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GH-49841: [C++] Fix macOS 12.3 SDK build by using __cpp_lib_int_pow2 #50998

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GH-49841: [C++] Fix macOS 12.3 SDK build by using __cpp_lib_int_pow2 #50998

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GH-49841: [C++] Fix macOS 12.3 SDK build by using __cpp_lib_int_pow2
1fanwang Aug 25, 2026
a17e568
Merge remote-tracking branch 'origin/main' into gh-49841-int-pow2-guard
1fanwang Nov 1, 2026
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8 changes: 5 additions & 3 deletions cpp/src/arrow/util/bit_util.h
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Original file line number Diff line number Diff line change
Expand Up @@ -142,12 +142,14 @@ static inline uint64_t TrailingBits(uint64_t v, int num_bits) {
//
// The libc++ in the macOS 11.3 SDK used by CRAN only has the pre-standard
// name std::log2p1. __apple_build_version__ should be defined only on Apple
// clang.
// clang. The macOS 12 SDKs have std::bit_width but leave __cpp_lib_bitops
// undefined, so the check uses __cpp_lib_int_pow2, the feature-test macro for
// std::bit_width and std::has_single_bit.
// TODO: We can remove this condition once CRAN upgrades its macOS SDK from 11.3.
template <typename T>
constexpr int BitWidth(T x) noexcept {
static_assert(std::is_unsigned_v<T>, "BitWidth requires an unsigned integer type");
#if defined(__apple_build_version__) && !defined(__cpp_lib_bitops)
#if defined(__apple_build_version__) && !defined(__cpp_lib_int_pow2)
return static_cast<int>(std::log2p1(x));
#else
return static_cast<int>(std::bit_width(x));
Expand All @@ -160,7 +162,7 @@ constexpr int BitWidth(T x) noexcept {
template <typename T>
constexpr bool HasSingleBit(T x) noexcept {
static_assert(std::is_unsigned_v<T>, "HasSingleBit requires an unsigned integer type");
#if defined(__apple_build_version__) && !defined(__cpp_lib_bitops)
#if defined(__apple_build_version__) && !defined(__cpp_lib_int_pow2)
return std::ispow2(x);
#else
return std::has_single_bit(x);
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