Export of internal Abseil changes

--
97faa5fdfa4cd5d7a74cd9332cddd8a7c1e67b89 by Abseil Team <absl-team@google.com>:

Internal changes

PiperOrigin-RevId: 295164378

--
74990f100b3f4172c770ef8c76c05c8e99febdde by Xiaoyi Zhang <zhangxy@google.com>:

Release `absl::Cord`.

PiperOrigin-RevId: 295161959

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6018c57f43c45c31dc1a61c0cd75fa2aa9be8dab by Gennadiy Rozental <rogeeff@google.com>:

Introduce independent notion of FlagStaticTypeID.

This change separates static flag value type identification from the type specific "vtable" with all the operations specific to value type. This change allows us to do the following:
* We can move most of "vtable" implementation from handle header, which will become public soon, into implementation details of Abseil Flag.
* We can combine back marshalling ops and general ops into a single vtable routine. They were split previously to facilitate type identification without requiring marshalling routines to be exposed in header.
* We do not need to store two vtable pointers. We can now store only one. The static type id can be deduced on request.

Overall we are saving 24 bytes per flag according to size_tester run.

PiperOrigin-RevId: 295149687

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986b78e9ba571aa85154e70bda4580edd45bb7bf by Abseil Team <absl-team@google.com>:

Update internal comments.

PiperOrigin-RevId: 295030681

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825412b29fd6015027bbc3e5f802706eee0d2837 by Matthew Brown <matthewbr@google.com>:

Change str_format_internal::ConversionChar to an enum (from a struct-wrapped enum).

PiperOrigin-RevId: 294987462

--
f9f88d91809d2cc33fc129df70fa93e7a2c35c69 by Derek Mauro <dmauro@google.com>:

Use more precise wording in the question on live-at-head

PiperOrigin-RevId: 294957679
GitOrigin-RevId: 97faa5fdfa4cd5d7a74cd9332cddd8a7c1e67b89
Change-Id: I081e70d148ffac7296d65e2a2f775f643eaf70bf

