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-rw-r--r--absl/strings/cord.cc249
1 files changed, 127 insertions, 122 deletions
diff --git a/absl/strings/cord.cc b/absl/strings/cord.cc
index 415b239b..4f64f799 100644
--- a/absl/strings/cord.cc
+++ b/absl/strings/cord.cc
@@ -30,6 +30,7 @@
#include "absl/base/internal/raw_logging.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"
@@ -131,14 +132,6 @@ 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);
@@ -187,78 +180,98 @@ 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) {
@@ -305,8 +318,7 @@ __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();
@@ -388,11 +400,6 @@ 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.
@@ -418,7 +425,7 @@ 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);
@@ -909,7 +916,7 @@ 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);
@@ -950,7 +957,7 @@ 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) {
@@ -1021,7 +1028,6 @@ 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.
@@ -1030,11 +1036,8 @@ 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();
@@ -1071,7 +1074,7 @@ 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 {
@@ -1110,12 +1113,11 @@ 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();
@@ -1127,20 +1129,21 @@ 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);
}
}
}
@@ -1172,7 +1175,7 @@ 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;
@@ -1183,7 +1186,7 @@ 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;
@@ -1191,7 +1194,7 @@ 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;
}
@@ -1224,7 +1227,9 @@ 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;
@@ -1836,18 +1841,18 @@ 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";
@@ -1868,7 +1873,7 @@ 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;
@@ -1881,19 +1886,19 @@ 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));
@@ -1943,7 +1948,7 @@ 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;
generated by cgit v1.2.3 (git 2.39.1) at 2024-06-13 22:19:09 +0000