// 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. #include "absl/strings/cord.h" #include <algorithm> #include <atomic> #include <cstddef> #include <cstdio> #include <cstdlib> #include <iomanip> #include <iostream> #include <limits> #include <ostream> #include <sstream> #include <type_traits> #include <unordered_set> #include <vector> #include "absl/base/casts.h" #include "absl/base/internal/raw_logging.h" #include "absl/base/macros.h" #include "absl/base/port.h" #include "absl/container/fixed_array.h" #include "absl/container/inlined_vector.h" #include "absl/strings/escaping.h" #include "absl/strings/internal/cord_internal.h" #include "absl/strings/internal/resize_uninitialized.h" #include "absl/strings/str_cat.h" #include "absl/strings/str_format.h" #include "absl/strings/str_join.h" #include "absl/strings/string_view.h" namespace absl { ABSL_NAMESPACE_BEGIN using ::absl::cord_internal::CordRep; using ::absl::cord_internal::CordRepConcat; using ::absl::cord_internal::CordRepExternal; using ::absl::cord_internal::CordRepSubstring; using ::absl::cord_internal::CONCAT; using ::absl::cord_internal::EXTERNAL; using ::absl::cord_internal::FLAT; using ::absl::cord_internal::SUBSTRING; namespace cord_internal { inline CordRepConcat* CordRep::concat() { assert(tag == CONCAT); return static_cast<CordRepConcat*>(this); } inline const CordRepConcat* CordRep::concat() const { assert(tag == CONCAT); return static_cast<const CordRepConcat*>(this); } inline CordRepSubstring* CordRep::substring() { assert(tag == SUBSTRING); return static_cast<CordRepSubstring*>(this); } inline const CordRepSubstring* CordRep::substring() const { assert(tag == SUBSTRING); return static_cast<const CordRepSubstring*>(this); } inline CordRepExternal* CordRep::external() { assert(tag == EXTERNAL); return static_cast<CordRepExternal*>(this); } inline const CordRepExternal* CordRep::external() const { assert(tag == EXTERNAL); return static_cast<const CordRepExternal*>(this); } } // namespace cord_internal static const size_t kFlatOverhead = offsetof(CordRep, data); // Largest and smallest flat node lengths we are willing to allocate // Flat allocation size is stored in tag, which currently can encode sizes up // to 4K, encoded as multiple of either 8 or 32 bytes. // If we allow for larger sizes, we need to change this to 8/64, 16/128, etc. static constexpr size_t kMaxFlatSize = 4096; static constexpr size_t kMaxFlatLength = kMaxFlatSize - kFlatOverhead; static constexpr size_t kMinFlatLength = 32 - kFlatOverhead; // Prefer copying blocks of at most this size, otherwise reference count. static const size_t kMaxBytesToCopy = 511; // Helper functions for rounded div, and rounding to exact sizes. static size_t DivUp(size_t n, size_t m) { return (n + m - 1) / m; } static size_t RoundUp(size_t n, size_t m) { return DivUp(n, m) * m; } // Returns the size to the nearest equal or larger value that can be // expressed exactly as a tag value. static size_t RoundUpForTag(size_t size) { return RoundUp(size, (size <= 1024) ? 8 : 32); } // Converts the allocated size to a tag, rounding down if the size // does not exactly match a 'tag expressible' size value. The result is // undefined if the size exceeds the maximum size that can be encoded in // a tag, i.e., if size is larger than TagToAllocatedSize(<max tag>). static uint8_t AllocatedSizeToTag(size_t size) { const size_t tag = (size <= 1024) ? size / 8 : 128 + size / 32 - 1024 / 32; assert(tag <= std::numeric_limits<uint8_t>::max()); return tag; } // Converts the provided tag to the corresponding allocated size static constexpr size_t TagToAllocatedSize(uint8_t tag) { return (tag <= 128) ? (tag * 8) : (1024 + (tag - 128) * 32); } // Converts the provided tag to the corresponding available data length static constexpr size_t TagToLength(uint8_t tag) { return TagToAllocatedSize(tag) - kFlatOverhead; } // Enforce that kMaxFlatSize maps to a well-known exact tag value. static_assert(TagToAllocatedSize(224) == kMaxFlatSize, "Bad tag logic"); constexpr uint64_t Fibonacci(unsigned char n, uint64_t a = 0, uint64_t b = 1) { return n == 0 ? a : Fibonacci(n - 1, b, a + b); } static_assert(Fibonacci(63) == 6557470319842, "Fibonacci values computed incorrectly"); // Minimum length required for a given depth tree -- a tree is considered // balanced if // length(t) >= min_length[depth(t)] // The root node depth is allowed to become twice as large to reduce rebalancing // for larger strings (see IsRootBalanced). static constexpr uint64_t min_length[] = { Fibonacci(2), Fibonacci(3), Fibonacci(4), Fibonacci(5), Fibonacci(6), Fibonacci(7), Fibonacci(8), Fibonacci(9), Fibonacci(10), Fibonacci(11), Fibonacci(12), Fibonacci(13), Fibonacci(14), Fibonacci(15), Fibonacci(16), Fibonacci(17), Fibonacci(18), Fibonacci(19), Fibonacci(20), Fibonacci(21), Fibonacci(22), Fibonacci(23), Fibonacci(24), Fibonacci(25), Fibonacci(26), Fibonacci(27), Fibonacci(28), Fibonacci(29), Fibonacci(30), Fibonacci(31), Fibonacci(32), Fibonacci(33), Fibonacci(34), Fibonacci(35), Fibonacci(36), Fibonacci(37), Fibonacci(38), Fibonacci(39), Fibonacci(40), Fibonacci(41), Fibonacci(42), Fibonacci(43), Fibonacci(44), Fibonacci(45), Fibonacci(46), Fibonacci(47), 0xffffffffffffffffull, // Avoid overflow }; static const int kMinLengthSize = ABSL_ARRAYSIZE(min_length); // The inlined size to use with absl::InlinedVector. // // Note: The InlinedVectors in this file (and in cord.h) do not need to use // the same value for their inlined size. The fact that they do is historical. // It may be desirable for each to use a different inlined size optimized for // that InlinedVector's usage. // // TODO(jgm): Benchmark to see if there's a more optimal value than 47 for // the inlined vector size (47 exists for backward compatibility). static const int kInlinedVectorSize = 47; static inline bool IsRootBalanced(CordRep* node) { if (node->tag != CONCAT) { return true; } else if (node->concat()->depth() <= 15) { return true; } else if (node->concat()->depth() > kMinLengthSize) { return false; } else { // Allow depth to become twice as large as implied by fibonacci rule to // reduce rebalancing for larger strings. return (node->length >= min_length[node->concat()->depth() / 2]); } } static CordRep* Rebalance(CordRep* node); static void DumpNode(CordRep* rep, bool include_data, std::ostream* os); static bool VerifyNode(CordRep* root, CordRep* start_node, bool full_validation); static inline CordRep* VerifyTree(CordRep* node) { // Verification is expensive, so only do it in debug mode. // Even in debug mode we normally do only light validation. // If you are debugging Cord itself, you should define the // macro EXTRA_CORD_VALIDATION, e.g. by adding // --copt=-DEXTRA_CORD_VALIDATION to the blaze line. #ifdef EXTRA_CORD_VALIDATION assert(node == nullptr || VerifyNode(node, node, /*full_validation=*/true)); #else // EXTRA_CORD_VALIDATION assert(node == nullptr || VerifyNode(node, node, /*full_validation=*/false)); #endif // EXTRA_CORD_VALIDATION static_cast<void>(&VerifyNode); return node; } // -------------------------------------------------------------------- // Memory management inline CordRep* Ref(CordRep* rep) { if (rep != nullptr) { rep->refcount.Increment(); } return rep; } // This internal routine is called from the cold path of Unref below. Keeping it // in a separate routine allows good inlining of Unref into many profitable call // sites. However, the call to this function can be highly disruptive to the // register pressure in those callers. To minimize the cost to callers, we use // a special LLVM calling convention that preserves most registers. This allows // the call to this routine in cold paths to not disrupt the caller's register // pressure. This calling convention is not available on all platforms; we // intentionally allow LLVM to ignore the attribute rather than attempting to // hardcode the list of supported platforms. #if defined(__clang__) && !defined(__i386__) #pragma clang diagnostic push #pragma clang diagnostic ignored "-Wattributes" __attribute__((preserve_most)) #pragma clang diagnostic pop #endif static void UnrefInternal(CordRep* rep) { assert(rep != nullptr); absl::InlinedVector<CordRep*, kInlinedVectorSize> pending; while (true) { assert(!rep->refcount.IsImmortal()); if (rep->tag == CONCAT) { CordRepConcat* rep_concat = rep->concat(); CordRep* right = rep_concat->right; if (!right->refcount.Decrement()) { pending.push_back(right); } CordRep* left = rep_concat->left; delete rep_concat; rep = nullptr; if (!left->refcount.Decrement()) { rep = left; continue; } } else if (rep->tag == EXTERNAL) { CordRepExternal* rep_external = rep->external(); assert(rep_external->releaser_invoker != nullptr); rep_external->releaser_invoker(rep_external); rep = nullptr; } else if (rep->tag == SUBSTRING) { CordRepSubstring* rep_substring = rep->substring(); CordRep* child = rep_substring->child; delete rep_substring; rep = nullptr; if (!child->refcount.Decrement()) { rep = child; continue; } } else { // Flat CordReps are allocated and constructed with raw ::operator new // and placement new, and must be destructed and deallocated // accordingly. #if defined(__cpp_sized_deallocation) size_t size = TagToAllocatedSize(rep->tag); rep->~CordRep(); ::operator delete(rep, size); #else rep->~CordRep(); ::operator delete(rep); #endif rep = nullptr; } if (!pending.empty()) { rep = pending.back(); pending.pop_back(); } else { break; } } } inline void Unref(CordRep* rep) { // Fast-path for two common, hot cases: a null rep and a shared root. if (ABSL_PREDICT_TRUE(rep == nullptr || rep->refcount.DecrementExpectHighRefcount())) { return; } UnrefInternal(rep); } // Return the depth of a node static int Depth(const CordRep* rep) { if (rep->tag == CONCAT) { return rep->concat()->depth(); } else { return 0; } } static void SetConcatChildren(CordRepConcat* concat, CordRep* left, CordRep* right) { concat->left = left; concat->right = right; concat->length = left->length + right->length; concat->set_depth(1 + std::max(Depth(left), Depth(right))); } // Create a concatenation of the specified nodes. // Does not change the refcounts of "left" and "right". // The returned node has a refcount of 1. static CordRep* RawConcat(CordRep* left, CordRep* right) { // Avoid making degenerate concat nodes (one child is empty) if (left == nullptr || left->length == 0) { Unref(left); return right; } if (right == nullptr || right->length == 0) { Unref(right); return left; } CordRepConcat* rep = new CordRepConcat(); rep->tag = CONCAT; SetConcatChildren(rep, left, right); return rep; } static CordRep* Concat(CordRep* left, CordRep* right) { CordRep* rep = RawConcat(left, right); if (rep != nullptr && !IsRootBalanced(rep)) { rep = Rebalance(rep); } return VerifyTree(rep); } // Make a balanced tree out of an array of leaf nodes. static CordRep* MakeBalancedTree(CordRep** reps, size_t n) { // Make repeated passes over the array, merging adjacent pairs // until we are left with just a single node. while (n > 1) { size_t dst = 0; for (size_t src = 0; src < n; src += 2) { if (src + 1 < n) { reps[dst] = Concat(reps[src], reps[src + 1]); } else { reps[dst] = reps[src]; } dst++; } n = dst; } return reps[0]; } // Create a new flat node. static CordRep* NewFlat(size_t length_hint) { if (length_hint <= kMinFlatLength) { length_hint = kMinFlatLength; } else if (length_hint > kMaxFlatLength) { length_hint = kMaxFlatLength; } // Round size up so it matches a size we can exactly express in a tag. const size_t size = RoundUpForTag(length_hint + kFlatOverhead); void* const raw_rep = ::operator new(size); CordRep* rep = new (raw_rep) CordRep(); rep->tag = AllocatedSizeToTag(size); return VerifyTree(rep); } // Create a new tree out of the specified array. // The returned node has a refcount of 1. static CordRep* NewTree(const char* data, size_t length, size_t alloc_hint) { if (length == 0) return nullptr; absl::FixedArray<CordRep*> reps((length - 1) / kMaxFlatLength + 1); size_t n = 0; do { const size_t len = std::min(length, kMaxFlatLength); CordRep* rep = NewFlat(len + alloc_hint); rep->length = len; memcpy(rep->data, data, len); reps[n++] = VerifyTree(rep); data += len; length -= len; } while (length != 0); return MakeBalancedTree(reps.data(), n); } namespace cord_internal { void InitializeCordRepExternal(absl::string_view data, CordRepExternal* rep) { assert(!data.empty()); rep->length = data.size(); rep->tag = EXTERNAL; rep->base = data.data(); VerifyTree(rep); } } // namespace cord_internal static CordRep* NewSubstring(CordRep* child, size_t offset, size_t length) { // Never create empty substring nodes if (length == 0) { Unref(child); return nullptr; } else { CordRepSubstring* rep = new CordRepSubstring(); assert((offset + length) <= child->length); rep->length = length; rep->tag = SUBSTRING; rep->start = offset; rep->child = child; return VerifyTree(rep); } } // -------------------------------------------------------------------- // Cord::InlineRep functions constexpr unsigned char Cord::InlineRep::kMaxInline; inline void Cord::InlineRep::set_data(const char* data, size_t n, bool nullify_tail) { static_assert(kMaxInline == 15, "set_data is hard-coded for a length of 15"); cord_internal::SmallMemmove(data_.as_chars, data, n, nullify_tail); set_tagged_size(static_cast<char>(n)); } inline char* Cord::InlineRep::set_data(size_t n) { assert(n <= kMaxInline); ResetToEmpty(); set_tagged_size(static_cast<char>(n)); return data_.as_chars; } inline CordRep* Cord::InlineRep::force_tree(size_t extra_hint) { size_t len = tagged_size(); if (len > kMaxInline) { return data_.as_tree.rep; } CordRep* result = NewFlat(len + extra_hint); result->length = len; static_assert(kMinFlatLength >= sizeof(data_.as_chars), ""); memcpy(result->data, data_.as_chars, sizeof(data_.as_chars)); set_tree(result); return result; } inline void Cord::InlineRep::reduce_size(size_t n) { size_t tag = tagged_size(); assert(tag <= kMaxInline); assert(tag >= n); tag -= n; memset(data_.as_chars + tag, 0, n); set_tagged_size(static_cast<char>(tag)); } inline void Cord::InlineRep::remove_prefix(size_t n) { cord_internal::SmallMemmove(data_.as_chars, data_.as_chars + n, tagged_size() - n); reduce_size(n); } void Cord::InlineRep::AppendTree(CordRep* tree) { if (tree == nullptr) return; size_t len = tagged_size(); if (len == 