diff options
Diffstat (limited to 'absl/hash/internal/hash.h')
| -rw-r--r-- | absl/hash/internal/hash.h | 135 |
1 files changed, 56 insertions, 79 deletions
diff --git a/absl/hash/internal/hash.h b/absl/hash/internal/hash.h index 025d287f39c9..a71bd4a65df8 100644 --- a/absl/hash/internal/hash.h +++ b/absl/hash/internal/hash.h @@ -43,7 +43,6 @@ #include "absl/container/fixed_array.h" #include "absl/meta/type_traits.h" #include "absl/numeric/int128.h" -#include "absl/strings/cord.h" #include "absl/strings/string_view.h" #include "absl/types/optional.h" #include "absl/types/variant.h" @@ -54,12 +53,65 @@ namespace absl { ABSL_NAMESPACE_BEGIN namespace hash_internal { -class PiecewiseCombiner; - // Internal detail: Large buffers are hashed in smaller chunks. This function // returns the size of these chunks. constexpr size_t PiecewiseChunkSize() { return 1024; } +// PiecewiseCombiner +// +// PiecewiseCombiner is an internal-only helper class for hashing a piecewise +// buffer of `char` or `unsigned char` as though it were contiguous. This class +// provides two methods: +// +// H add_buffer(state, data, size) +// H finalize(state) +// +// `add_buffer` can be called zero or more times, followed by a single call to +// `finalize`. This will produce the same hash expansion as concatenating each +// buffer piece into a single contiguous buffer, and passing this to +// `H::combine_contiguous`. +// +// Example usage: +// PiecewiseCombiner combiner; +// for (const auto& piece : pieces) { +// state = combiner.add_buffer(std::move(state), piece.data, piece.size); +// } +// return combiner.finalize(std::move(state)); +class PiecewiseCombiner { + public: + PiecewiseCombiner() : position_(0) {} + PiecewiseCombiner(const PiecewiseCombiner&) = delete; + PiecewiseCombiner& operator=(const PiecewiseCombiner&) = delete; + + // PiecewiseCombiner::add_buffer() + // + // Appends the given range of bytes to the sequence to be hashed, which may + // modify the provided hash state. + template <typename H> + H add_buffer(H state, const unsigned char* data, size_t size); + template <typename H> + H add_buffer(H state, const char* data, size_t size) { + return add_buffer(std::move(state), + reinterpret_cast<const unsigned char*>(data), size); + } + + // PiecewiseCombiner::finalize() + // + // Finishes combining the hash sequence, which may may modify the provided + // hash state. + // + // Once finalize() is called, add_buffer() may no longer be called. The + // resulting hash state will be the same as if the pieces passed to + // add_buffer() were concatenated into a single flat buffer, and then provided + // to H::combine_contiguous(). + template <typename H> + H finalize(H state); + + private: + unsigned char buf_[PiecewiseChunkSize()]; + size_t position_; +}; + // HashStateBase // // A hash state object represents an intermediate state in the computation @@ -126,8 +178,7 @@ class HashStateBase { template <typename T> static H combine_contiguous(H state, const T* data, size_t size); - private: - friend class PiecewiseCombiner; + using AbslInternalPiecewiseCombiner = PiecewiseCombiner; }; // is_uniquely_represented @@ -198,61 +249,6 @@ H hash_bytes(H hash_state, const T& value) { return H::combine_contiguous(std::move(hash_state), start, sizeof(value)); } -// PiecewiseCombiner -// -// PiecewiseCombiner is an internal-only helper class for hashing a piecewise -// buffer of `char` or `unsigned char` as though it were contiguous. This class -// provides two methods: -// -// H add_buffer(state, data, size) -// H finalize(state) -// -// `add_buffer` can be called zero or more times, followed by a single call to -// `finalize`. This will produce the same hash expansion as concatenating each -// buffer piece into a single contiguous buffer, and passing this to -// `H::combine_contiguous`. -// -// Example usage: -// PiecewiseCombiner combiner; -// for (const auto& piece : pieces) { -// state = combiner.add_buffer(std::move(state), piece.data, piece.size); -// } -// return combiner.finalize(std::move(state)); -class PiecewiseCombiner { - public: - PiecewiseCombiner() : position_(0) {} - PiecewiseCombiner(const PiecewiseCombiner&) = delete; - PiecewiseCombiner& operator=(const PiecewiseCombiner&) = delete; - - // PiecewiseCombiner::add_buffer() - // - // Appends the given range of bytes to the sequence to be hashed, which may - // modify the provided hash state. - template <typename H> - H add_buffer(H state, const unsigned char* data, size_t size); - template <typename H> - H add_buffer(H state, const char* data, size_t size) { - return add_buffer(std::move(state), - reinterpret_cast<const unsigned char*>(data), size); - } - - // PiecewiseCombiner::finalize() - // - // Finishes combining the hash sequence, which may may modify the provided - // hash state. - // - // Once finalize() is called, add_buffer() may no longer be called. The - // resulting hash state will be the same as if the pieces passed to - // add_buffer() were concatenated into a single flat buffer, and then provided - // to H::combine_contiguous(). - template <typename H> - H finalize(H state); - - private: - unsigned char buf_[PiecewiseChunkSize()]; - size_t position_; -}; - // ----------------------------------------------------------------------------- // AbslHashValue for Basic Types // ----------------------------------------------------------------------------- @@ -443,25 +439,6 @@ H AbslHashValue( str.size()); } -template <typename H> -H HashFragmentedCord(H hash_state, const absl::Cord& c) { - PiecewiseCombiner combiner; - c.ForEachChunk([&combiner, &hash_state](absl::string_view chunk) { - hash_state = - combiner.add_buffer(std::move(hash_state), chunk.data(), chunk.size()); - }); - return H::combine(combiner.finalize(std::move(hash_state)), c.size()); -} - -template <typename H> -H AbslHashValue(H hash_state, const absl::Cord& c) { - absl::optional<absl::string_view> maybe_flat = c.TryFlat(); - if (maybe_flat.has_value()) { - return H::combine(std::move(hash_state), *maybe_flat); - } - return hash_internal::HashFragmentedCord(std::move(hash_state), c); -} - // ----------------------------------------------------------------------------- // AbslHashValue for Sequence Containers // ----------------------------------------------------------------------------- |