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--
87cdfd6aa40941e116cd79ef70f9a7a8271db163 by Abseil Team <absl-team@google.com>:

Fix a typo in random.h API documentation.

PiperOrigin-RevId: 305176308

--
8a38e1df49a18a954daca3ce617fd69045ff4c19 by Derek Mauro <dmauro@google.com>:

Import GitHub #647: Allow external add_subdirectory for using GoogleTest

PiperOrigin-RevId: 305156797

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b1a2441536d4964fbe4e2329e74c322e6c41a4e6 by Gennadiy Rozental <rogeeff@google.com>:

temporary roll back.

PiperOrigin-RevId: 305149619

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c78767577264348d2f881893f9407aadfe73ab75 by CJ Johnson <johnsoncj@google.com>:

Rollback update to linux_clang-latest container while investigating
a compiler bug.

PiperOrigin-RevId: 304897689

--
3c6fd38f53d2e982569fdba4043f75271c7b5de4 by Derek Mauro <dmauro@google.com>:

Update linux_clang-latest container to one based on Ubuntu 18.04,
which has libstdc++-8.

PiperOrigin-RevId: 304885120
GitOrigin-RevId: 87cdfd6aa40941e116cd79ef70f9a7a8271db163
Change-Id: Iefa6efee93907ec0eecb8add804c5cc2f052b64d
pull/661/head
Abseil Team 5 years ago committed by Gennadiy Rozental
parent c01b9916e7
commit 73ea9a9572
5 changed files with 177 additions and 355 deletions
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  1. 3
      CMakeLists.txt
  2. 2
      absl/random/random.h
  3. 248
      absl/strings/cord.cc
  4. 232
      absl/strings/cord.h
  5. 47
      absl/strings/cord_test.cc

3
CMakeLists.txt
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@ -82,7 +82,8 @@ endif()
find_package(Threads REQUIRED)
option(ABSL_USE_EXTERNAL_GOOGLETEST
"If ON, abseil will assume that the targets for googletest are already provided by the including project folder. This makes sense when abseil is used with add_subproject." OFF)
"If ON, Abseil will assume that the targets for GoogleTest are already provided by the including project. This makes sense when Abseil is used with add_subproject." OFF)
option(ABSL_USE_GOOGLETEST_HEAD
"If ON, abseil will download HEAD from googletest at config time." OFF)

2
absl/random/random.h
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@ -109,7 +109,7 @@ ABSL_NAMESPACE_BEGIN
// absl::BitGen::max()
//
// Returns the largest possible value from this bit generator., and
// Returns the largest possible value from this bit generator.
// absl::BitGen::discard(num)
//

