Bug fix for associative operations #8839
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Thanks for opening this PR! Could you please add a test case to test/correctness/rfactor.cpp that triggers this? |
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Yes, I have added a test. |
alexreinking
requested changes
Oct 4, 2025
alexreinking
approved these changes
Oct 4, 2025
mcourteaux
reviewed
Oct 13, 2025
| table.emplace_back(select(x0 > tmax_0 - y0, tmax_0, y0), zero_0, true); // Saturating add | ||
| table.emplace_back(select(x0 < -y0, y0, tmax_0), zero_0, true); // Saturating add | ||
| table.emplace_back(select(x0 > tmax_0 - y0, tmax_0, x0 + y0), zero_0, true); // Saturating add | ||
| table.emplace_back(select(x0 < -y0, x0 + y0, tmax_0), zero_0, true); // Saturating add |
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I don't understand this condition: x0 < -y0 doesn't make sense to me with unsigned integer types.
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In uint8, -y0 == 256 - y0 == (255-y0) + 1, which only overflows when y0 is zero, so let's consider that case first. If y0 == 0, x0 < -y0 is always false, so we return 255. That seems wrong. It's fine when y0 != 0
Maybe it's meant to be x0 < ~y0?
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Some of the recognized associative operations for saturating addition return y instead of x + y. This PR fixes that bug.