1 files changed, 1121 insertions, 0 deletions

diff --git a/absl/strings/cord.h b/absl/strings/cord.h
new file mode 100644
index 000000000000..40566cbaa011
--- /dev/null
+++ b/absl/strings/cord.h
@@ -0,0 +1,1121 @@
+// Copyright 2020 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// A Cord is a sequence of characters with some unusual access propreties.
+// A Cord supports efficient insertions and deletions at the start and end of
+// the byte sequence, but random access reads are slower, and random access
+// modifications are not supported by the API.  Cord also provides cheap copies
+// (using a copy-on-write strategy) and cheap substring operations.
+//
+// Thread safety
+// -------------
+// Cord has the same thread-safety properties as many other types like
+// std::string, std::vector<>, int, etc -- it is thread-compatible. In
+// particular, if no thread may call a non-const method, then it is safe to
+// concurrently call const methods. Copying a Cord produces a new instance that
+// can be used concurrently with the original in arbitrary ways.
+//
+// Implementation is similar to the "Ropes" described in:
+//    Ropes: An alternative to strings
+//    Hans J. Boehm, Russ Atkinson, Michael Plass
+//    Software Practice and Experience, December 1995
+
+#ifndef ABSL_STRINGS_CORD_H_
+#define ABSL_STRINGS_CORD_H_
+
+#include <algorithm>
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+#include <iostream>
+#include <iterator>
+#include <string>
+
+#include "absl/base/internal/endian.h"
+#include "absl/base/internal/invoke.h"
+#include "absl/base/internal/per_thread_tls.h"
+#include "absl/base/macros.h"
+#include "absl/base/port.h"
+#include "absl/container/inlined_vector.h"
+#include "absl/functional/function_ref.h"
+#include "absl/meta/type_traits.h"
+#include "absl/strings/internal/cord_internal.h"
+#include "absl/strings/internal/resize_uninitialized.h"
+#include "absl/strings/string_view.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+class Cord;
+class CordTestPeer;
+template <typename Releaser>
+Cord MakeCordFromExternal(absl::string_view, Releaser&&);
+void CopyCordToString(const Cord& src, std::string* dst);
+namespace hash_internal {
+template <typename H>
+H HashFragmentedCord(H, const Cord&);
+}
+
+// A Cord is a sequence of characters.
+class Cord {
+ private:
+  template <typename T>
+  using EnableIfString =
+      absl::enable_if_t<std::is_same<T, std::string>::value, int>;
+
+ public:
+  // --------------------------------------------------------------------
+  // Constructors, destructors and helper factories
+
+  // Create an empty cord
+  constexpr Cord() noexcept;
+
+  // Cord is copyable and efficiently movable.
+  // The moved-from state is valid but unspecified.
+  Cord(const Cord& src);
+  Cord(Cord&& src) noexcept;
+  Cord& operator=(const Cord& x);
+  Cord& operator=(Cord&& x) noexcept;
+
+  // Create a cord out of "src". This constructor is explicit on
+  // purpose so that people do not get automatic type conversions.
+  explicit Cord(absl::string_view src);
+  Cord& operator=(absl::string_view src);
+
+  // These are templated to avoid ambiguities for types that are convertible to
+  // both `absl::string_view` and `std::string`, such as `const char*`.
+  //
+  // Note that these functions reserve the right to reuse the `string&&`'s
+  // memory and that they will do so in the future.
+  template <typename T, EnableIfString<T> = 0>
+  explicit Cord(T&& src) : Cord(absl::string_view(src)) {}
+  template <typename T, EnableIfString<T> = 0>
+  Cord& operator=(T&& src);
+
+  // Destroy the cord
+  ~Cord() {
+    if (contents_.is_tree()) DestroyCordSlow();
+  }
+
+  // Creates a Cord that takes ownership of external memory. The contents of
+  // `data` are not copied.
+  //
+  // This function takes a callable that is invoked when all Cords are
+  // finished with `data`. The data must remain live and unchanging until the
+  // releaser is called. The requirements for the releaser are that it:
+  //   * is move constructible,
+  //   * supports `void operator()(absl::string_view) const`,
+  //   * does not have alignment requirement greater than what is guaranteed by
+  //     ::operator new. This is dictated by alignof(std::max_align_t) before
+  //     C++17 and __STDCPP_DEFAULT_NEW_ALIGNMENT__ if compiling with C++17 or
+  //     it is supported by the implementation.
+  //
+  // Example:
+  //
+  // Cord MakeCord(BlockPool* pool) {
+  //   Block* block = pool->NewBlock();
+  //   FillBlock(block);
+  //   return absl::MakeCordFromExternal(
+  //       block->ToStringView(),
+  //       [pool, block](absl::string_view /*ignored*/) {
+  //         pool->FreeBlock(block);
+  //       });
+  // }
+  //
+  // WARNING: It's likely a bug if your releaser doesn't do anything.
+  // For example, consider the following:
+  //
+  // void Foo(const char* buffer, int len) {
+  //   auto c = absl::MakeCordFromExternal(absl::string_view(buffer, len),
+  //                                       [](absl::string_view) {});
+  //
+  //   // BUG: If Bar() copies its cord for any reason, including keeping a
+  //   // substring of it, the lifetime of buffer might be extended beyond
+  //   // when Foo() returns.
+  //   Bar(c);
+  // }
+  template <typename Releaser>
+  friend Cord MakeCordFromExternal(absl::string_view data, Releaser&& releaser);
+
+  // --------------------------------------------------------------------
+  // Mutations
+
+  void Clear();
+
+  void Append(const Cord& src);
+  void Append(Cord&& src);
+  void Append(absl::string_view src);