0) { set_tree(tree); } else { set_tree(Concat(force_tree(0), tree)); } } void Cord::InlineRep::PrependTree(CordRep* tree) { assert(tree != nullptr); size_t len = tagged_size(); if (len == 0) { set_tree(tree); } else { set_tree(Concat(tree, force_tree(0))); } } // Searches for a non-full flat node at the rightmost leaf of the tree. If a // suitable leaf is found, the function will update the length field for all // nodes to account for the size increase. The append region address will be // written to region and the actual size increase will be written to size. static inline bool PrepareAppendRegion(CordRep* root, char** region, size_t* size, size_t max_length) { // Search down the right-hand path for a non-full FLAT node. CordRep* dst = root; while (dst->tag == CONCAT && dst->refcount.IsOne()) { dst = dst->concat()->right; } if (dst->tag < FLAT || !dst->refcount.IsOne()) { *region = nullptr; *size = 0; return false; } const size_t in_use = dst->length; const size_t capacity = TagToLength(dst->tag); if (in_use == capacity) { *region = nullptr; *size = 0; return false; } size_t size_increase = std::min(capacity - in_use, max_length); // We need to update the length fields for all nodes, including the leaf node. for (CordRep* rep = root; rep != dst; rep = rep->concat()->right) { rep->length += size_increase; } dst->length += size_increase; *region = dst->data + in_use; *size = size_increase; return true; } void Cord::InlineRep::GetAppendRegion(char** region, size_t* size, size_t max_length) { if (max_length == 0) { *region = nullptr; *size = 0; return; } // Try to fit in the inline buffer if possible. size_t inline_length = tagged_size(); if (inline_length < kMaxInline && max_length <= kMaxInline - inline_length) { *region = data_.as_chars + inline_length; *size = max_length; set_tagged_size(static_cast<char>(inline_length + max_length)); return; } CordRep* root = force_tree(max_length); if (PrepareAppendRegion(root, region, size, max_length)) { return; } // Allocate new node. CordRep* new_node = NewFlat(std::max(static_cast<size_t>(root->length), max_length)); new_node->length = std::min(static_cast<size_t>(TagToLength(new_node->tag)), max_length); *region = new_node->data; *size = new_node->length; replace_tree(Concat(root, new_node)); } void Cord::InlineRep::GetAppendRegion(char** region, size_t* size) { const size_t max_length = std::numeric_limits<size_t>::max(); // Try to fit in the inline buffer if possible. size_t inline_length = tagged_size(); if (inline_length < kMaxInline) { *region = data_.as_chars + inline_length; *size = kMaxInline - inline_length; set_tagged_size(kMaxInline); return; } CordRep* root = force_tree(max_length); if (PrepareAppendRegion(root, region, size, max_length)) { return; } // Allocate new node. CordRep* new_node = NewFlat(root->length); new_node->length = TagToLength(new_node->tag); *region = new_node->data; *size = new_node->length; replace_tree(Concat(root, new_node)); } // If the rep is a leaf, this will increment the value at total_mem_usage and // will return true. static bool RepMemoryUsageLeaf(const CordRep* rep, size_t* total_mem_usage) { if (rep->tag >= FLAT) { *total_mem_usage += TagToAllocatedSize(rep->tag); return true; } if (rep->tag == EXTERNAL) { *total_mem_usage += sizeof(CordRepConcat) + rep->length; return true; } return false; } void Cord::InlineRep::AssignSlow(const Cord::InlineRep& src) { ClearSlow(); data_ = src.data_; if (is_tree()) { Ref(tree()); } } void Cord::InlineRep::ClearSlow() { if (is_tree()) { Unref(tree()); } ResetToEmpty(); } // -------------------------------------------------------------------- // Constructors and destructors Cord::Cord(const Cord& src) : contents_(src.contents_) { Ref(contents_.tree()); // Does nothing if contents_ has embedded data } Cord::Cord(absl::string_view src) { const size_t n = src.size(); if (n <= InlineRep::kMaxInline) { contents_.set_data(src.data(), n, false); } else { contents_.set_tree(NewTree(src.data(), n, 0)); } } template <typename T, Cord::EnableIfString<T>> Cord::Cord(T&& src) { if ( // String is short: copy data to avoid external block overhead. src.size() <= kMaxBytesToCopy || // String is wasteful: copy data to avoid pinning too much unused memory. src.size() < src.capacity() / 2 ) { if (src.size() <= InlineRep::kMaxInline) { contents_.set_data(src.data(), src.size(), false); } else { contents_.set_tree(NewTree(src.data(), src.size(), 0)); } } else { struct StringReleaser { void operator()(absl::string_view /* data */) {} std::string data; }; const absl::string_view original_data = src; auto* rep = static_cast< ::absl::cord_internal::CordRepExternalImpl<StringReleaser>*>( absl::cord_internal::NewExternalRep( original_data, StringReleaser{std::forward<T>(src)})); // Moving src may have invalidated its data pointer, so adjust it. rep->base = rep->template get<0>().data.data(); contents_.set_tree(rep); } } template Cord::Cord(std::string&& src); // The destruction code is separate so that the compiler can determine // that it does not need to call the destructor on a moved-from Cord. void Cord::DestroyCordSlow() { Unref(VerifyTree(contents_.tree())); } // -------------------------------------------------------------------- // Mutators void Cord::Clear() { Unref(contents_.clear()); } Cord& Cord::operator=(absl::string_view src) { const char* data = src.data(); size_t length = src.size(); CordRep* tree = contents_.tree(); if (length <= InlineRep::kMaxInline) { // Embed into this->contents_ contents_.set_data(data, length, true); Unref(tree); return *this; } if (tree != nullptr && tree->tag >= FLAT && TagToLength(tree->tag) >= length && tree->refcount.IsOne()) { // Copy in place if the existing FLAT node is reusable. memmove(tree->data, data, length); tree->length = length; VerifyTree(tree); return *this; } contents_.set_tree(NewTree(data, length, 0)); Unref(tree); return *this; } template <typename T, Cord::EnableIfString<T>> Cord& Cord::operator=(T&& src) { if (src.size() <= kMaxBytesToCopy) { *this = absl::string_view(src); } else { *this = Cord(std::forward<T>(src)); } return *this; } template Cord& Cord::operator=(std::string&& src); // TODO(sanjay): Move to Cord::InlineRep section of file. For now, // we keep it here to make diffs easier. void Cord::InlineRep::AppendArray(const char* src_data, size_t src_size) { if (src_size == 0) return; // memcpy(_, nullptr, 0) is undefined. // Try to fit in the inline buffer if possible. size_t inline_length = tagged_size(); if (inline_length < kMaxInline && src_size <= kMaxInline - inline_length) { // Append new data to embedded array set_tagged_size(static_cast<char>(inline_length + src_size)); memcpy(data_.as_chars + inline_length, src_data, src_size); return; } CordRep* root = tree(); size_t appended = 0; if (root) { char* region; if (PrepareAppendRegion(root, ®ion, &appended, src_size)) { memcpy(region, src_data, appended); } } else { // It is possible that src_data == data_, but when we transition from an // InlineRep to a tree we need to assign data_ = root via set_tree. To // avoid corrupting the source data before we copy it, delay calling // set_tree until after we've copied data. // We are