tadeja commented on code in PR #53946:
URL: https://github.com/apache/arrow/pull/53946#discussion_r4432737819
##########
cpp/src/arrow/util/bit_util.h:
##########
@@ -138,20 +138,41 @@ static inline uint64_t TrailingBits(uint64_t v, int
num_bits) {
return (v << n) >> n;
}
-// Returns ceil(log2(x)).
-static inline int Log2(uint64_t x) {
- // DCHECK_GT(x, 0);
+// Returns the number of bits needed to represent x, i.e. std::bit_width(x).
+//
+// 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.
+// 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)
+ return static_cast<int>(std::log2p1(x));
+#else
+ return static_cast<int>(std::bit_width(x));
+#endif
+}
-// TODO: We can remove this condition once CRAN upgrades its macOS
-// SDK from 11.3.
-// __apple_build_version__ should be defined only on Apple clang
+// Returns true if x is a power of two, i.e. std::has_single_bit(x).
+// See the note on BitWidth: the macOS 11.3 SDK only has the pre-standard
+// name std::ispow2.
+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)
- return std::log2p1(x - 1);
+ return std::ispow2(x);
#else
- return std::bit_width(x - 1);
+ return std::has_single_bit(x);
#endif
}
+// Returns ceil(log2(x)).
+static inline int Log2(uint64_t x) {
+ // DCHECK_GT(x, 0);
Review Comment:
nothing here :)
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