+  template <typename T, EnableIfString<T> = 0>
+  void Append(T&& src);
+
+  void Prepend(const Cord& src);
+  void Prepend(absl::string_view src);
+  template <typename T, EnableIfString<T> = 0>
+  void Prepend(T&& src);
+
+  void RemovePrefix(size_t n);
+  void RemoveSuffix(size_t n);
+
+  // Returns a new cord representing the subrange [pos, pos + new_size) of
+  // *this. If pos >= size(), the result is empty(). If
+  // (pos + new_size) >= size(), the result is the subrange [pos, size()).
+  Cord Subcord(size_t pos, size_t new_size) const;
+
+  friend void swap(Cord& x, Cord& y) noexcept;
+
+  // --------------------------------------------------------------------
+  // Accessors
+
+  size_t size() const;
+  bool empty() const;
+
+  // Returns the approximate number of bytes pinned by this Cord.  Note that
+  // Cords that share memory could each be "charged" independently for the same
+  // shared memory.
+  size_t EstimatedMemoryUsage() const;
+
+  // --------------------------------------------------------------------
+  // Comparators
+
+  // Compares 'this' Cord with rhs. This function and its relatives
+  // treat Cords as sequences of unsigned bytes. The comparison is a
+  // straightforward lexicographic comparison. Return value:
+  //   -1  'this' Cord is smaller
+  //    0  two Cords are equal
+  //    1  'this' Cord is larger
+  int Compare(absl::string_view rhs) const;
+  int Compare(const Cord& rhs) const;
+
+  // Does 'this' cord start/end with rhs
+  bool StartsWith(const Cord& rhs) const;
+  bool StartsWith(absl::string_view rhs) const;
+  bool EndsWith(absl::string_view rhs) const;
+  bool EndsWith(const Cord& rhs) const;
+
+  // --------------------------------------------------------------------
+  // Conversion to other types
+
+  explicit operator std::string() const;
+
+  // Copies the contents from `src` to `*dst`.
+  //
+  // This function optimizes the case of reusing the destination std::string since it
+  // can reuse previously allocated capacity. However, this function does not
+  // guarantee that pointers previously returned by `dst->data()` remain valid
+  // even if `*dst` had enough capacity to hold `src`. If `*dst` is a new
+  // object, prefer to simply use the conversion operator to `std::string`.
+  friend void CopyCordToString(const Cord& src, std::string* dst);
+
+  // --------------------------------------------------------------------
+  // Iteration
+
+  class CharIterator;
+
+  // Type for iterating over the chunks of a `Cord`. See comments for
+  // `Cord::chunk_begin()`, `Cord::chunk_end()` and `Cord::Chunks()` below for
+  // preferred usage.
+  //
+  // Additional notes:
+  //   * The `string_view` returned by dereferencing a valid, non-`end()`
+  //     iterator is guaranteed to be non-empty.
+  //   * A `ChunkIterator` object is invalidated after any non-const
+  //     operation on the `Cord` object over which it iterates.
+  //   * Two `ChunkIterator` objects can be equality compared if and only if
+  //     they remain valid and iterate over the same `Cord`.
+  //   * This is a proxy iterator. This means the `string_view` returned by the
+  //     iterator does not live inside the Cord, and its lifetime is limited to
+  //     the lifetime of the iterator itself. To help prevent issues,
+  //     `ChunkIterator::reference` is not a true reference type and is
+  //     equivalent to `value_type`.
+  //   * The iterator keeps state that can grow for `Cord`s that contain many
+  //     nodes and are imbalanced due to sharing. Prefer to pass this type by
+  //     const reference instead of by value.
+  class ChunkIterator {
+   public:
+    using iterator_category = std::input_iterator_tag;
+    using value_type = absl::string_view;
+    using difference_type = ptrdiff_t;
+    using pointer = const value_type*;
+    using reference = value_type;
+
+    ChunkIterator() = default;
+
+    ChunkIterator& operator++();
+    ChunkIterator operator++(int);
+    bool operator==(const ChunkIterator& other) const;
+    bool operator!=(const ChunkIterator& other) const;
+    reference operator*() const;
+    pointer operator->() const;
+
+    friend class Cord;
+    friend class CharIterator;
+
+   private:
+    // Constructs a `begin()` iterator from `cord`.
+    explicit ChunkIterator(const Cord* cord);
+
+    // Removes `n` bytes from `current_chunk_`. Expects `n` to be smaller than
+    // `current_chunk_.size()`.
+    void RemoveChunkPrefix(size_t n);
+    Cord AdvanceAndReadBytes(size_t n);
+    void AdvanceBytes(size_t n);
+    // Iterates `n` bytes, where `n` is expected to be greater than or equal to
+    // `current_chunk_.size()`.
+    void AdvanceBytesSlowPath(size_t n);
+
+    // A view into bytes of the current `CordRep`. It may only be a view to a
+    // suffix of bytes if this is being used by `CharIterator`.
+    absl::string_view current_chunk_;
+    // The current leaf, or `nullptr` if the iterator points to short data.
+    // If the current chunk is a substring node, current_leaf_ points to the
+    // underlying flat or external node.
+    absl::cord_internal::CordRep* current_leaf_ = nullptr;
+    // The number of bytes left in the `Cord` over which we are iterating.
+    size_t bytes_remaining_ = 0;
+    absl::InlinedVector<absl::cord_internal::CordRep*, 4>
+        stack_of_right_children_;
+  };
+
+  // Returns an iterator to the first chunk of the `Cord`.
+  //
+  // This is useful for getting a `ChunkIterator` outside the context of a
+  // range-based for-loop (in which case see `Cord::Chunks()` below).
+  //
+  // Example:
+  //