248
absl/strings/cord.cc
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@ -31,6 +31,7 @@
#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"
@ -132,14 +133,6 @@ inline const CordRepExternal* CordRep::external() const {
return static_cast<const CordRepExternal*>(this);
}
using CordTreeConstPath = CordTreePath<const CordRep*, MaxCordDepth()>;
// This type is used to store the list of pending nodes during re-balancing.
// Its maximum size is 2 * MaxCordDepth() because the tree has a maximum
// possible depth of MaxCordDepth() and every concat node along a tree path
// could theoretically be split during rebalancing.
using RebalancingStack = CordTreePath<CordRep*, 2 * MaxCordDepth()>;
} // namespace cord_internal
static const size_t kFlatOverhead = offsetof(CordRep, data);
@ -188,78 +181,64 @@ static constexpr size_t TagToLength(uint8_t tag) {
// Enforce that kMaxFlatSize maps to a well-known exact tag value.
static_assert(TagToAllocatedSize(224) == kMaxFlatSize, "Bad tag logic");
constexpr size_t Fibonacci(uint8_t n, const size_t a = 0, const size_t b = 1) {
return n == 0
? a
: n == 1 ? b
: Fibonacci(n - 1, b,
(a > (size_t(-1) - b)) ? size_t(-1) : a + b);
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) >= kMinLength[depth(t)]
// The node depth is allowed to become larger to reduce rebalancing
// for larger strings (see ShouldRebalance).
constexpr size_t kMinLength[] = {
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), Fibonacci(48), Fibonacci(49), Fibonacci(50), Fibonacci(51),
Fibonacci(52), Fibonacci(53), Fibonacci(54), Fibonacci(55), Fibonacci(56),
Fibonacci(57), Fibonacci(58), Fibonacci(59), Fibonacci(60), Fibonacci(61),
Fibonacci(62), Fibonacci(63), Fibonacci(64), Fibonacci(65), Fibonacci(66),
Fibonacci(67), Fibonacci(68), Fibonacci(69), Fibonacci(70), Fibonacci(71),
Fibonacci(72), Fibonacci(73), Fibonacci(74), Fibonacci(75), Fibonacci(76),
Fibonacci(77), Fibonacci(78), Fibonacci(79), Fibonacci(80), Fibonacci(81),
Fibonacci(82), Fibonacci(83), Fibonacci(84), Fibonacci(85), Fibonacci(86),
Fibonacci(87), Fibonacci(88), Fibonacci(89), Fibonacci(90), Fibonacci(91),
Fibonacci(92), Fibonacci(93), Fibonacci(94), Fibonacci(95)};
static_assert(sizeof(kMinLength) / sizeof(size_t) >=
(cord_internal::MaxCordDepth() + 1),
"Not enough elements in kMinLength array to cover all the "
"supported Cord depth(s)");
inline bool ShouldRebalance(const CordRep* node) {
if (node->tag != CONCAT) return false;
size_t node_depth = node->concat()->depth();
if (node_depth <= 15) return false;
// Rebalancing Cords is expensive, so we reduce how often rebalancing occurs
// by allowing shallow Cords to have twice the depth that the Fibonacci rule
// would otherwise imply. Deep Cords need to follow the rule more closely,
// however to ensure algorithm correctness. We implement this with linear
// interpolation. Cords of depth 16 are treated as though they have a depth
// of 16 * 1/2, and Cords of depth MaxCordDepth() interpolate to
// MaxCordDepth() * 1.
return node->length <
kMinLength[(node_depth * (cord_internal::MaxCordDepth() - 16)) /
(2 * cord_internal::MaxCordDepth() - 16 - node_depth)];
}
// Unlike root balancing condition this one is part of the re-balancing
// algorithm and has to be always matching against right depth for
// algorithm to be correct.
inline bool IsNodeBalanced(const CordRep* node) {
if (node->tag != CONCAT) return true;
size_t node_depth = node->concat()->depth();
return node->length >= kMinLength[node_depth];
// 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(const CordRep* rep, bool include_data, std::ostream* os);
static bool VerifyNode(const CordRep* root, const CordRep* start_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) {
@ -306,8 +285,7 @@ __attribute__((preserve_most))
static void UnrefInternal(CordRep* rep) {
assert(rep != nullptr);
cord_internal::RebalancingStack pending;
absl::InlinedVector<CordRep*, kInlinedVectorSize> pending;
while (true) {
if (rep->tag == CONCAT) {
CordRepConcat* rep_concat = rep->concat();
@ -389,11 +367,6 @@ static void SetConcatChildren(CordRepConcat* concat, CordRep* left,
concat->length = left->length + right->length;
concat->set_depth(1 + std::max(Depth(left), Depth(right)));
ABSL_INTERNAL_CHECK(concat->depth() <= cord_internal::MaxCordDepth(),
"Cord depth exceeds max");
ABSL_INTERNAL_CHECK(concat->length >= left->length, "Cord is too long");
ABSL_INTERNAL_CHECK(concat->length >= right->length, "Cord is too long");
}
// Create a concatenation of the specified nodes.
@ -419,7 +392,7 @@ static CordRep* RawConcat(CordRep* left, CordRep* right) {
static CordRep* Concat(CordRep* left, CordRep* right) {
CordRep* rep = RawConcat(left, right);
if (rep != nullptr && ShouldRebalance(rep)) {
if (rep != nullptr && !IsRootBalanced(rep)) {
rep = Rebalance(rep);