going from an inline size to beyond inline size. Make the new size // either double the inlined size, or the added size + 10%. const size_t size1 = inline_length * 2 + src_size; const size_t size2 = inline_length + src_size / 10; root = NewFlat(std::max<size_t>(size1, size2)); appended = std::min(src_size, TagToLength(root->tag) - inline_length); memcpy(root->data, data_.as_chars, inline_length); memcpy(root->data + inline_length, src_data, appended); root->length = inline_length + appended; set_tree(root); } src_data += appended; src_size -= appended; if (src_size == 0) { return; } // Use new block(s) for any remaining bytes that were not handled above. // Alloc extra memory only if the right child of the root of the new tree is // going to be a FLAT node, which will permit further inplace appends. size_t length = src_size; if (src_size < kMaxFlatLength) { // The new length is either // - old size + 10% // - old_size + src_size // This will cause a reasonable conservative step-up in size that is still // large enough to avoid excessive amounts of small fragments being added. length = std::max<size_t>(root->length / 10, src_size); } set_tree(Concat(root, NewTree(src_data, src_size, length - src_size))); } inline CordRep* Cord::TakeRep() const& { return Ref(contents_.tree()); } inline CordRep* Cord::TakeRep() && { CordRep* rep = contents_.tree(); contents_.clear(); return rep; } template <typename C> inline void Cord::AppendImpl(C&& src) { if (empty()) { // In case of an empty destination avoid allocating a new node, do not copy // data. *this = std::forward<C>(src); return; } // For short cords, it is faster to copy data if there is room in dst. const size_t src_size = src.contents_.size(); if (src_size <= kMaxBytesToCopy) { CordRep* src_tree = src.contents_.tree(); if (src_tree == nullptr) { // src has embedded data. contents_.AppendArray(src.contents_.data(), src_size); return; } if (src_tree->tag >= FLAT) { // src tree just has one flat node. contents_.AppendArray(src_tree->data, src_size); return; } if (&src == this) { // ChunkIterator below assumes that src is not modified during traversal. Append(Cord(src)); return; } // TODO(mec): Should we only do this if "dst" has space? for (absl::string_view chunk : src.Chunks()) { Append(chunk); } return; } contents_.AppendTree(std::forward<C>(src).TakeRep()); } void Cord::Append(const Cord& src) { AppendImpl(src); } void Cord::Append(Cord&& src) { AppendImpl(std::move(src)); } template <typename T, Cord::EnableIfString<T>> void Cord::Append(T&& src) { if (src.size() <= kMaxBytesToCopy) { Append(absl::string_view(src)); } else { Append(Cord(std::forward<T>(src))); } } template void Cord::Append(std::string&& src); void Cord::Prepend(const Cord& src) { CordRep* src_tree = src.contents_.tree(); if (src_tree != nullptr) { Ref(src_tree); contents_.PrependTree(src_tree); return; } // `src` cord is inlined. absl::string_view src_contents(src.contents_.data(), src.contents_.size()); return Prepend(src_contents); } void Cord::Prepend(absl::string_view src) { if (src.empty()) return; // memcpy(_, nullptr, 0) is undefined. size_t cur_size = contents_.size(); if (!contents_.is_tree() && cur_size + src.size() <= InlineRep::kMaxInline) { // Use embedded storage. char data[InlineRep::kMaxInline + 1] = {0}; data[InlineRep::kMaxInline] = cur_size + src.size(); // set size memcpy(data, src.data(), src.size()); memcpy(data + src.size(), contents_.data(), cur_size); memcpy(reinterpret_cast<void*>(&contents_), data, InlineRep::kMaxInline + 1); } else { contents_.PrependTree(NewTree(src.data(), src.size(), 0)); } } template <typename T, Cord::EnableIfString<T>> inline void Cord::Prepend(T&& src) { if (src.size() <= kMaxBytesToCopy) { Prepend(absl::string_view(src)); } else { Prepend(Cord(std::forward<T>(src))); } } template void Cord::Prepend(std::string&& src); static CordRep* RemovePrefixFrom(CordRep* node, size_t n) { if (n >= node->length) return nullptr; if (n == 0) return Ref(node); absl::InlinedVector<CordRep*, kInlinedVectorSize> rhs_stack; while (node->tag == CONCAT) { assert(n <= node->length); if (n < node->concat()->left->length) { // Push right to stack, descend left. rhs_stack.push_back(node->concat()->right); node = node->concat()->left; } else { // Drop left, descend right. n -= node->concat()->left->length; node = node->concat()->right; } } assert(n <= node->length); if (n == 0) { Ref(node); } else { size_t start = n; size_t len = node->length - n; if (node->tag == SUBSTRING) { // Consider in-place update of node, similar to in RemoveSuffixFrom(). start += node->substring()->start; node = node->substring()->child; } node = NewSubstring(Ref(node), start, len); } while (!rhs_stack.empty()) { node = Concat(node, Ref(rhs_stack.back())); rhs_stack.pop_back(); } return node; } // RemoveSuffixFrom() is very similar to RemovePrefixFrom(), with the // exception that removing a suffix has an optimization where a node may be // edited in place iff that node and all its ancestors have a refcount of 1. static CordRep* RemoveSuffixFrom(CordRep* node, size_t n) { if (n >= node->length) return nullptr; if (n == 0) return Ref(node); absl::InlinedVector<CordRep*, kInlinedVectorSize> lhs_stack; bool inplace_ok = node->refcount.IsOne(); while (node->tag == CONCAT) { assert(n <= node->length); if (n < node->concat()->right->length) { // Push left to stack, descend right. lhs_stack.push_back(node->concat()->left); node = node->concat()->right; } else { // Drop right, descend left. n -= node->concat()->right->length; node = node->concat()->left; } inplace_ok = inplace_ok && node->refcount.IsOne(); } assert(n <= node->length); if (n == 0) { Ref(node); } else if (inplace_ok && node->tag != EXTERNAL) { // Consider making a new buffer if the current node capacity is much // larger than the new length. Ref(node); node->length -= n; } else { size_t start = 0; size_t len = node->length - n; if (node->tag == SUBSTRING) { start = node->substring()->start; node = node->substring()->child; } node = NewSubstring(Ref(node), start, len); } while (!lhs_stack.empty()) { node = Concat(Ref(lhs_stack.back()), node); lhs_stack.pop_back(); } return node; } void Cord::RemovePrefix(size_t n) { ABSL_INTERNAL_CHECK(n <= size(), absl::StrCat("Requested prefix size ", n, " exceeds Cord's size ", size())); CordRep* tree = contents_.tree(); if (tree == nullptr) { contents_.remove_prefix(n); } else { CordRep* newrep = RemovePrefixFrom(tree, n); Unref(tree); contents_.replace_tree(VerifyTree(newrep)); } } void Cord::RemoveSuffix(size_t n) { ABSL_INTERNAL_CHECK(n <= size(), absl::StrCat("Requested suffix size ", n, " exceeds Cord's size ", size())); CordRep* tree = contents_.tree(); if (tree == nullptr) { contents_.reduce_size(n); } else { CordRep* newrep = RemoveSuffixFrom(tree, n); Unref(tree); contents_.replace_tree(VerifyTree(newrep)); } } // Work item for NewSubRange(). struct SubRange { SubRange(CordRep* a_node, size_t a_pos, size_t a_n) : node(a_node), pos(a_pos), n(a_n) {} CordRep* node; // nullptr means concat last 2 results. size_t pos; size_t n; }; static CordRep* NewSubRange(CordRep* node, size_t pos, size_t