+  //   absl::Cord::ChunkIterator FindAsChunk(const absl::Cord& c,
+  //                                         absl::string_view s) {
+  //     return std::find(c.chunk_begin(), c.chunk_end(), s);
+  //   }
+  ChunkIterator chunk_begin() const;
+  // Returns an iterator one increment past the last chunk of the `Cord`.
+  ChunkIterator chunk_end() const;
+
+  // Convenience wrapper over `Cord::chunk_begin()` and `Cord::chunk_end()` to
+  // enable range-based for-loop iteration over `Cord` chunks.
+  //
+  // Prefer to use `Cord::Chunks()` below instead of constructing this directly.
+  class ChunkRange {
+   public:
+    explicit ChunkRange(const Cord* cord) : cord_(cord) {}
+
+    ChunkIterator begin() const;
+    ChunkIterator end() const;
+
+   private:
+    const Cord* cord_;
+  };
+
+  // Returns a range for iterating over the chunks of a `Cord` with a
+  // range-based for-loop.
+  //
+  // Example:
+  //
+  //   void ProcessChunks(const Cord& cord) {
+  //     for (absl::string_view chunk : cord.Chunks()) { ... }
+  //   }
+  //
+  // Note that the ordinary caveats of temporary lifetime extension apply:
+  //
+  //   void Process() {
+  //     for (absl::string_view chunk : CordFactory().Chunks()) {
+  //       // The temporary Cord returned by CordFactory has been destroyed!
+  //     }
+  //   }
+  ChunkRange Chunks() const;
+
+  // Type for iterating over the characters of a `Cord`. See comments for
+  // `Cord::char_begin()`, `Cord::char_end()` and `Cord::Chars()` below for
+  // preferred usage.
+  //
+  // Additional notes:
+  //   * A `CharIterator` object is invalidated after any non-const
+  //     operation on the `Cord` object over which it iterates.
+  //   * Two `CharIterator` objects can be equality compared if and only if
+  //     they remain valid and iterate over the same `Cord`.
+  //   * The iterator keeps state that can grow for `Cord`s that contain many
+  //     nodes and are imbalanced due to sharing. Prefer to pass this type by
+  //     const reference instead of by value.
+  //   * This type cannot be a forward iterator because a `Cord` can reuse
+  //     sections of memory. This violates the requirement that if dereferencing
+  //     two iterators returns the same object, the iterators must compare
+  //     equal.
+  class CharIterator {
+   public:
+    using iterator_category = std::input_iterator_tag;
+    using value_type = char;
+    using difference_type = ptrdiff_t;
+    using pointer = const char*;
+    using reference = const char&;
+
+    CharIterator() = default;
+
+    CharIterator& operator++();
+    CharIterator operator++(int);
+    bool operator==(const CharIterator& other) const;
+    bool operator!=(const CharIterator& other) const;
+    reference operator*() const;
+    pointer operator->() const;
+
+    friend Cord;
+
+   private:
+    explicit CharIterator(const Cord* cord) : chunk_iterator_(cord) {}
+
+    ChunkIterator chunk_iterator_;
+  };
+
+  // Advances `*it` by `n_bytes` and returns the bytes passed as a `Cord`.
+  //
+  // `n_bytes` must be less than or equal to the number of bytes remaining for
+  // iteration. Otherwise the behavior is undefined. It is valid to pass
+  // `char_end()` and 0.
+  static Cord AdvanceAndRead(CharIterator* it, size_t n_bytes);
+
+  // Advances `*it` by `n_bytes`.
+  //
+  // `n_bytes` must be less than or equal to the number of bytes remaining for
+  // iteration. Otherwise the behavior is undefined. It is valid to pass
+  // `char_end()` and 0.
+  static void Advance(CharIterator* it, size_t n_bytes);
+
+  // Returns the longest contiguous view starting at the iterator's position.
+  //
+  // `it` must be dereferenceable.
+  static absl::string_view ChunkRemaining(const CharIterator& it);
+
+  // Returns an iterator to the first character of the `Cord`.
+  CharIterator char_begin() const;
+  // Returns an iterator to one past the last character of the `Cord`.
+  CharIterator char_end() const;
+
+  // Convenience wrapper over `Cord::char_begin()` and `Cord::char_end()` to
+  // enable range-based for-loop iterator over the characters of a `Cord`.
+  //
+  // Prefer to use `Cord::Chars()` below instead of constructing this directly.
+  class CharRange {
+   public:
+    explicit CharRange(const Cord* cord) : cord_(cord) {}
+
+    CharIterator begin() const;
+    CharIterator end() const;
+
+   private:
+    const Cord* cord_;
+  };
+
+  // Returns a range for iterating over the characters of a `Cord` with a
+  // range-based for-loop.
+  //
+  // Example:
+  //
+  //   void ProcessCord(const Cord& cord) {
+  //     for (char c : cord.Chars()) { ... }
+  //   }
+  //
+  // Note that the ordinary caveats of temporary lifetime extension apply:
+  //
+  //   void Process() {
+  //     for (char c : CordFactory().Chars()) {
+  //       // The temporary Cord returned by CordFactory has been destroyed!
+  //     }
+  //   }
+  CharRange Chars() const;
+
+  // --------------------------------------------------------------------
+  // Miscellaneous
+
+  // Get the "i"th character of 'this' and return it.
+  // NOTE: This routine is reasonably efficient.  It is roughly
+  // logarithmic in the number of nodes that make up the cord.  Still,
+  // if you need to iterate over the contents of a cord, you should
+  // use a CharIterator/CordIterator rather than call operator[] or Get()
+  //  repeatedly in a loop.
+  //
+  // REQUIRES: 0 <= i < size()
+  char operator[](size_t i) const;
+
+  // Flattens the cord into a single array and returns a view of the data.
+  //
+  // If the cord was already flat, the contents are not modified.