}
return VerifyTree(rep);
@ -714,14 +687,6 @@ void Cord::InlineRep::ClearSlow() {
memset(data_, 0, sizeof(data_));
}
inline Cord::InternalChunkIterator Cord::internal_chunk_begin() const {
return InternalChunkIterator(this);
}
inline Cord::InternalChunkRange Cord::InternalChunks() const {
return InternalChunkRange(this);
}
// --------------------------------------------------------------------
// Constructors and destructors
@ -918,7 +883,7 @@ void Cord::Prepend(absl::string_view src) {
static CordRep* RemovePrefixFrom(CordRep* node, size_t n) {
if (n >= node->length) return nullptr;
if (n == 0) return Ref(node);
cord_internal::CordTreeMutablePath rhs_stack;
absl::InlinedVector<CordRep*, kInlinedVectorSize> rhs_stack;
while (node->tag == CONCAT) {
assert(n <= node->length);
@ -959,7 +924,7 @@ static CordRep* RemovePrefixFrom(CordRep* node, size_t n) {
static CordRep* RemoveSuffixFrom(CordRep* node, size_t n) {
if (n >= node->length) return nullptr;
if (n == 0) return Ref(node);
absl::cord_internal::CordTreeMutablePath lhs_stack;
absl::InlinedVector<CordRep*, kInlinedVectorSize> lhs_stack;
bool inplace_ok = node->refcount.IsOne();
while (node->tag == CONCAT) {
@ -1030,7 +995,6 @@ void Cord::RemoveSuffix(size_t n) {
// Work item for NewSubRange().
struct SubRange {
SubRange() = default;
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.
@ -1039,11 +1003,8 @@ struct SubRange {
};
static CordRep* NewSubRange(CordRep* node, size_t pos, size_t n) {
cord_internal::CordTreeMutablePath results;
// The algorithm below in worst case scenario adds up to 3 nodes to the `todo`
// list, but we also pop one out on every cycle. If original tree has depth d
// todo list can grew up to 2*d in size.
cord_internal::CordTreePath<SubRange, 2 * cord_internal::MaxCordDepth()> todo;
absl::InlinedVector<CordRep*, kInlinedVectorSize> results;
absl::InlinedVector<SubRange, kInlinedVectorSize> todo;
todo.push_back(SubRange(node, pos, n));
do {
const SubRange& sr = todo.back();
@ -1080,7 +1041,7 @@ static CordRep* NewSubRange(CordRep* node, size_t pos, size_t n) {
}
} while (!todo.empty());
assert(results.size() == 1);
return results.back();
return results[0];
}
Cord Cord::Subcord(size_t pos, size_t new_size) const {
@ -1096,7 +1057,7 @@ Cord Cord::Subcord(size_t pos, size_t new_size) const {
} else if (new_size == 0) {
// We want to return empty subcord, so nothing to do.
} else if (new_size <= InlineRep::kMaxInline) {
Cord::InternalChunkIterator it = internal_chunk_begin();
Cord::ChunkIterator it = chunk_begin();
it.AdvanceBytes(pos);
char* dest = sub_cord.contents_.data_;
size_t remaining_size = new_size;
@ -1119,12 +1080,11 @@ Cord Cord::Subcord(size_t pos, size_t new_size) const {
class CordForest {
public:
explicit CordForest(size_t length) : root_length_(length), trees_({}) {}
explicit CordForest(size_t length)
: root_length_(length), trees_(kMinLengthSize, nullptr) {}
void Build(CordRep* cord_root) {
// We are adding up to two nodes to the `pending` list, but we also popping
// one, so the size of `pending` will never exceed `MaxCordDepth()`.
cord_internal::CordTreeMutablePath pending(cord_root);
std::vector<CordRep*> pending = {cord_root};
while (!pending.empty()) {
CordRep* node = pending.back();
@ -1136,20 +1096,21 @@ class CordForest {
}
CordRepConcat* concat_node = node->concat();
if (IsNodeBalanced(concat_node)) {
AddNode(node);
continue;
}
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;
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 {
Ref(concat_node->right);
Ref(concat_node->left);
Unref(concat_node);
AddNode(node);
}
}
}
@ -1181,7 +1142,7 @@ class CordForest {
// Collect together everything with which we will merge with node
int i = 0;
for (; node->length >= kMinLength[i + 1]; ++i) {
for (; node->length > min_length[i + 1]; ++i) {
auto& tree_at_i = trees_[i];
if (tree_at_i == nullptr) continue;
@ -1192,7 +1153,7 @@ class CordForest {
sum = AppendNode(node, sum);
// Insert sum into appropriate place in the forest
for (; sum->length >= kMinLength[i]; ++i) {
for (; sum->length >= min_length[i]; ++i) {
auto& tree_at_i = trees_[i];
if (tree_at_i == nullptr) continue;
@ -1200,7 +1161,7 @@ class CordForest {
tree_at_i = nullptr;
}
// kMinLength[0] == 1, which means sum->length >= kMinLength[0]
// min_length[0] == 1, which means sum->length >= min_length[0]
assert(i > 0);
trees_[i - 1] = sum;
}
@ -1233,7 +1194,9 @@ class CordForest {
}
size_t root_length_;
std::array<cord_internal::CordRep*, cord_internal::MaxCordDepth()> trees_;
// 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;
@ -1334,7 +1297,7 @@ inline absl::string_view Cord::InlineRep::FindFlatStartPiece() const {
inline int Cord::CompareSlowPath(absl::string_view rhs, size_t compared_size,
size_t size_to_compare) const {
