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Message-ID: <20160823194752.GH1280@port70.net>
Date: Tue, 23 Aug 2016 21:47:53 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Cc: Roland McGrath <mcgrathr@...gle.com>
Subject: [PATCH] math: fix 128bit long double inverse trigonometric functions
there was a copy paste error that could cause large ulp errors
in atan2l, atanl, asinl and acosl on aarch64, mips64 and mipsn32.
(the implementation is from freebsd fdlibm, but the tail end
of the polynomial was wrong. 128 bit long double functions
are not yet tested so this went undetected.)
---
this was found by the change
https://fuchsia.googlesource.com/magenta/+/5fd5aa1b2e567f6b6633fc84ea84443b496f7eb6%5E%21
i tested manually at a few inputs that the patch is sound,
the bug did not cause completely wrong results, the first
couple bits were fine since the leading coefficients were
correct.
src/math/__invtrigl.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/math/__invtrigl.c b/src/math/__invtrigl.c
index ef7f4e1..48f83aa 100644
--- a/src/math/__invtrigl.c
+++ b/src/math/__invtrigl.c
@@ -57,7 +57,7 @@ long double __invtrigl_R(long double z)
{
long double p, q;
p = z*(pS0+z*(pS1+z*(pS2+z*(pS3+z*(pS4+z*(pS5+z*(pS6+z*(pS7+z*(pS8+z*pS9)))))))));
- q = 1.0+z*(qS1+z*(qS2+z*(qS3+z*(qS4+z*(qS5+z*(pS6+z*(pS7+z*(pS8+z*pS9))))))));
+ q = 1.0+z*(qS1+z*(qS2+z*(qS3+z*(qS4+z*(qS5+z*(qS6+z*(qS7+z*(qS8+z*qS9))))))));
return p/q;
}
#endif
--
2.8.1
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