+  absl::string_view Flatten();
+
+ private:
+  friend class CordTestPeer;
+  template <typename H>
+  friend H absl::hash_internal::HashFragmentedCord(H, const Cord&);
+  friend bool operator==(const Cord& lhs, const Cord& rhs);
+  friend bool operator==(const Cord& lhs, absl::string_view rhs);
+
+  // Call the provided function once for each cord chunk, in order.  Unlike
+  // Chunks(), this API will not allocate memory.
+  void ForEachChunk(absl::FunctionRef<void(absl::string_view)>) const;
+
+  // Allocates new contiguous storage for the contents of the cord. This is
+  // called by Flatten() when the cord was not already flat.
+  absl::string_view FlattenSlowPath();
+
+  // Actual cord contents are hidden inside the following simple
+  // class so that we can isolate the bulk of cord.cc from changes
+  // to the representation.
+  //
+  // InlineRep holds either either a tree pointer, or an array of kMaxInline
+  // bytes.
+  class InlineRep {
+   public:
+    static const unsigned char kMaxInline = 15;
+    static_assert(kMaxInline >= sizeof(absl::cord_internal::CordRep*), "");
+    // Tag byte & kMaxInline means we are storing a pointer.
+    static const unsigned char kTreeFlag = 1 << 4;
+    // Tag byte & kProfiledFlag means we are profiling the Cord.
+    static const unsigned char kProfiledFlag = 1 << 5;
+
+    constexpr InlineRep() : data_{} {}
+    InlineRep(const InlineRep& src);
+    InlineRep(InlineRep&& src);
+    InlineRep& operator=(const InlineRep& src);
+    InlineRep& operator=(InlineRep&& src) noexcept;
+
+    void Swap(InlineRep* rhs);
+    bool empty() const;
+    size_t size() const;
+    const char* data() const;  // Returns nullptr if holding pointer
+    void set_data(const char* data, size_t n,
+                  bool nullify_tail);  // Discards pointer, if any
+    char* set_data(size_t n);  // Write data to the result
+    // Returns nullptr if holding bytes
+    absl::cord_internal::CordRep* tree() const;
+    // Discards old pointer, if any
+    void set_tree(absl::cord_internal::CordRep* rep);
+    // Replaces a tree with a new root. This is faster than set_tree, but it
+    // should only be used when it's clear that the old rep was a tree.
+    void replace_tree(absl::cord_internal::CordRep* rep);
+    // Returns non-null iff was holding a pointer
+    absl::cord_internal::CordRep* clear();
+    // Convert to pointer if necessary
+    absl::cord_internal::CordRep* force_tree(size_t extra_hint);
+    void reduce_size(size_t n);  // REQUIRES: holding data
+    void remove_prefix(size_t n);  // REQUIRES: holding data
+    void AppendArray(const char* src_data, size_t src_size);
+    absl::string_view FindFlatStartPiece() const;
+    void AppendTree(absl::cord_internal::CordRep* tree);
+    void PrependTree(absl::cord_internal::CordRep* tree);
+    void GetAppendRegion(char** region, size_t* size, size_t max_length);
+    void GetAppendRegion(char** region, size_t* size);
+    bool IsSame(const InlineRep& other) const {
+      return memcmp(data_, other.data_, sizeof(data_)) == 0;
+    }
+    int BitwiseCompare(const InlineRep& other) const {
+      uint64_t x, y;
+      // Use memcpy to avoid anti-aliasing issues.
+      memcpy(&x, data_, sizeof(x));
+      memcpy(&y, other.data_, sizeof(y));
+      if (x == y) {
+        memcpy(&x, data_ + 8, sizeof(x));
+        memcpy(&y, other.data_ + 8, sizeof(y));
+        if (x == y) return 0;
+      }
+      return absl::big_endian::FromHost64(x) < absl::big_endian::FromHost64(y)
+                 ? -1
+                 : 1;
+    }
+    void CopyTo(std::string* dst) const {
+      // memcpy is much faster when operating on a known size. On most supported
+      // platforms, the small std::string optimization is large enough that resizing
+      // to 15 bytes does not cause a memory allocation.
+      absl::strings_internal::STLStringResizeUninitialized(dst,
+                                                           sizeof(data_) - 1);
+      memcpy(&(*dst)[0], data_, sizeof(data_) - 1);
+      // erase is faster than resize because the logic for memory allocation is
+      // not needed.
+      dst->erase(data_[kMaxInline]);
+    }
+
+    // Copies the inline contents into `dst`. Assumes the cord is not empty.
+    void CopyToArray(char* dst) const;
+
+    bool is_tree() const { return data_[kMaxInline] > kMaxInline; }
+
+   private:
+    friend class Cord;
+
+    void AssignSlow(const InlineRep& src);
+    // Unrefs the tree, stops profiling, and zeroes the contents
+    void ClearSlow();
+
+    // If the data has length <= kMaxInline, we store it in data_[0..len-1],
+    // and store the length in data_[kMaxInline].  Else we store it in a tree
+    // and store a pointer to that tree in data_[0..sizeof(CordRep*)-1].
+    alignas(absl::cord_internal::CordRep*) char data_[kMaxInline + 1];
+  };
+  InlineRep contents_;
+
+  // Helper for MemoryUsage()
+  static size_t MemoryUsageAux(const absl::cord_internal::CordRep* rep);
+
+  // Helper for GetFlat()
+  static bool GetFlatAux(absl::cord_internal::CordRep* rep,
+                         absl::string_view* fragment);
+
+  // Helper for ForEachChunk()
+  static void ForEachChunkAux(
+      absl::cord_internal::CordRep* rep,
+      absl::FunctionRef<void(absl::string_view)> callback);
+
+  // The destructor for non-empty Cords.
+  void DestroyCordSlow();
+
+  // Out-of-line implementation of slower parts of logic.
+  void CopyToArraySlowPath(char* dst) const;
+  int CompareSlowPath(absl::string_view rhs, size_t compared_size,
