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[libc][math] Fix signed zeros for powf when underflow happens. #112601

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Merged
merged 3 commits into from
Oct 18, 2024
Merged

[libc][math] Fix signed zeros for powf when underflow happens. #112601

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bed5228
[libc][math] Fix signed zeros for powf when underflow happens.
lntue Oct 16, 2024
7b34e70
Address comments.
lntue Oct 18, 2024
e102c0a
Add test for +0.0f underflow output.
lntue Oct 18, 2024
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8 changes: 5 additions & 3 deletions libc/src/math/generic/powf.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -855,9 +855,11 @@ LLVM_LIBC_FUNCTION(float, powf, (float x, float y)) {
: 0.0;
exp2_hi_mid_dd.hi = exp2_hi_mid;

return static_cast<float>(
powf_double_double(idx_x, dx, y6, lo6_hi, exp2_hi_mid_dd)) +
0.0f;
double r_dd = powf_double_double(idx_x, dx, y6, lo6_hi, exp2_hi_mid_dd);
float r_f = static_cast<float>(r_dd);

// Only fix signed zeros for exact zeros results.
return r_dd != 0 ? r_f : r_f + 0.0f;
}

} // namespace LIBC_NAMESPACE_DECL
2 changes: 2 additions & 0 deletions libc/test/src/math/smoke/powf_test.cpp
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Expand Up @@ -190,4 +190,6 @@ TEST_F(LlvmLibcPowfTest, SpecialNumbers) {
FE_UNDERFLOW);
}
}

EXPECT_FP_EQ(-0.0f, LIBC_NAMESPACE::powf(-0.015625f, 25.0f));
}
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