __ieee754_lgammal_r (long double x, int *signgamp)
p = __floorl (q);
if (p == q)
return (one / (p - p));
- i = p;
- if ((i & 1) == 0)
+ long double halfp = p * 0.5L;
+ if (halfp == __floorl (halfp))
*signgamp = -1;
else
*signgamp = 1;
--
Joseph S. Myers
joseph@codesourcery.com