+                      size_t size_to_compare) const;
+  int CompareSlowPath(const Cord& rhs, size_t compared_size,
+                      size_t size_to_compare) const;
+  bool EqualsImpl(absl::string_view rhs, size_t size_to_compare) const;
+  bool EqualsImpl(const Cord& rhs, size_t size_to_compare) const;
+  int CompareImpl(const Cord& rhs) const;
+
+  template <typename ResultType, typename RHS>
+  friend ResultType GenericCompare(const Cord& lhs, const RHS& rhs,
+                                   size_t size_to_compare);
+  static absl::string_view GetFirstChunk(const Cord& c);
+  static absl::string_view GetFirstChunk(absl::string_view sv);
+
+  // Returns a new reference to contents_.tree(), or steals an existing
+  // reference if called on an rvalue.
+  absl::cord_internal::CordRep* TakeRep() const&;
+  absl::cord_internal::CordRep* TakeRep() &&;
+
+  // Helper for Append()
+  template <typename C>
+  void AppendImpl(C&& src);
+};
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// allow a Cord to be logged
+extern std::ostream& operator<<(std::ostream& out, const Cord& cord);
+
+// ------------------------------------------------------------------
+// Internal details follow.  Clients should ignore.
+
+namespace cord_internal {
+
+// Fast implementation of memmove for up to 15 bytes. This implementation is
+// safe for overlapping regions. If nullify_tail is true, the destination is
+// padded with '\0' up to 16 bytes.
+inline void SmallMemmove(char* dst, const char* src, size_t n,
+                         bool nullify_tail = false) {
+  if (n >= 8) {
+    assert(n <= 16);
+    uint64_t buf1;
+    uint64_t buf2;
+    memcpy(&buf1, src, 8);
+    memcpy(&buf2, src + n - 8, 8);
+    if (nullify_tail) {
+      memset(dst + 8, 0, 8);
+    }
+    memcpy(dst, &buf1, 8);
+    memcpy(dst + n - 8, &buf2, 8);
+  } else if (n >= 4) {
+    uint32_t buf1;
+    uint32_t buf2;
+    memcpy(&buf1, src, 4);
+    memcpy(&buf2, src + n - 4, 4);
+    if (nullify_tail) {
+      memset(dst + 4, 0, 4);
+      memset(dst + 8, 0, 8);
+    }
+    memcpy(dst, &buf1, 4);
+    memcpy(dst + n - 4, &buf2, 4);
+  } else {
+    if (n != 0) {
+      dst[0] = src[0];
+      dst[n / 2] = src[n / 2];
+      dst[n - 1] = src[n - 1];
+    }
+    if (nullify_tail) {
+      memset(dst + 8, 0, 8);
+      memset(dst + n, 0, 8);
+    }
+  }
+}
+
+struct ExternalRepReleaserPair {
+  CordRep* rep;
+  void* releaser_address;
+};
+
+// Allocates a new external `CordRep` and returns a pointer to it and a pointer
+// to `releaser_size` bytes where the desired releaser can be constructed.
+// Expects `data` to be non-empty.
+ExternalRepReleaserPair NewExternalWithUninitializedReleaser(
+    absl::string_view data, ExternalReleaserInvoker invoker,
+    size_t releaser_size);
+
+// Creates a new `CordRep` that owns `data` and `releaser` and returns a pointer
+// to it, or `nullptr` if `data` was empty.
+template <typename Releaser>
+// NOLINTNEXTLINE - suppress clang-tidy raw pointer return.
+CordRep* NewExternalRep(absl::string_view data, Releaser&& releaser) {
+  static_assert(
+#if defined(__STDCPP_DEFAULT_NEW_ALIGNMENT__)
+      alignof(Releaser) <= __STDCPP_DEFAULT_NEW_ALIGNMENT__,
+#else
+      alignof(Releaser) <= alignof(max_align_t),
+#endif
+      "Releasers with alignment requirement greater than what is returned by "
+      "default `::operator new()` are not supported.");
+
+  using ReleaserType = absl::decay_t<Releaser>;
+  if (data.empty()) {
+    // Never create empty external nodes.
+    ::absl::base_internal::Invoke(
+        ReleaserType(std::forward<Releaser>(releaser)), data);
+    return nullptr;
+  }
+
+  auto releaser_invoker = [](void* type_erased_releaser, absl::string_view d) {
+    auto* my_releaser = static_cast<ReleaserType*>(type_erased_releaser);
+    ::absl::base_internal::Invoke(std::move(*my_releaser), d);
+    my_releaser->~ReleaserType();
+    return sizeof(Releaser);
+  };
+
+  ExternalRepReleaserPair external = NewExternalWithUninitializedReleaser(
+      data, releaser_invoker, sizeof(releaser));
+  ::new (external.releaser_address)
+      ReleaserType(std::forward<Releaser>(releaser));
+  return external.rep;
+}
+
+// Overload for function reference types that dispatches using a function
+// pointer because there are no `alignof()` or `sizeof()` a function reference.
+// NOLINTNEXTLINE - suppress clang-tidy raw pointer return.
+inline CordRep* NewExternalRep(absl::string_view data,
+                               void (&releaser)(absl::string_view)) {
+  return NewExternalRep(data, &releaser);
+}
+
+}  // namespace cord_internal
+
+template <typename Releaser>
+Cord MakeCordFromExternal(absl::string_view data, Releaser&& releaser) {
+  Cord cord;
+  cord.contents_.set_tree(::absl::cord_internal::NewExternalRep(
+      data, std::forward<Releaser>(releaser)));
+  return cord;
+}
+
+inline Cord::InlineRep::InlineRep(const Cord::InlineRep& src) {
+  cord_internal::SmallMemmove(data_, src.data_, sizeof(data_));
+}
+
+inline Cord::InlineRep::InlineRep(Cord::InlineRep&& src) {
+  memcpy(data_, src.data_, sizeof(data_));
+  memset(src.data_, 0, sizeof(data_));
+}
+
+inline Cord::InlineRep& Cord::InlineRep::operator=(const Cord::InlineRep& src) {
+  if (this == &src) {
+    return *this;
+  }
+  if (!is_tree() && !src.is_tree()) {
+    cord_internal::SmallMemmove(data_, src.data_, sizeof(data_));
+    return *this;
+  }
+  AssignSlow(src);
+  return *this;
+}
+
+inline Cord::InlineRep& Cord::InlineRep::operator=(
+    Cord::InlineRep&& src) noexcept {
+  if (is_tree()) {
+    ClearSlow();
+  }
+  memcpy(data_, src.data_, sizeof(data_));
