diff options
Diffstat (limited to 'absl/hash/internal/hash.h')
| -rw-r--r-- | absl/hash/internal/hash.h | 53 |
1 files changed, 38 insertions, 15 deletions
diff --git a/absl/hash/internal/hash.h b/absl/hash/internal/hash.h index ccf4cc1a..ef3f3664 100644 --- a/absl/hash/internal/hash.h +++ b/absl/hash/internal/hash.h @@ -56,6 +56,10 @@ #include "absl/types/variant.h" #include "absl/utility/utility.h" +#ifdef ABSL_HAVE_STD_STRING_VIEW +#include <string_view> +#endif + namespace absl { ABSL_NAMESPACE_BEGIN @@ -424,7 +428,7 @@ H AbslHashValue(H hash_state, std::nullptr_t) { // AbslHashValue() for hashing pointers-to-member template <typename H, typename T, typename C> -H AbslHashValue(H hash_state, T C::* ptr) { +H AbslHashValue(H hash_state, T C::*ptr) { auto salient_ptm_size = [](std::size_t n) -> std::size_t { #if defined(_MSC_VER) // Pointers-to-member-function on MSVC consist of one pointer plus 0, 1, 2, @@ -442,8 +446,8 @@ H AbslHashValue(H hash_state, T C::* ptr) { return n == 24 ? 20 : n == 16 ? 12 : n; } #else - // On other platforms, we assume that pointers-to-members do not have - // padding. + // On other platforms, we assume that pointers-to-members do not have + // padding. #ifdef __cpp_lib_has_unique_object_representations static_assert(std::has_unique_object_representations<T C::*>::value); #endif // __cpp_lib_has_unique_object_representations @@ -516,14 +520,15 @@ H AbslHashValue(H hash_state, const std::shared_ptr<T>& ptr) { // the same character sequence. These types are: // // - `absl::Cord` -// - `std::string` (and std::basic_string<char, std::char_traits<char>, A> for -// any allocator A) -// - `absl::string_view` and `std::string_view` +// - `std::string` (and std::basic_string<T, std::char_traits<T>, A> for +// any allocator A and any T in {char, wchar_t, char16_t, char32_t}) +// - `absl::string_view`, `std::string_view`, `std::wstring_view`, +// `std::u16string_view`, and `std::u32_string_view`. // -// For simplicity, we currently support only `char` strings. This support may -// be broadened, if necessary, but with some caution - this overload would -// misbehave in cases where the traits' `eq()` member isn't equivalent to `==` -// on the underlying character type. +// For simplicity, we currently support only strings built on `char`, `wchar_t`, +// `char16_t`, or `char32_t`. This support may be broadened, if necessary, but +// with some caution - this overload would misbehave in cases where the traits' +// `eq()` member isn't equivalent to `==` on the underlying character type. template <typename H> H AbslHashValue(H hash_state, absl::string_view str) { return H::combine( @@ -544,6 +549,21 @@ H AbslHashValue( str.size()); } +#ifdef ABSL_HAVE_STD_STRING_VIEW + +// Support std::wstring_view, std::u16string_view and std::u32string_view. +template <typename Char, typename H, + typename = absl::enable_if_t<std::is_same<Char, wchar_t>::value || + std::is_same<Char, char16_t>::value || + std::is_same<Char, char32_t>::value>> +H AbslHashValue(H hash_state, std::basic_string_view<Char> str) { + return H::combine( + H::combine_contiguous(std::move(hash_state), str.data(), str.size()), + str.size()); +} + +#endif // ABSL_HAVE_STD_STRING_VIEW + // ----------------------------------------------------------------------------- // AbslHashValue for Sequence Containers // ----------------------------------------------------------------------------- @@ -935,8 +955,8 @@ class ABSL_DLL MixingHashState : public HashStateBase<MixingHashState> { #endif // ABSL_HAVE_INTRINSIC_INT128 static constexpr uint64_t kMul = - sizeof(size_t) == 4 ? uint64_t{0xcc9e2d51} - : uint64_t{0x9ddfea08eb382d69}; + sizeof(size_t) == 4 ? uint64_t{0xcc9e2d51} + : uint64_t{0x9ddfea08eb382d69}; template <typename T> using IntegralFastPath = @@ -969,7 +989,8 @@ class ABSL_DLL MixingHashState : public HashStateBase<MixingHashState> { // The result should be the same as running the whole algorithm, but faster. template <typename T, absl::enable_if_t<IntegralFastPath<T>::value, int> = 0> static size_t hash(T value) { - return static_cast<size_t>(Mix(Seed(), static_cast<uint64_t>(value))); + return static_cast<size_t>( + Mix(Seed(), static_cast<std::make_unsigned_t<T>>(value))); } // Overload of MixingHashState::hash() @@ -1073,6 +1094,7 @@ class ABSL_DLL MixingHashState : public HashStateBase<MixingHashState> { // Reads 1 to 3 bytes from p. Zero pads to fill uint32_t. static uint32_t Read1To3(const unsigned char* p, size_t len) { + // The trick used by this implementation is to avoid branches if possible. unsigned char mem0 = p[0]; unsigned char mem1 = p[len / 2]; unsigned char mem2 = p[len - 1]; @@ -1082,7 +1104,7 @@ class ABSL_DLL MixingHashState : public HashStateBase<MixingHashState> { unsigned char significant0 = mem0; #else unsigned char significant2 = mem0; - unsigned char significant1 = mem1; + unsigned char significant1 = len == 2 ? mem0 : mem1; unsigned char significant0 = mem2; #endif return static_cast<uint32_t>(significant0 | // @@ -1135,7 +1157,8 @@ class ABSL_DLL MixingHashState : public HashStateBase<MixingHashState> { // probably per-build and not per-process. ABSL_ATTRIBUTE_ALWAYS_INLINE static uint64_t Seed() { #if (!defined(__clang__) || __clang_major__ > 11) && \ - !defined(__apple_build_version__) + (!defined(__apple_build_version__) || \ + __apple_build_version__ >= 19558921) // Xcode 12 return static_cast<uint64_t>(reinterpret_cast<uintptr_t>(&kSeed)); #else // Workaround the absence of |