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<bit>: Improve has_single_bit() codegen #5367

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Merged
merged 7 commits into from
Apr 10, 2025
Merged

<bit>: Improve has_single_bit() codegen #5367

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365b42a
<bit>: Improve std::has_single_bit
pps83 Mar 27, 2025
59a62b8
Keep old code for 32-bit x86 (30% faster)
pps83 Mar 27, 2025
b96db7a
Add has_single_bit benchmark
pps83 Mar 27, 2025
f546b3b
update
pps83 Mar 27, 2025
14656fc
test 1 per iteration
pps83 Mar 27, 2025
283c320
Code review feedback.
StephanTLavavej Apr 1, 2025
eddb362
Avoid shadowing.
StephanTLavavej Apr 9, 2025
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2 changes: 1 addition & 1 deletion stl/inc/bit
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Original file line number Diff line number Diff line change
Expand Up @@ -84,7 +84,7 @@ _NODISCARD constexpr int countl_zero(_Ty _Val) noexcept;

_EXPORT_STD template <_Standard_unsigned_integral _Ty>
_NODISCARD constexpr bool has_single_bit(const _Ty _Val) noexcept {
return _Val != 0 && (_Val & (_Val - 1)) == 0;
return (_Val ^ (_Val - 1)) > _Val - 1;
}

inline void _Precondition_violation_in_bit_ceil() noexcept {}
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