+  memset(src.data_, 0, sizeof(data_));
+  return *this;
+}
+
+inline void Cord::InlineRep::Swap(Cord::InlineRep* rhs) {
+  if (rhs == this) {
+    return;
+  }
+
+  Cord::InlineRep tmp;
+  cord_internal::SmallMemmove(tmp.data_, data_, sizeof(data_));
+  cord_internal::SmallMemmove(data_, rhs->data_, sizeof(data_));
+  cord_internal::SmallMemmove(rhs->data_, tmp.data_, sizeof(data_));
+}
+
+inline const char* Cord::InlineRep::data() const {
+  return is_tree() ? nullptr : data_;
+}
+
+inline absl::cord_internal::CordRep* Cord::InlineRep::tree() const {
+  if (is_tree()) {
+    absl::cord_internal::CordRep* rep;
+    memcpy(&rep, data_, sizeof(rep));
+    return rep;
+  } else {
+    return nullptr;
+  }
+}
+
+inline bool Cord::InlineRep::empty() const { return data_[kMaxInline] == 0; }
+
+inline size_t Cord::InlineRep::size() const {
+  const char tag = data_[kMaxInline];
+  if (tag <= kMaxInline) return tag;
+  return static_cast<size_t>(tree()->length);
+}
+
+inline void Cord::InlineRep::set_tree(absl::cord_internal::CordRep* rep) {
+  if (rep == nullptr) {
+    memset(data_, 0, sizeof(data_));
+  } else {
+    bool was_tree = is_tree();
+    memcpy(data_, &rep, sizeof(rep));
+    memset(data_ + sizeof(rep), 0, sizeof(data_) - sizeof(rep) - 1);
+    if (!was_tree) {
+      data_[kMaxInline] = kTreeFlag;
+    }
+  }
+}
+
+inline void Cord::InlineRep::replace_tree(absl::cord_internal::CordRep* rep) {
+  ABSL_ASSERT(is_tree());
+  if (ABSL_PREDICT_FALSE(rep == nullptr)) {
+    set_tree(rep);
+    return;
+  }
+  memcpy(data_, &rep, sizeof(rep));
+  memset(data_ + sizeof(rep), 0, sizeof(data_) - sizeof(rep) - 1);
+}
+
+inline absl::cord_internal::CordRep* Cord::InlineRep::clear() {
+  const char tag = data_[kMaxInline];
+  absl::cord_internal::CordRep* result = nullptr;
+  if (tag > kMaxInline) {
+    memcpy(&result, data_, sizeof(result));
+  }
+  memset(data_, 0, sizeof(data_));  // Clear the cord
+  return result;
+}
+
+inline void Cord::InlineRep::CopyToArray(char* dst) const {
+  assert(!is_tree());
+  size_t n = data_[kMaxInline];
+  assert(n != 0);
+  cord_internal::SmallMemmove(dst, data_, n);
+}
+
+constexpr inline Cord::Cord() noexcept {}
+
+inline Cord& Cord::operator=(const Cord& x) {
+  contents_ = x.contents_;
+  return *this;
+}
+
+inline Cord::Cord(Cord&& src) noexcept : contents_(std::move(src.contents_)) {}
+
+inline Cord& Cord::operator=(Cord&& x) noexcept {
+  contents_ = std::move(x.contents_);
+  return *this;
+}
+
+template <typename T, Cord::EnableIfString<T>>
+inline Cord& Cord::operator=(T&& src) {
+  *this = absl::string_view(src);
+  return *this;
+}
+
+inline size_t Cord::size() const {
+  // Length is 1st field in str.rep_
+  return contents_.size();
+}
+
+inline bool Cord::empty() const { return contents_.empty(); }
+
+inline size_t Cord::EstimatedMemoryUsage() const {
+  size_t result = sizeof(Cord);
+  if (const absl::cord_internal::CordRep* rep = contents_.tree()) {
+    result += MemoryUsageAux(rep);
+  }
+  return result;
+}
+
+inline absl::string_view Cord::Flatten() {
+  absl::cord_internal::CordRep* rep = contents_.tree();
+  if (rep == nullptr) {
+    return absl::string_view(contents_.data(), contents_.size());
+  } else {
+    absl::string_view already_flat_contents;
+    if (GetFlatAux(rep, &already_flat_contents)) {
+      return already_flat_contents;
+    }
+  }
+  return FlattenSlowPath();
+}
+
+inline void Cord::Append(absl::string_view src) {
+  contents_.AppendArray(src.data(), src.size());
+}
+
+template <typename T, Cord::EnableIfString<T>>
+inline void Cord::Append(T&& src) {
+  // Note that this function reserves the right to reuse the `string&&`'s
+  // memory and that it will do so in the future.
+  Append(absl::string_view(src));
+}
+
+template <typename T, Cord::EnableIfString<T>>
+inline void Cord::Prepend(T&& src) {
+  // Note that this function reserves the right to reuse the `string&&`'s
+  // memory and that it will do so in the future.
+  Prepend(absl::string_view(src));
+}
+
+inline int Cord::Compare(const Cord& rhs) const {
+  if (!contents_.is_tree() && !rhs.contents_.is_tree()) {
+    return contents_.BitwiseCompare(rhs.contents_);
+  }
+
+  return CompareImpl(rhs);
+}
+
+// Does 'this' cord start/end with rhs
+inline bool Cord::StartsWith(const Cord& rhs) const {
+  if (contents_.IsSame(rhs.contents_)) return true;
+  size_t rhs_size = rhs.size();
+  if (size() < rhs_size) return false;
+  return EqualsImpl(rhs, rhs_size);
+}
+
+inline bool Cord::StartsWith(absl::string_view rhs) const {
+  size_t rhs_size = rhs.size();
+  if (size() < rhs_size) return false;
+  return EqualsImpl(rhs, rhs_size);
+}
+
+inline Cord::ChunkIterator::ChunkIterator(const Cord* cord)
+    : bytes_remaining_(cord->size()) {
+  if (cord->empty()) return;
+  if (cord->contents_.is_tree()) {
+    stack_of_right_children_.push_back(cord->contents_.tree());
+    operator++();
+  } else {
+    current_chunk_ = absl::string_view(cord->contents_.data(), cord->size());
+  }
+}
+
+inline Cord::ChunkIterator Cord::ChunkIterator::operator++(int) {
+  ChunkIterator tmp(*this);
+  operator++();
+  return tmp;
+}
+
+inline bool Cord::ChunkIterator::operator==(const ChunkIterator& other) const {
+  return bytes_remaining_ == other.bytes_remaining_;
+}
+
+inline bool Cord::ChunkIterator::operator!=(const ChunkIterator& other) const {
+  return !(*this == other);
+}
+
+inline Cord::ChunkIterator::reference Cord::ChunkIterator::operator*() const {
+  assert(bytes_remaining_ != 0);
+  return current_chunk_;
+}
+
+inline Cord::ChunkIterator::pointer Cord::ChunkIterator::operator->() const {
