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<body><span class="vcard"><a class="email" href="mailto:jfonseca@vmware.com" title="Jose Fonseca <jfonseca@vmware.com>"> <span class="fn">Jose Fonseca</span></a>
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<a class="bz_bug_link
bz_status_NEW "
title="NEW - [llvmpipe] piglit linestipple regression"
href="https://bugs.freedesktop.org/show_bug.cgi?id=96518">bug 96518</a>
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<th>What</th>
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<td>brianp@vmware.com
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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - [llvmpipe] piglit linestipple regression"
href="https://bugs.freedesktop.org/show_bug.cgi?id=96518#c2">Comment # 2</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - [llvmpipe] piglit linestipple regression"
href="https://bugs.freedesktop.org/show_bug.cgi?id=96518">bug 96518</a>
from <span class="vcard"><a class="email" href="mailto:jfonseca@vmware.com" title="Jose Fonseca <jfonseca@vmware.com>"> <span class="fn">Jose Fonseca</span></a>
</span></b>
<pre>Althought generally FMA is more precise, it's possible that it give less
precise results. Especially when dealing with things like whole integers, it's
quite possible that the lower precision of a non-fused MAD ends up "snapping"
things to the right values. Whereas FMA preserves any intermediate rounding
error in the final result.
>From my POV, the issue is either:
- llvmpipe/draw stipple implementation needs better rounding (eg.g,
RoundToNearest as opposed to Truncate)
- the linestipple piglit test needs to be updated to not rely on precise
rounding of the stipple.
Either way I doubt the solution is to avoid FMA.</pre>
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