n) { absl::InlinedVector<CordRep*, kInlinedVectorSize> results; absl::InlinedVector<SubRange, kInlinedVectorSize> todo; todo.push_back(SubRange(node, pos, n)); do { const SubRange& sr = todo.back(); node = sr.node; pos = sr.pos; n = sr.n; todo.pop_back(); if (node == nullptr) { assert(results.size() >= 2); CordRep* right = results.back(); results.pop_back(); CordRep* left = results.back(); results.pop_back(); results.push_back(Concat(left, right)); } else if (pos == 0 && n == node->length) { results.push_back(Ref(node)); } else if (node->tag != CONCAT) { if (node->tag == SUBSTRING) { pos += node->substring()->start; node = node->substring()->child; } results.push_back(NewSubstring(Ref(node), pos, n)); } else if (pos + n <= node->concat()->left->length) { todo.push_back(SubRange(node->concat()->left, pos, n)); } else if (pos >= node->concat()->left->length) { pos -= node->concat()->left->length; todo.push_back(SubRange(node->concat()->right, pos, n)); } else { size_t left_n = node->concat()->left->length - pos; todo.push_back(SubRange(nullptr, 0, 0)); // Concat() todo.push_back(SubRange(node->concat()->right, 0, n - left_n)); todo.push_back(SubRange(node->concat()->left, pos, left_n)); } } while (!todo.empty()); assert(results.size() == 1); return results[0]; } Cord Cord::Subcord(size_t pos, size_t new_size) const { Cord sub_cord; size_t length = size(); if (pos > length) pos = length; if (new_size > length - pos) new_size = length - pos; CordRep* tree = contents_.tree(); if (tree == nullptr) { // sub_cord is newly constructed, no need to re-zero-out the tail of // contents_ memory. sub_cord.contents_.set_data(contents_.data() + pos, new_size, false); } else if (new_size == 0) { // We want to return empty subcord, so nothing to do. } else if (new_size <= InlineRep::kMaxInline) { Cord::ChunkIterator it = chunk_begin(); it.AdvanceBytes(pos); char* dest = sub_cord.contents_.data_.as_chars; size_t remaining_size = new_size; while (remaining_size > it->size()) { cord_internal::SmallMemmove(dest, it->data(), it->size()); remaining_size -= it->size(); dest += it->size(); ++it; } cord_internal::SmallMemmove(dest, it->data(), remaining_size); sub_cord.contents_.set_tagged_size(new_size); } else { sub_cord.contents_.set_tree(NewSubRange(tree, pos, new_size)); } return sub_cord; } // -------------------------------------------------------------------- // Balancing class CordForest { public: explicit CordForest(size_t length) : root_length_(length), trees_(kMinLengthSize, nullptr) {} void Build(CordRep* cord_root) { std::vector<CordRep*> pending = {cord_root}; while (!pending.empty()) { CordRep* node = pending.back(); pending.pop_back(); CheckNode(node); if (ABSL_PREDICT_FALSE(node->tag != CONCAT)) { AddNode(node); continue; } CordRepConcat* concat_node = node->concat(); if (concat_node->depth() >= kMinLengthSize || concat_node->length < min_length[concat_node->depth()]) { pending.push_back(concat_node->right); pending.push_back(concat_node->left); if (concat_node->refcount.IsOne()) { concat_node->left = concat_freelist_; concat_freelist_ = concat_node; } else { Ref(concat_node->right); Ref(concat_node->left); Unref(concat_node); } } else { AddNode(node); } } } CordRep* ConcatNodes() { CordRep* sum = nullptr; for (auto* node : trees_) { if (node == nullptr) continue; sum = PrependNode(node, sum); root_length_ -= node->length; if (root_length_ == 0) break; } ABSL_INTERNAL_CHECK(sum != nullptr, "Failed to locate sum node"); return VerifyTree(sum); } private: CordRep* AppendNode(CordRep* node, CordRep* sum) { return (sum == nullptr) ? node : MakeConcat(sum, node); } CordRep* PrependNode(CordRep* node, CordRep* sum) { return (sum == nullptr) ? node : MakeConcat(node, sum); } void AddNode(CordRep* node) { CordRep* sum = nullptr; // Collect together everything with which we will merge with node int i = 0; for (; node->length > min_length[i + 1]; ++i) { auto& tree_at_i = trees_[i]; if (tree_at_i == nullptr) continue; sum = PrependNode(tree_at_i, sum); tree_at_i = nullptr; } sum = AppendNode(node, sum); // Insert sum into appropriate place in the forest for (; sum->length >= min_length[i]; ++i) { auto& tree_at_i = trees_[i]; if (tree_at_i == nullptr) continue; sum = MakeConcat(tree_at_i, sum); tree_at_i = nullptr; } // min_length[0] == 1, which means sum->length >= min_length[0] assert(i > 0); trees_[i - 1] = sum; } // Make concat node trying to resue existing CordRepConcat nodes we // already collected in the concat_freelist_. CordRep* MakeConcat(CordRep* left, CordRep* right) { if (concat_freelist_ == nullptr) return RawConcat(left, right); CordRepConcat* rep = concat_freelist_; if (concat_freelist_->left == nullptr) { concat_freelist_ = nullptr; } else { concat_freelist_ = concat_freelist_->left->concat(); } SetConcatChildren(rep, left, right); return rep; } static void CheckNode(CordRep* node) { ABSL_INTERNAL_CHECK(node->length != 0u, ""); if (node->tag == CONCAT) { ABSL_INTERNAL_CHECK(node->concat()->left != nullptr, ""); ABSL_INTERNAL_CHECK(node->concat()->right != nullptr, ""); ABSL_INTERNAL_CHECK(node->length == (node->concat()->left->length + node->concat()->right->length), ""); } } size_t root_length_; // use an inlined vector instead of a flat array to get bounds checking absl::InlinedVector<CordRep*, kInlinedVectorSize> trees_; // List of concat nodes we can re-use for Cord balancing. CordRepConcat* concat_freelist_ = nullptr; }; static CordRep* Rebalance(CordRep* node) { VerifyTree(node); assert(node->tag == CONCAT); if (node->length == 0) { return nullptr; } CordForest forest(node->length); forest.Build(node); return forest.ConcatNodes(); } // -------------------------------------------------------------------- // Comparators namespace { int ClampResult(int memcmp_res) { return static_cast<int>(memcmp_res > 0) - static_cast<int>(memcmp_res < 0); } int CompareChunks(absl::string_view* lhs, absl::string_view* rhs, size_t* size_to_compare) { size_t compared_size = std::min(lhs->size(), rhs->size()); assert(*size_to_compare >= compared_size); *size_to_compare -= compared_size; int memcmp_res = ::memcmp(lhs->data(), rhs->data(), compared_size); if (memcmp_res != 0) return memcmp_res; lhs->remove_prefix(compared_size); rhs->remove_prefix(compared_size); return 0; } // This overload set computes comparison results from memcmp result. This // interface is used inside GenericCompare below. Differet implementations // are specialized for int and bool. For int we clamp result to {-1, 0, 1} // set. For bool we just interested in "value == 0". template <typename ResultType> ResultType ComputeCompareResult(int memcmp_res) { return ClampResult(memcmp_res); } template <> bool ComputeCompareResult<bool>(int memcmp_res) { return memcmp_res == 0; } } // namespace // Helper routine. Locates the first flat chunk of the Cord without // initializing the iterator. inline absl::string_view Cord::InlineRep::FindFlatStartPiece() const { size_t n = tagged_size(); if (n <= kMaxInline) { return absl::string_view(data_.as_chars, n); } CordRep* node = tree(); if (node->tag >= FLAT) { return absl::string_view(node->data, node->length); } if (node->tag == EXTERNAL) { return absl::string_view(node->external()->base, node->length); } // Walk