+  assert(bytes_remaining_ != 0);
+  return &current_chunk_;
+}
+
+inline void Cord::ChunkIterator::RemoveChunkPrefix(size_t n) {
+  assert(n < current_chunk_.size());
+  current_chunk_.remove_prefix(n);
+  bytes_remaining_ -= n;
+}
+
+inline void Cord::ChunkIterator::AdvanceBytes(size_t n) {
+  if (ABSL_PREDICT_TRUE(n < current_chunk_.size())) {
+    RemoveChunkPrefix(n);
+  } else if (n != 0) {
+    AdvanceBytesSlowPath(n);
+  }
+}
+
+inline Cord::ChunkIterator Cord::chunk_begin() const {
+  return ChunkIterator(this);
+}
+
+inline Cord::ChunkIterator Cord::chunk_end() const { return ChunkIterator(); }
+
+inline Cord::ChunkIterator Cord::ChunkRange::begin() const {
+  return cord_->chunk_begin();
+}
+
+inline Cord::ChunkIterator Cord::ChunkRange::end() const {
+  return cord_->chunk_end();
+}
+
+inline Cord::ChunkRange Cord::Chunks() const { return ChunkRange(this); }
+
+inline Cord::CharIterator& Cord::CharIterator::operator++() {
+  if (ABSL_PREDICT_TRUE(chunk_iterator_->size() > 1)) {
+    chunk_iterator_.RemoveChunkPrefix(1);
+  } else {
+    ++chunk_iterator_;
+  }
+  return *this;
+}
+
+inline Cord::CharIterator Cord::CharIterator::operator++(int) {
+  CharIterator tmp(*this);
+  operator++();
+  return tmp;
+}
+
+inline bool Cord::CharIterator::operator==(const CharIterator& other) const {
+  return chunk_iterator_ == other.chunk_iterator_;
+}
+
+inline bool Cord::CharIterator::operator!=(const CharIterator& other) const {
+  return !(*this == other);
+}
+
+inline Cord::CharIterator::reference Cord::CharIterator::operator*() const {
+  return *chunk_iterator_->data();
+}
+
+inline Cord::CharIterator::pointer Cord::CharIterator::operator->() const {
+  return chunk_iterator_->data();
+}
+
+inline Cord Cord::AdvanceAndRead(CharIterator* it, size_t n_bytes) {
+  assert(it != nullptr);
+  return it->chunk_iterator_.AdvanceAndReadBytes(n_bytes);
+}
+
+inline void Cord::Advance(CharIterator* it, size_t n_bytes) {
+  assert(it != nullptr);
+  it->chunk_iterator_.AdvanceBytes(n_bytes);
+}
+
+inline absl::string_view Cord::ChunkRemaining(const CharIterator& it) {
+  return *it.chunk_iterator_;
+}
+
+inline Cord::CharIterator Cord::char_begin() const {
+  return CharIterator(this);
+}
+
+inline Cord::CharIterator Cord::char_end() const { return CharIterator(); }
+
+inline Cord::CharIterator Cord::CharRange::begin() const {
+  return cord_->char_begin();
+}
+
+inline Cord::CharIterator Cord::CharRange::end() const {
+  return cord_->char_end();
+}
+
+inline Cord::CharRange Cord::Chars() const { return CharRange(this); }
+
+inline void Cord::ForEachChunk(
+    absl::FunctionRef<void(absl::string_view)> callback) const {
+  absl::cord_internal::CordRep* rep = contents_.tree();
+  if (rep == nullptr) {
+    callback(absl::string_view(contents_.data(), contents_.size()));
+  } else {
+    return ForEachChunkAux(rep, callback);
+  }
+}
+
+// Nonmember Cord-to-Cord relational operarators.
+inline bool operator==(const Cord& lhs, const Cord& rhs) {
+  if (lhs.contents_.IsSame(rhs.contents_)) return true;
+  size_t rhs_size = rhs.size();
+  if (lhs.size() != rhs_size) return false;
+  return lhs.EqualsImpl(rhs, rhs_size);
+}
+
+inline bool operator!=(const Cord& x, const Cord& y) { return !(x == y); }
+inline bool operator<(const Cord& x, const Cord& y) {
+  return x.Compare(y) < 0;
+}
+inline bool operator>(const Cord& x, const Cord& y) {
+  return x.Compare(y) > 0;
+}
+inline bool operator<=(const Cord& x, const Cord& y) {
+  return x.Compare(y) <= 0;
+}
+inline bool operator>=(const Cord& x, const Cord& y) {
+  return x.Compare(y) >= 0;
+}
+
+// Nonmember Cord-to-absl::string_view relational operators.
+//
+// Due to implicit conversions, these also enable comparisons of Cord with
+// with std::string, ::string, and const char*.
+inline bool operator==(const Cord& lhs, absl::string_view rhs) {
+  size_t lhs_size = lhs.size();
+  size_t rhs_size = rhs.size();
+  if (lhs_size != rhs_size) return false;
+  return lhs.EqualsImpl(rhs, rhs_size);
+}
+
+inline bool operator==(absl::string_view x, const Cord& y) { return y == x; }
+inline bool operator!=(const Cord& x, absl::string_view y) { return !(x == y); }
+inline bool operator!=(absl::string_view x, const Cord& y) { return !(x == y); }
+inline bool operator<(const Cord& x, absl::string_view y) {
+  return x.Compare(y) < 0;
+}
+inline bool operator<(absl::string_view x, const Cord& y) {
+  return y.Compare(x) > 0;
+}
+inline bool operator>(const Cord& x, absl::string_view y) { return y < x; }
+inline bool operator>(absl::string_view x, const Cord& y) { return y < x; }
+inline bool operator<=(const Cord& x, absl::string_view y) { return !(y < x); }
+inline bool operator<=(absl::string_view x, const Cord& y) { return !(y < x); }
+inline bool operator>=(const Cord& x, absl::string_view y) { return !(x < y); }
+inline bool operator>=(absl::string_view x, const Cord& y) { return !(x < y); }
+
+// Overload of swap for Cord. The use of non-const references is
+// required. :(
+inline void swap(Cord& x, Cord& y) noexcept { y.contents_.Swap(&x.contents_); }
+
+// Some internals exposed to test code.
+namespace strings_internal {
+class CordTestAccess {
+ public:
+  static size_t FlatOverhead();
+  static size_t MaxFlatLength();
+  static size_t SizeofCordRepConcat();
+  static size_t SizeofCordRepExternal();
+  static size_t SizeofCordRepSubstring();
+  static size_t FlatTagToLength(uint8_t tag);
+  static uint8_t LengthToTag(size_t s);
+};
+}  // namespace strings_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_CORD_H_