auto advance = [](Cord::InternalChunkIterator* it, absl::string_view* chunk) {
auto advance = [](Cord::ChunkIterator* it, absl::string_view* chunk) {
if (!chunk->empty()) return true;
++*it;
if (it->bytes_remaining_ == 0) return false;
@ -1342,7 +1305,7 @@ inline int Cord::CompareSlowPath(absl::string_view rhs, size_t compared_size,
return true;
};
Cord::InternalChunkIterator lhs_it = internal_chunk_begin();
Cord::ChunkIterator lhs_it = chunk_begin();
// compared_size is inside first chunk.
absl::string_view lhs_chunk =
@ -1364,7 +1327,7 @@ inline int Cord::CompareSlowPath(absl::string_view rhs, size_t compared_size,
inline int Cord::CompareSlowPath(const Cord& rhs, size_t compared_size,
size_t size_to_compare) const {
auto advance = [](Cord::InternalChunkIterator* it, absl::string_view* chunk) {
auto advance = [](Cord::ChunkIterator* it, absl::string_view* chunk) {
if (!chunk->empty()) return true;
++*it;
if (it->bytes_remaining_ == 0) return false;
@ -1372,8 +1335,8 @@ inline int Cord::CompareSlowPath(const Cord& rhs, size_t compared_size,
return true;
};
Cord::InternalChunkIterator lhs_it = internal_chunk_begin();
Cord::InternalChunkIterator rhs_it = rhs.internal_chunk_begin();
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 =
@ -1507,9 +1470,7 @@ void Cord::CopyToArraySlowPath(char* dst) const {
}
}
template <typename StorageType>
Cord::GenericChunkIterator<StorageType>&
Cord::GenericChunkIterator<StorageType>::operator++() {
Cord::ChunkIterator& Cord::ChunkIterator::operator++() {
ABSL_HARDENING_ASSERT(bytes_remaining_ > 0 &&
"Attempted to iterate past `end()`");
assert(bytes_remaining_ >= current_chunk_.size());
@ -1549,8 +1510,7 @@ Cord::GenericChunkIterator<StorageType>::operator++() {
return *this;
}
template <typename StorageType>
Cord Cord::GenericChunkIterator<StorageType>::AdvanceAndReadBytes(size_t n) {
Cord Cord::ChunkIterator::AdvanceAndReadBytes(size_t n) {
ABSL_HARDENING_ASSERT(bytes_remaining_ >= n &&
"Attempted to iterate past `end()`");
Cord subcord;
@ -1664,8 +1624,7 @@ Cord Cord::GenericChunkIterator<StorageType>::AdvanceAndReadBytes(size_t n) {
return subcord;
}
template <typename StorageType>
void Cord::GenericChunkIterator<StorageType>::AdvanceBytesSlowPath(size_t n) {
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.
@ -1851,18 +1810,18 @@ absl::string_view Cord::FlattenSlowPath() {
}
}
static void DumpNode(const CordRep* rep, bool include_data, std::ostream* os) {
static void DumpNode(CordRep* rep, bool include_data, std::ostream* os) {
const int kIndentStep = 1;
int indent = 0;
cord_internal::CordTreeConstPath stack;
cord_internal::CordTreePath<int, cord_internal::MaxCordDepth()> indents;
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<const void*>(rep);
if (include_data) *os << static_cast<void*>(rep);
*os << "]";
*os << " " << (IsNodeBalanced(rep) ? 'b' : 'u');
*os << " " << (IsRootBalanced(rep) ? 'b' : 'u');
*os << " " << std::setw(indent) << "";
if (rep->tag == CONCAT) {
*os << "CONCAT depth=" << Depth(rep) << "\n";
@ -1883,7 +1842,7 @@ static void DumpNode(const CordRep* rep, bool include_data, std::ostream* os) {
} else {
*os << "FLAT cap=" << TagToLength(rep->tag) << " [";
if (include_data)
*os << absl::CEscape(absl::string_view(rep->data, rep->length));
*os << absl::CEscape(std::string(rep->data, rep->length));
*os << "]\n";
}
if (stack.empty()) break;
@ -1896,19 +1855,19 @@ static void DumpNode(const CordRep* rep, bool include_data, std::ostream* os) {
ABSL_INTERNAL_CHECK(indents.empty(), "");
}
static std::string ReportError(const CordRep* root, const CordRep* node) {
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(const CordRep* root, const CordRep* start_node,
static bool VerifyNode(CordRep* root, CordRep* start_node,
bool full_validation) {
cord_internal::CordTreeConstPath worklist;
absl::InlinedVector<CordRep*, 2> worklist;
worklist.push_back(start_node);
do {
const CordRep* node = worklist.back();
CordRep* node = worklist.back();
worklist.pop_back();
ABSL_INTERNAL_CHECK(node != nullptr, ReportError(root, node));
@ -1958,7 +1917,7 @@ static bool VerifyNode(const CordRep* root, const CordRep* start_node,
// 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.
cord_internal::CordTreeConstPath tree_stack;
absl::InlinedVector<const CordRep*, kInlinedVectorSize> tree_stack;
const CordRep* cur_node = rep;
while (true) {
const CordRep* next_node = nullptr;
@ -2005,9 +1964,6 @@ std::ostream& operator<<(std::ostream& out, const Cord& cord) {
return out;
}
template class Cord::GenericChunkIterator<cord_internal::CordTreeMutablePath>;
template class Cord::GenericChunkIterator<cord_internal::CordTreeDynamicPath>;
namespace strings_internal {
size_t CordTestAccess::FlatOverhead() { return kFlatOverhead; }
size_t CordTestAccess::MaxFlatLength() { return kMaxFlatLength; }

