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Date: Fri, 18 Aug 2023 23:16:00 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: Paul Zimmermann <Paul.Zimmermann@...ia.fr>
Cc: musl@...ts.openwall.com
Subject: [PATCH 1/2] math: fix ld80 acoshl(x) for x < 0
acosh(x) is nan for x < 1, but x < 0 cases were not handled specially
and acoshl gave wrong result for some -0x1p32 < x < -2 values, e.g.:
acoshl(-0x1p20) returned -inf,
acoshl(-0x1.4p20) returned -0x1.db365758403aa9acp+0L,
fixed by checking the sign bit and handling it specially.
reported by Paul Zimmermann.
---
src/math/acoshl.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/src/math/acoshl.c b/src/math/acoshl.c
index 8d4b43f6..943cec17 100644
--- a/src/math/acoshl.c
+++ b/src/math/acoshl.c
@@ -10,14 +10,18 @@ long double acoshl(long double x)
long double acoshl(long double x)
{
union ldshape u = {x};
- int e = u.i.se & 0x7fff;
+ int e = u.i.se;
if (e < 0x3fff + 1)
- /* |x| < 2, invalid if x < 1 or nan */
+ /* 0 <= x < 2, invalid if x < 1 */
return log1pl(x-1 + sqrtl((x-1)*(x-1)+2*(x-1)));
if (e < 0x3fff + 32)
- /* |x| < 0x1p32 */
+ /* 2 <= x < 0x1p32 */
return logl(2*x - 1/(x+sqrtl(x*x-1)));
+ if (e & 0x8000)
+ /* x < 0 or x = -0, invalid */
+ return (x - x) / (x - x);
+ /* 0x1p32 <= x or nan */
return logl(x) + 0.693147180559945309417232121458176568L;
}
#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384
--
2.41.0
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