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Message-ID: <20191204021045.GA10870@APC301.andestech.com>
Date: Wed, 4 Dec 2019 10:10:45 +0800
From: Ruinland ChuanTzu Tsai <ruinland@...estech.com>
To: <musl@...ts.openwall.com>
CC: <alankao@...estech.com>
Subject: math/powf regression on d28cd0ad commit
Hi musl fellows,
sorry for making the noise again.
Yet I encountered a regression of libc-test's math/powf on x86_64 and
RV64 during the transitions from v1.1.22 to v1.1.23. After bisecting, I
managed to locate the commit that breaks powf() test to be d28cd0ad ,
which introduces a new implementation of powf().
Fail log is shown as follow :
src/math/ucb/powf.h:103: bad fp exception: RU powf(0x1.fffffep+127,0x1p+0)=0x1.fffffep+127, want 0 got INEXACT|OVERFLOW
X src/math/ucb/powf.h:530: bad fp exception: RN powf(0x1.fffff8p-127,0x1p+0)=0x1.fffff8p-127, want 0 got INEXACT|UNDERFLOW
X src/math/ucb/powf.h:533: bad fp exception: RN powf(0x1.fffffcp-127,0x1p+0)=0x1.fffffcp-127, want 0 got INEXACT|UNDERFLOW
X src/math/ucb/powf.h:719: bad fp exception: RN powf(-0x1.fffff8p-127,0x1p+0)=-0x1.fffff8p-127, want 0 got INEXACT|UNDERFLOW
X src/math/ucb/powf.h:722: bad fp exception: RN powf(-0x1.fffffcp-127,0x1p+0)=-0x1.fffffcp-127, want 0 got INEXACT|UNDERFLOW
FAIL ./src/math/powf.exe [status 1]
I took a quick investigation on the RU powf(0x1.fffffep+127,0x1p+0).
In the very end of powf() , a "y", which is a little bit larger than the
expected outcome, gets passed to eval_as_float(). Since we're rounding-
up, it will become an INF, causing the testcase to fail.
It makes me wonder whether the old implementation is safe enough for
someone to revert this change by her/his own ? ( I reverted the change
for testing. It seems to be side-effect free ? )
Best regards,
Ruinland
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