232
absl/strings/cord.h
Unescape View File

@ -123,132 +123,12 @@ H HashFragmentedCord(H, const Cord&);
// Additionally, the API provides iterator utilities to iterate through Cord
// data via chunks or character bytes.
//
namespace cord_internal {
// It's expensive to keep a Cord's tree perfectly balanced, so instead we keep
// trees approximately balanced. A tree node N of depth D(N) that contains a
// string of L(N) characters is considered balanced if L >= Fibonacci(D + 2).
// The "+ 2" is used to ensure that every balanced leaf node contains at least
// one character. Here we presume that
// Fibonacci(0) = 0
// Fibonacci(1) = 1
// Fibonacci(2) = 1
// Fibonacci(3) = 2
// ...
// The algorithm is based on paper by Hans Boehm et al:
// https://www.cs.rit.edu/usr/local/pub/jeh/courses/QUARTERS/FP/Labs/CedarRope/rope-paper.pdf
// In this paper authors shows that rebalancing based on cord forest of already
// balanced subtrees can be proven to never produce tree of depth larger than
// largest Fibonacci number representable in the same integral type as cord size
// For 64 bit integers this is the 93rd Fibonacci number. For 32 bit integrals
// this is 47th Fibonacci number.
constexpr size_t MaxCordDepth() { return sizeof(size_t) == 8 ? 93 : 47; }
// This class models fixed max size stack of CordRep pointers.
// The elements are being pushed back and popped from the back.
template <typename CordRepPtr, size_t N>
class CordTreePath {
public:
CordTreePath() {}
explicit CordTreePath(CordRepPtr root) { push_back(root); }
bool empty() const { return size_ == 0; }
size_t size() const { return size_; }
void clear() { size_ = 0; }
CordRepPtr back() { return data_[size_ - 1]; }
void pop_back() {
--size_;
assert(size_ < N);
}
void push_back(CordRepPtr elem) { data_[size_++] = elem; }
private:
CordRepPtr data_[N];
size_t size_ = 0;
};
// Fixed length container for mutable "path" in cord tree, which can hold any
// possible valid path in cord tree.
using CordTreeMutablePath = CordTreePath<CordRep*, MaxCordDepth()>;
// Variable length container for mutable "path" in cord tree. It starts with
// capacity for 15 elements and grow if necessary.
using CordTreeDynamicPath =
absl::InlinedVector<absl::cord_internal::CordRep*, 15>;
} // namespace cord_internal
// 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>;
//----------------------------------------------------------------------------
// Cord::GenericChunkIterator
//----------------------------------------------------------------------------
//
// A `Cord::GenericChunkIterator` provides an interface for the standard
// `Cord::ChunkIterator` as well as some private implementations.
template <typename StorageType>
class GenericChunkIterator {
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;
GenericChunkIterator() = default;
GenericChunkIterator& operator++();
GenericChunkIterator operator++(int);
bool operator==(const GenericChunkIterator& other) const;
bool operator!=(const GenericChunkIterator& other) const;
reference operator*() const;
pointer operator->() const;
friend class Cord;
friend class CharIterator;
private:
// Constructs a `begin()` iterator from `cord`.
explicit GenericChunkIterator(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.
cord_internal::CordRep* current_leaf_ = nullptr;
// The number of bytes left in the `Cord` over which we are iterating.
size_t bytes_remaining_ = 0;
StorageType stack_of_right_children_;
};
template <typename IteratorType>
class GenericChunkRange {
public:
explicit GenericChunkRange(const Cord* cord) : cord_(cord) {}
IteratorType begin() const { return IteratorType(cord_); }
IteratorType end() const { return IteratorType(); }
private:
const Cord* cord_;
};
public:
// Cord::Cord() Constructors
@ -464,8 +344,51 @@ class Cord {
// * The iterator keeps state that can grow for Cords that contain many
// nodes and are imbalanced due to sharing. Prefer to pass this type by
// const reference instead of by value.
using ChunkIterator =
