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<div class="moz-cite-prefix">On 12/8/2022 10:01 AM, Ludovic Henry
wrote:<br>
</div>
<blockquote type="cite" cite="mid:CADT88DvmACxJCzGMck_ccg704tra5UcCOKH1zmUsDEuszc0Srg@mail.gmail.com">
<div dir="ltr">Hi,
<div><br>
</div>
<div>Yes, this is very much a difference of behavior at the
libm/libc level. I'm trying to figure out whether that
behavior difference is acceptable from the libm/libc level (is
it considered a bug to behave differently across architectures
in that case?). If that behaviour is acceptable in libm/libc,
then is it acceptable to behave differently in Java across
architectures?</div>
<div><br>
</div>
<div>From your answer Palmer, the difference _might_ not be
acceptable in the glibc test suite (I haven't check why the
tests are failing). I'm still trying to figure that one out.</div>
<div><br>
</div>
<div>From your answer Joe, the difference _is_ acceptable from
the documentation. IMO the question becomes whether it's a
case of the implementation details bleeding into the API and
whether we want to be 100% compatible to avoid further issues.
The fix for that could be a simple `RISCV_ONLY(if (isnan(v))
return v);` or equivalent
in src/java.base/share/native/libjava/StrictMath.c to match
the behavior without any extra cost for other platforms.</div>
</div>
</blockquote>
<p><br>
</p>
<p>I would not support changing the library native sources (or Java
sources) in this way to accommodate NaN handling.<br>
</p>
<p>-Joe<br>
</p>
<blockquote type="cite" cite="mid:CADT88DvmACxJCzGMck_ccg704tra5UcCOKH1zmUsDEuszc0Srg@mail.gmail.com">
<div dir="ltr">
<div><br>
</div>
<div>Thanks,</div>
<div>Ludovic</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Thu, Dec 8, 2022 at 2:50 PM
Palmer Dabbelt <<a href="mailto:palmer@dabbelt.com" moz-do-not-send="true" class="moz-txt-link-freetext">palmer@dabbelt.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">On
Thu, 08 Dec 2022 08:26:30 PST (-0800), <a href="mailto:ludovic@rivosinc.com" target="_blank" moz-do-not-send="true" class="moz-txt-link-freetext">ludovic@rivosinc.com</a>
wrote:<br>
> Adding the right address for core-libs-dev.<br>
><br>
> On Thu, Dec 8, 2022 at 12:19 PM Ludovic Henry <<a href="mailto:ludovic@rivosinc.com" target="_blank" moz-do-not-send="true" class="moz-txt-link-freetext">ludovic@rivosinc.com</a>>
wrote:<br>
><br>
>> Hello,<br>
>><br>
>> I've noticed that some Math trigonometry tests are
failing in the GNU<br>
>> Mauve test suite. From digging into it, it's related
to NaN values being<br>
>> passed to java.lang.Math trigonometry functions, and
how these values are<br>
>> handled in the native libm library.<br>
>><br>
>> Given the following C test case compiled and run with
`gcc acos.c -lm &&<br>
>> ./a.out`<br>
>><br>
>> ```<br>
>> #include <stdint.h><br>
>> #include <math.h><br>
>> #include <stdlib.h><br>
>> #include <stdio.h><br>
>><br>
>> void main(int argc, char* argv[]) {<br>
>> int64_t bitsNaN = 0x7fff800000000000L;<br>
>> double valNaN = *((double*)&bitsNaN);<br>
>><br>
>> double resD = acos(valNaN);<br>
>> int64_t res = *((int64_t*)&resD);<br>
>> if (!(res == bitsNaN)) {<br>
>> printf("expected 0x%lx but got 0x%lx\n",
bitsNaN, res);<br>
>> exit(1);<br>
>> }<br>
>> }<br>
>> ```<br>
>><br>
>> On a Linux-x64, the test succeeds, but on
Linux-RISC-V, the test fails.<br>
>><br>
>> You've the same test failure in the equivalent Java
code:<br>
>><br>
>> ```<br>
>> public class acos {<br>
>> public static void main (String[] args) {<br>
>> long bitsNaN = 0x7fff800000000000L;<br>
>> double valNaN =
Double.longBitsToDouble(bitsNaN);<br>
>><br>
>> long res =
Double.doubleToRawLongBits(Math.acos(valNaN));<br>
>> if (!(res == bitsNaN)) {<br>
>> throw new
RuntimeException(String.format("expected 0x%x but<br>
>> got 0x%x", bitsNaN, res));<br>
>> }<br>
>> }<br>
>> }<br>
>> ```<br>
>><br>
>> What approach should we take in these cases? Is it
that the test case is<br>
>> wrong, and should assume that given a NaN, any value
of NaN returned is<br>
>> valid? Or should we make sure that the behavior is
the same across<br>
>> platforms and that we "fix" any difference in
behavior of the native<br>
>> library?<br>
<br>
It might just be a glibc bug, we're failing the acos() tests:
<br>
<a href="https://sourceware.org/glibc/wiki/Release/2.35#RISC-V_.28rv64imafdc.2Flp64d.29" rel="noreferrer" target="_blank" moz-do-not-send="true" class="moz-txt-link-freetext">https://sourceware.org/glibc/wiki/Release/2.35#RISC-V_.28rv64imafdc.2Flp64d.29</a>
<br>
. I haven't looked at why, but they do have some nan-related
bits in <br>
there.<br>
<br>
>><br>
>> Cheers,<br>
>> Ludovic<br>
>><br>
</blockquote>
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