Export of internal Abseil changes

--
b885a238ec13effcc407e250583e293052bd7984 by Greg Falcon <gfalcon@google.com>:

Remove the dependency of //absl/hash on //absl/strings:cord.

The `AbslHashValue` definition should reside in cord.h, but the implementation currently needs internal details from the hash library.  This CL changes the way that Cord gains access to those internals.  Note that PiecewiseCombiner remains an internal namespace API, and we still reserve the right to make changes to it.

The cord_benchmark shows no statistically significant changes in hash<Cord> performance with this change.

PiperOrigin-RevId: 307393448

--
ca449f230ee719d069d9217ba28a07bf5b3bd8b1 by Derek Mauro <dmauro@google.com>:

Move the extension to use absl::Format() with absl::Cord as a sink to cord.h

PiperOrigin-RevId: 307077162
GitOrigin-RevId: b885a238ec13effcc407e250583e293052bd7984
Change-Id: If24a90782c786fa0b4343bc7d72d053b66c153ea

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
 // -----------------------------------------------------------------------------