GenericChunkIterator<cord_internal::CordTreeDynamicPath>;
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_;
};
// Cord::ChunkIterator::chunk_begin()
//
@ -504,7 +427,16 @@ class Cord {
//
// Implementation note: `ChunkRange` is simply a convenience wrapper over
// `Cord::chunk_begin()` and `Cord::chunk_end()`.
using ChunkRange = GenericChunkRange<ChunkIterator>;
class ChunkRange {
public:
explicit ChunkRange(const Cord* cord) : cord_(cord) {}
ChunkIterator begin() const;
ChunkIterator end() const;
private:
const Cord* cord_;
};
// Cord::Chunks()
//
@ -800,14 +732,6 @@ class Cord {
static bool GetFlatAux(absl::cord_internal::CordRep* rep,
absl::string_view* fragment);
// Iterators for use inside Cord implementation
using InternalChunkIterator =
GenericChunkIterator<cord_internal::CordTreeMutablePath>;
using InternalChunkRange = GenericChunkRange<InternalChunkIterator>;
InternalChunkIterator internal_chunk_begin() const;
InternalChunkRange InternalChunks() const;
// Helper for ForEachChunk()
static void ForEachChunkAux(
absl::cord_internal::CordRep* rep,
@ -842,11 +766,6 @@ class Cord {
void AppendImpl(C&& src);
};
extern template class Cord::GenericChunkIterator<
cord_internal::CordTreeMutablePath>;
extern template class Cord::GenericChunkIterator<
cord_internal::CordTreeDynamicPath>;
ABSL_NAMESPACE_END
} // namespace absl
@ -1186,9 +1105,7 @@ inline bool Cord::StartsWith(absl::string_view rhs) const {
return EqualsImpl(rhs, rhs_size);
}
template <typename StorageType>
inline Cord::GenericChunkIterator<StorageType>::GenericChunkIterator(
const Cord* cord)
inline Cord::ChunkIterator::ChunkIterator(const Cord* cord)
: bytes_remaining_(cord->size()) {
if (cord->empty()) return;
if (cord->contents_.is_tree()) {
@ -1199,50 +1116,37 @@ inline Cord::GenericChunkIterator<StorageType>::GenericChunkIterator(
}
}
template <typename StorageType>
inline Cord::GenericChunkIterator<StorageType>
Cord::GenericChunkIterator<StorageType>::operator++(int) {
GenericChunkIterator tmp(*this);
inline Cord::ChunkIterator Cord::ChunkIterator::operator++(int) {
ChunkIterator tmp(*this);
operator++();
return tmp;
}
template <typename StorageType>
inline bool Cord::GenericChunkIterator<StorageType>::operator==(
const GenericChunkIterator<StorageType>& other) const {
inline bool Cord::ChunkIterator::operator==(const ChunkIterator& other) const {
return bytes_remaining_ == other.bytes_remaining_;
}
template <typename StorageType>
inline bool Cord::GenericChunkIterator<StorageType>::operator!=(
const GenericChunkIterator<StorageType>& other) const {
inline bool Cord::ChunkIterator::operator!=(const ChunkIterator& other) const {
return !(*this == other);
}
template <typename StorageType>
inline typename Cord::GenericChunkIterator<StorageType>::reference
Cord::GenericChunkIterator<StorageType>::operator*() const {
inline Cord::ChunkIterator::reference Cord::ChunkIterator::operator*() const {
ABSL_HARDENING_ASSERT(bytes_remaining_ != 0);
return current_chunk_;
}
template <typename StorageType>
inline typename Cord::GenericChunkIterator<StorageType>::pointer
Cord::GenericChunkIterator<StorageType>::operator->() const {
inline Cord::ChunkIterator::pointer Cord::ChunkIterator::operator->() const {
ABSL_HARDENING_ASSERT(bytes_remaining_ != 0);
return &current_chunk_;
}
template <typename StorageType>
inline void Cord::GenericChunkIterator<StorageType>::RemoveChunkPrefix(
size_t n) {
inline void Cord::ChunkIterator::RemoveChunkPrefix(size_t n) {
assert(n < current_chunk_.size());
current_chunk_.remove_prefix(n);
bytes_remaining_ -= n;
}
template <typename StorageType>
inline void Cord::GenericChunkIterator<StorageType>::AdvanceBytes(size_t n) {
inline void Cord::ChunkIterator::AdvanceBytes(size_t n) {
if (ABSL_PREDICT_TRUE(n < current_chunk_.size())) {
RemoveChunkPrefix(n);
} else if (n != 0) {
@ -1256,6 +1160,14 @@ inline Cord::ChunkIterator Cord::chunk_begin() const {
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++() {