down the left branches until we hit a non-CONCAT node. while (node->tag == CONCAT) { node = node->concat()->left; } // Get the child node if we encounter a SUBSTRING. size_t offset = 0; size_t length = node->length; assert(length != 0); if (node->tag == SUBSTRING) { offset = node->substring()->start; node = node->substring()->child; } if (node->tag >= FLAT) { return absl::string_view(node->data + offset, length); } assert((node->tag == EXTERNAL) && "Expect FLAT or EXTERNAL node here"); return absl::string_view(node->external()->base + offset, length); } inline int Cord::CompareSlowPath(absl::string_view rhs, size_t compared_size, size_t size_to_compare) const { auto advance = [](Cord::ChunkIterator* it, absl::string_view* chunk) { if (!chunk->empty()) return true; ++*it; if (it->bytes_remaining_ == 0) return false; *chunk = **it; return true; }; Cord::ChunkIterator lhs_it = chunk_begin(); // compared_size is inside first chunk. absl::string_view lhs_chunk = (lhs_it.bytes_remaining_ != 0) ? *lhs_it : absl::string_view(); assert(compared_size <= lhs_chunk.size()); assert(compared_size <= rhs.size()); lhs_chunk.remove_prefix(compared_size); rhs.remove_prefix(compared_size); size_to_compare -= compared_size; // skip already compared size. while (advance(&lhs_it, &lhs_chunk) && !rhs.empty()) { int comparison_result = CompareChunks(&lhs_chunk, &rhs, &size_to_compare); if (comparison_result != 0) return comparison_result; if (size_to_compare == 0) return 0; } return static_cast<int>(rhs.empty()) - static_cast<int>(lhs_chunk.empty()); } inline int Cord::CompareSlowPath(const Cord& rhs, size_t compared_size, size_t size_to_compare) const { auto advance = [](Cord::ChunkIterator* it, absl::string_view* chunk) { if (!chunk->empty()) return true; ++*it; if (it->bytes_remaining_ == 0) return false; *chunk = **it; return true; }; Cord::ChunkIterator lhs_it = chunk_begin(); Cord::ChunkIterator rhs_it = rhs.chunk_begin(); // compared_size is inside both first chunks. absl::string_view lhs_chunk = (lhs_it.bytes_remaining_ != 0) ? *lhs_it : absl::string_view(); absl::string_view rhs_chunk = (rhs_it.bytes_remaining_ != 0) ? *rhs_it : absl::string_view(); assert(compared_size <= lhs_chunk.size()); assert(compared_size <= rhs_chunk.size()); lhs_chunk.remove_prefix(compared_size); rhs_chunk.remove_prefix(compared_size); size_to_compare -= compared_size; // skip already compared size. while (advance(&lhs_it, &lhs_chunk) && advance(&rhs_it, &rhs_chunk)) { int memcmp_res = CompareChunks(&lhs_chunk, &rhs_chunk, &size_to_compare); if (memcmp_res != 0) return memcmp_res; if (size_to_compare == 0) return 0; } return static_cast<int>(rhs_chunk.empty()) - static_cast<int>(lhs_chunk.empty()); } inline absl::string_view Cord::GetFirstChunk(const Cord& c) { return c.contents_.FindFlatStartPiece(); } inline absl::string_view Cord::GetFirstChunk(absl::string_view sv) { return sv; } // Compares up to 'size_to_compare' bytes of 'lhs' with 'rhs'. It is assumed // that 'size_to_compare' is greater that size of smallest of first chunks. template <typename ResultType, typename RHS> ResultType GenericCompare(const Cord& lhs, const RHS& rhs, size_t size_to_compare) { absl::string_view lhs_chunk = Cord::GetFirstChunk(lhs); absl::string_view rhs_chunk = Cord::GetFirstChunk(rhs); size_t compared_size = std::min(lhs_chunk.size(), rhs_chunk.size()); assert(size_to_compare >= compared_size); int memcmp_res = ::memcmp(lhs_chunk.data(), rhs_chunk.data(), compared_size); if (compared_size == size_to_compare || memcmp_res != 0) { return ComputeCompareResult<ResultType>(memcmp_res); } return ComputeCompareResult<ResultType>( lhs.CompareSlowPath(rhs, compared_size, size_to_compare)); } bool Cord::EqualsImpl(absl::string_view rhs, size_t size_to_compare) const { return GenericCompare<bool>(*this, rhs, size_to_compare); } bool Cord::EqualsImpl(const Cord& rhs, size_t size_to_compare) const { return GenericCompare<bool>(*this, rhs, size_to_compare); } template <typename RHS> inline int SharedCompareImpl(const Cord& lhs, const RHS& rhs) { size_t lhs_size = lhs.size(); size_t rhs_size = rhs.size(); if (lhs_size == rhs_size) { return GenericCompare<int>(lhs, rhs, lhs_size); } if (lhs_size < rhs_size) { auto data_comp_res = GenericCompare<int>(lhs, rhs, lhs_size); return data_comp_res == 0 ? -1 : data_comp_res; } auto data_comp_res = GenericCompare<int>(lhs, rhs, rhs_size); return data_comp_res == 0 ? +1 : data_comp_res; } int Cord::Compare(absl::string_view rhs) const { return SharedCompareImpl(*this, rhs); } int Cord::CompareImpl(const Cord& rhs) const { return SharedCompareImpl(*this, rhs); } bool Cord::EndsWith(absl::string_view rhs) const { size_t my_size = size(); size_t rhs_size = rhs.size(); if (my_size < rhs_size) return false; Cord tmp(*this); tmp.RemovePrefix(my_size - rhs_size); return tmp.EqualsImpl(rhs, rhs_size); } bool Cord::EndsWith(const Cord& rhs) const { size_t my_size = size(); size_t rhs_size = rhs.size(); if (my_size < rhs_size) return false; Cord tmp(*this); tmp.RemovePrefix(my_size - rhs_size); return tmp.EqualsImpl(rhs, rhs_size); } // -------------------------------------------------------------------- // Misc. Cord::operator std::string() const { std::string s; absl::CopyCordToString(*this, &s); return s; } void CopyCordToString(const Cord& src, std::string* dst) { if (!src.contents_.is_tree()) { src.contents_.CopyTo(dst); } else { absl::strings_internal::STLStringResizeUninitialized(dst, src.size()); src.CopyToArraySlowPath(&(*dst)[0]); } } void Cord::CopyToArraySlowPath(char* dst) const { assert(contents_.is_tree()); absl::string_view fragment; if (GetFlatAux(contents_.tree(), &fragment)) { memcpy(dst, fragment.data(), fragment.size()); return; } for (absl::string_view chunk : Chunks()) { memcpy(dst, chunk.data(), chunk.size()); dst += chunk.size(); } } Cord::ChunkIterator& Cord::ChunkIterator::operator++() { ABSL_HARDENING_ASSERT(bytes_remaining_ > 0 && "Attempted to iterate past `end()`"); assert(bytes_remaining_ >= current_chunk_.size()); bytes_remaining_ -= current_chunk_.size(); if (stack_of_right_children_.empty()) { assert(!current_chunk_.empty()); // Called on invalid iterator. // We have reached the end of the Cord. return *this; } // Process the next node on the stack. CordRep* node = stack_of_right_children_.back(); stack_of_right_children_.pop_back(); // Walk down the left branches until we hit a non-CONCAT node. Save the // right children to the stack for subsequent traversal. while (node->tag == CONCAT) { stack_of_right_children_.push_back(node->concat()->right); node = node->concat()->left; } // Get the child node if we encounter a SUBSTRING. size_t offset = 0; size_t length = node->length; if (node->tag == SUBSTRING) { offset = node->substring()->start; node = node->substring()->child; } assert(node->tag == EXTERNAL || node->tag >= FLAT); assert(length != 0); const char* data = node->tag == EXTERNAL ? node->external()->base : node->data; current_chunk_ = absl::string_view(data + offset, length); current_leaf_ = node; return *this; } Cord Cord::ChunkIterator::AdvanceAndReadBytes(size_t n) { ABSL_HARDENING_ASSERT(bytes_remaining_ >= n && "Attempted to iterate past `end()`"); Cord subcord; if (n <= InlineRep::kMaxInline) { // Range to read fits in inline data. Flatten it. char* data = subcord.contents_.set_data(n); while (n > current_chunk_.size()) { memcpy(data, current_chunk_.data(), current_chunk_.size()); data += current_chunk_.size(); n -= current_chunk_.size(); ++*this; } memcpy(data, current_chunk_.data(), n); if (n < current_chunk_.size()) { RemoveChunkPrefix(n); } else if (n > 0) { ++*this; } return subcord; } if (n < current_chunk_.size()) { // Range to read is a proper subrange of the current chunk. assert(current_leaf_ != nullptr); CordRep* subnode = Ref(current_leaf_); const char* data = subnode->tag == EXTERNAL ? subnode->external()->base : subnode->data; subnode = NewSubstring(subnode, current_chunk_.data() - data, n); subcord.contents_.set_tree(VerifyTree(subnode)); RemoveChunkPrefix(n); return subcord; } // Range to read begins with a proper subrange of the current chunk. assert(!current_chunk_.empty()); assert(current_leaf_ != nullptr); CordRep* subnode = Ref(current_leaf_); if (current_chunk_.size() < subnode->length) { const char* data = subnode->tag == EXTERNAL ? subnode->external()->base : subnode->data; subnode = NewSubstring(subnode, current_chunk_.data() - data, current_chunk_.size()); } n -= current_chunk_.size(); bytes_remaining_ -= current_chunk_.size(); // Process the next node(s) on the stack, reading whole subtrees depending on // their length and how many bytes we are advancing. CordRep* node = nullptr; while (!stack_of_right_children_.empty()) { node = stack_of_right_children_.back(); stack_of_right_children_.pop_back(); if (node->length > n) break; // TODO(qrczak): This might unnecessarily recreate existing concat nodes. // Avoiding that would need pretty complicated logic (instead of // current_leaf_, keep current_subtree_ which points to the highest node // such that the current leaf can be found on the path of left children // starting from current_subtree_; delay creating subnode while node is // below current_subtree_; find the proper node along the path of left // children starting from current_subtree_ if this loop exits while staying // below current_subtree_; etc.; alternatively, push parents instead of // right children on the stack). subnode = Concat(subnode, Ref(node)); n -= node->length; bytes_remaining_ -= node->length; node = nullptr; } if (node == nullptr) { // We have reached the end of the Cord. assert(bytes_remaining_ == 0); subcord.contents_.set_tree(VerifyTree(subnode)); return subcord; } // Walk down the appropriate branches until we hit a non-CONCAT node. Save the // right children to the stack for subsequent traversal. while (node->tag == CONCAT) { if (node->concat()->left->length > n) { // Push right, descend left. stack_of_right_children_.push_back(node->concat()->right); node = node->concat()->left; } else { // Read left, descend right. subnode = Concat(subnode, Ref(node->concat()->left)); n -= node->concat()->left->length; bytes_remaining_ -= node->concat()->left->length; node = node->concat()->right; } } // Get the child node if we encounter a SUBSTRING. size_t offset = 0; size_t length = node->length; if (node->tag == SUBSTRING) { offset = node->substring()->start; node = node->substring()->child; } // Range to read ends with a proper (possibly empty) subrange of the current // chunk. assert(node->tag == EXTERNAL || node->tag >= FLAT); assert(length > n); if (n > 0) subnode = Concat(subnode, NewSubstring(Ref(node), offset, n)); const char* data = node->tag == EXTERNAL ? node->external()->base : node->data; current_chunk_ = absl::string_view(data + offset + n, length - n); current_leaf_ = node; bytes_remaining_ -= n; subcord.contents_.set_tree(VerifyTree(subnode)); return subcord; } void Cord::ChunkIterator::AdvanceBytesSlowPath(size_t n) { assert(bytes_remaining_ >= n && "Attempted to iterate past `end()`"); assert(n >= current_chunk_.size()); // This should only be called when // iterating to a new node. n -= current_chunk_.size(); bytes_remaining_ -= current_chunk_.size(); // Process the next node(s) on the stack, skipping whole subtrees depending on // their length and how many bytes we are advancing. CordRep* node = nullptr; while (!stack_of_right_children_.empty()) { node = stack_of_right_children_.back(); stack_of_right_children_.pop_back(); if (node->length > n) break; n -= node->length; bytes_remaining_ -= node->length; node = nullptr; } if (node == nullptr) { // We have reached the end of the Cord. assert(bytes_remaining_ == 0); return; } // Walk down the appropriate branches until we hit a non-CONCAT node. Save the // right children to the stack for subsequent traversal. while (node->tag == CONCAT) { if (node->concat()->left->length > n) { // Push right, descend left. stack_of_right_children_.push_back(node->concat()->right); node = node->concat()->left; } else { // Skip left, descend right. n -= node->concat()->left->length; bytes_remaining_ -= node->concat()->left->length; node = node->concat()->right; } } // Get the child node if we encounter a SUBSTRING. size_t offset = 0; size_t length = node->length; if (node->tag == SUBSTRING) { offset = node->substring()->start; node = node->substring()->child; } assert(node->tag == EXTERNAL || node->tag >= FLAT); assert(length > n); const char* data = node->tag == EXTERNAL ? node->external()->base : node->data; current_chunk_ = absl::string_view(data + offset + n, length - n); current_leaf_ = node; bytes_remaining_ -= n; } char Cord::operator[](size_t i) const { ABSL_HARDENING_ASSERT(i < size()); size_t offset = i; const CordRep* rep = contents_.tree(); if (rep == nullptr) { return contents_.data()[i]; } while (true) { assert(rep != nullptr); assert(offset < rep->length); if (rep->tag >= FLAT) { // Get the "i"th character directly from the flat array. return rep->data[offset]; } else if (rep->tag == EXTERNAL) { // Get the "i"th character from the external array. return rep->external()->base[offset]; } else if (rep->tag == CONCAT) { // Recursively branch to the side of the concatenation that the "i"th // character is on. size_t left_length = rep->concat()->left->length; if (offset < left_length) { rep = rep->concat()->left; } else { offset -= left_length; rep = rep->concat()->right; } } else { // This must be a substring a node, so bypass it to get to the child. assert(rep->tag == SUBSTRING); offset += rep->substring()->start; rep = rep->substring()->child; } } } absl::string_view Cord::FlattenSlowPath() { size_t total_size = size(); CordRep* new_rep; char* new_buffer; // Try to put the contents into a new flat rep. If they won't fit in the // biggest possible flat node, use an external rep instead. if (total_size <= kMaxFlatLength) { new_rep = NewFlat(total_size); new_rep->length = total_size; new_buffer = new_rep->data; CopyToArraySlowPath(new_buffer); } else { new_buffer = std::allocator<char>().allocate(total_size); CopyToArraySlowPath(new_buffer); new_rep = absl::cord_internal::NewExternalRep( absl::string_view(new_buffer, total_size), [](absl::string_view s) { std::allocator<char>().deallocate(const_cast<char*>(s.data()), s.size()); }); } Unref(contents_.tree()); contents_.set_tree(new_rep); return