47
absl/strings/cord_test.cc
Unescape View File

@ -1403,53 +1403,6 @@ TEST(CordChunkIterator, Operations) {
VerifyChunkIterator(subcords, 128);
}
TEST(CordChunkIterator, MaxLengthFullTree) {
// Start with a 1-byte cord, and then double its length in a loop. We should
// be able to do this until the point where we would overflow size_t.
absl::Cord cord;
size_t size = 1;
AddExternalMemory("x", &cord);
EXPECT_EQ(cord.size(), size);
const int kCordLengthDoublingLimit = std::numeric_limits<size_t>::digits - 1;
for (int i = 0; i < kCordLengthDoublingLimit; ++i) {
cord.Prepend(absl::Cord(cord));
size <<= 1;
EXPECT_EQ(cord.size(), size);
auto chunk_it = cord.chunk_begin();
EXPECT_EQ(*chunk_it, "x");
}
EXPECT_DEATH_IF_SUPPORTED(
(cord.Prepend(absl::Cord(cord)), *cord.chunk_begin()),
"Cord is too long");
}
TEST(CordChunkIterator, MaxDepth) {
// By reusing nodes, it's possible in pathological cases to build a Cord that
// exceeds both the maximum permissible length and depth. In this case, the
// violation of the maximum depth is reported.
absl::Cord left_child;
AddExternalMemory("x", &left_child);
absl::Cord root = left_child;
for (int i = 0; i < absl::cord_internal::MaxCordDepth() - 2; ++i) {
size_t new_size = left_child.size() + root.size();
root.Prepend(left_child);
EXPECT_EQ(root.size(), new_size);
auto chunk_it = root.chunk_begin();
EXPECT_EQ(*chunk_it, "x");
std::swap(left_child, root);
}
EXPECT_DEATH_IF_SUPPORTED(root.Prepend(left_child), "Cord is too long");
}
TEST(CordCharIterator, Traits) {
static_assert(std::is_copy_constructible<absl::Cord::CharIterator>::value,
"");

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