absl::string_view(new_buffer, total_size); } /* static */ bool Cord::GetFlatAux(CordRep* rep, absl::string_view* fragment) { assert(rep != nullptr); if (rep->tag >= FLAT) { *fragment = absl::string_view(rep->data, rep->length); return true; } else if (rep->tag == EXTERNAL) { *fragment = absl::string_view(rep->external()->base, rep->length); return true; } else if (rep->tag == SUBSTRING) { CordRep* child = rep->substring()->child; if (child->tag >= FLAT) { *fragment = absl::string_view(child->data + rep->substring()->start, rep->length); return true; } else if (child->tag == EXTERNAL) { *fragment = absl::string_view( child->external()->base + rep->substring()->start, rep->length); return true; } } return false; } /* static */ void Cord::ForEachChunkAux( absl::cord_internal::CordRep* rep, absl::FunctionRef<void(absl::string_view)> callback) { assert(rep != nullptr); int stack_pos = 0; constexpr int stack_max = 128; // Stack of right branches for tree traversal absl::cord_internal::CordRep* stack[stack_max]; absl::cord_internal::CordRep* current_node = rep; while (true) { if (current_node->tag == CONCAT) { if (stack_pos == stack_max) { // There's no more room on our stack array to add another right branch, // and the idea is to avoid allocations, so call this function // recursively to navigate this subtree further. (This is not something // we expect to happen in practice). ForEachChunkAux(current_node, callback); // Pop the next right branch and iterate. current_node = stack[--stack_pos]; continue; } else { // Save the right branch for later traversal and continue down the left // branch. stack[stack_pos++] = current_node->concat()->right; current_node = current_node->concat()->left; continue; } } // This is a leaf node, so invoke our callback. absl::string_view chunk; bool success = GetFlatAux(current_node, &chunk); assert(success); if (success) { callback(chunk); } if (stack_pos == 0) { // end of traversal return; } current_node = stack[--stack_pos]; } } static void DumpNode(CordRep* rep, bool include_data, std::ostream* os) { const int kIndentStep = 1; int indent = 0; absl::InlinedVector<CordRep*, kInlinedVectorSize> stack; absl::InlinedVector<int, kInlinedVectorSize> indents; for (;;) { *os << std::setw(3) << rep->refcount.Get(); *os << " " << std::setw(7) << rep->length; *os << " ["; if (include_data) *os << static_cast<void*>(rep); *os << "]"; *os << " " << (IsRootBalanced(rep) ? 'b' : 'u'); *os << " " << std::setw(indent) << ""; if (rep->tag == CONCAT) { *os << "CONCAT depth=" << Depth(rep) << "\n"; indent += kIndentStep; indents.push_back(indent); stack.push_back(rep->concat()->right); rep = rep->concat()->left; } else if (rep->tag == SUBSTRING) { *os << "SUBSTRING @ " << rep->substring()->start << "\n"; indent += kIndentStep; rep = rep->substring()->child; } else { // Leaf if (rep->tag == EXTERNAL) { *os << "EXTERNAL ["; if (include_data) *os << absl::CEscape(std::string(rep->external()->base, rep->length)); *os << "]\n"; } else { *os << "FLAT cap=" << TagToLength(rep->tag) << " ["; if (include_data) *os << absl::CEscape(std::string(rep->data, rep->length)); *os << "]\n"; } if (stack.empty()) break; rep = stack.back(); stack.pop_back(); indent = indents.back(); indents.pop_back(); } } ABSL_INTERNAL_CHECK(indents.empty(), ""); } static std::string ReportError(CordRep* root, CordRep* node) { std::ostringstream buf; buf << "Error at node " << node << " in:"; DumpNode(root, true, &buf); return buf.str(); } static bool VerifyNode(CordRep* root, CordRep* start_node, bool full_validation) { absl::InlinedVector<CordRep*, 2> worklist; worklist.push_back(start_node); do { CordRep* node = worklist.back(); worklist.pop_back(); ABSL_INTERNAL_CHECK(node != nullptr, ReportError(root, node)); if (node != root) { ABSL_INTERNAL_CHECK(node->length != 0, ReportError(root, node)); } if (node->tag == CONCAT) { ABSL_INTERNAL_CHECK(node->concat()->left != nullptr, ReportError(root, node)); ABSL_INTERNAL_CHECK(node->concat()->right != nullptr, ReportError(root, node)); ABSL_INTERNAL_CHECK((node->length == node->concat()->left->length + node->concat()->right->length), ReportError(root, node)); if (full_validation) { worklist.push_back(node->concat()->right); worklist.push_back(node->concat()->left); } } else if (node->tag >= FLAT) { ABSL_INTERNAL_CHECK(node->length <= TagToLength(node->tag), ReportError(root, node)); } else if (node->tag == EXTERNAL) { ABSL_INTERNAL_CHECK(node->external()->base != nullptr, ReportError(root, node)); } else if (node->tag == SUBSTRING) { ABSL_INTERNAL_CHECK( node->substring()->start < node->substring()->child->length, ReportError(root, node)); ABSL_INTERNAL_CHECK(node->substring()->start + node->length <= node->substring()->child->length, ReportError(root, node)); } } while (!worklist.empty()); return true; } // Traverses the tree and computes the total memory allocated. /* static */ size_t Cord::MemoryUsageAux(const CordRep* rep) { size_t total_mem_usage = 0; // Allow a quick exit for the common case that the root is a leaf. if (RepMemoryUsageLeaf(rep, &total_mem_usage)) { return total_mem_usage; } // Iterate over the tree. cur_node is never a leaf node and leaf nodes will // never be appended to tree_stack. This reduces overhead from manipulating // tree_stack. absl::InlinedVector<const CordRep*, kInlinedVectorSize> tree_stack; const CordRep* cur_node = rep; while (true) { const CordRep* next_node = nullptr; if (cur_node->tag == CONCAT) { total_mem_usage += sizeof(CordRepConcat); const CordRep* left = cur_node->concat()->left; if (!RepMemoryUsageLeaf(left, &total_mem_usage)) { next_node = left; } const CordRep* right = cur_node->concat()->right; if (!RepMemoryUsageLeaf(right, &total_mem_usage)) { if (next_node) { tree_stack.push_back(next_node); } next_node = right; } } else { // Since cur_node is not a leaf or a concat node it must be a substring. assert(cur_node->tag == SUBSTRING); total_mem_usage += sizeof(CordRepSubstring); next_node = cur_node->substring()->child; if (RepMemoryUsageLeaf(next_node, &total_mem_usage)) { next_node = nullptr; } } if (!next_node) { if (tree_stack.empty()) { return total_mem_usage; } next_node = tree_stack.back(); tree_stack.pop_back(); } cur_node = next_node; } } std::ostream& operator<<(std::ostream& out, const Cord& cord) { for (absl::string_view chunk : cord.Chunks()) { out.write(chunk.data(), chunk.size()); } return out; } namespace strings_internal { size_t CordTestAccess::FlatOverhead() { return kFlatOverhead; } size_t CordTestAccess::MaxFlatLength() { return kMaxFlatLength; } size_t CordTestAccess::FlatTagToLength(uint8_t tag) { return TagToLength(tag); } uint8_t CordTestAccess::LengthToTag(size_t s) { ABSL_INTERNAL_CHECK(s <= kMaxFlatLength, absl::StrCat("Invalid length ", s)); return AllocatedSizeToTag(s + kFlatOverhead); } size_t CordTestAccess::SizeofCordRepConcat() { return sizeof(CordRepConcat); } size_t CordTestAccess::SizeofCordRepExternal() { return sizeof(CordRepExternal); } size_t CordTestAccess::SizeofCordRepSubstring() { return sizeof(CordRepSubstring); } } // namespace strings_internal ABSL_NAMESPACE_END } // namespace absl