SPIRV-Tools/source/comp/move_to_front.h
dan sinclair 5fc011b453
Move bit_stream, move_to_front and huffman_codec. (#1833)
bit_stream, move_to_front and huffman_codec are only used by
source/tools. Move into that directory to make the usage clearer.
2018-08-14 09:52:05 -04:00

385 lines
12 KiB
C++

// Copyright (c) 2017 Google Inc.
//
// 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
//
// http://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.
#ifndef SOURCE_COMP_MOVE_TO_FRONT_H_
#define SOURCE_COMP_MOVE_TO_FRONT_H_
#include <cassert>
#include <cstdint>
#include <map>
#include <set>
#include <unordered_map>
#include <vector>
namespace spvtools {
namespace comp {
// Log(n) move-to-front implementation. Implements the following functions:
// Insert - pushes value to the front of the mtf sequence
// (only unique values allowed).
// Remove - remove value from the sequence.
// ValueFromRank - access value by its 1-indexed rank in the sequence.
// RankFromValue - get the rank of the given value in the sequence.
// Accessing a value with ValueFromRank or RankFromValue moves the value to the
// front of the sequence (rank of 1).
//
// The implementation is based on an AVL-based order statistic tree. The tree
// is ordered by timestamps issued when values are inserted or accessed (recent
// values go to the left side of the tree, old values are gradually rotated to
// the right side).
//
// Terminology
// rank: 1-indexed rank showing how recently the value was inserted or accessed.
// node: handle used internally to access node data.
// size: size of the subtree of a node (including the node).
// height: distance from a node to the farthest leaf.
class MoveToFront {
public:
explicit MoveToFront(size_t reserve_capacity = 4) {
nodes_.reserve(reserve_capacity);
// Create NIL node.
nodes_.emplace_back(Node());
}
virtual ~MoveToFront() = default;
// Inserts value in the move-to-front sequence. Does nothing if the value is
// already in the sequence. Returns true if insertion was successful.
// The inserted value is placed at the front of the sequence (rank 1).
bool Insert(uint32_t value);
// Removes value from move-to-front sequence. Returns false iff the value
// was not found.
bool Remove(uint32_t value);
// Computes 1-indexed rank of value in the move-to-front sequence and moves
// the value to the front. Example:
// Before the call: 4 8 2 1 7
// RankFromValue(8) returns 2
// After the call: 8 4 2 1 7
// Returns true iff the value was found in the sequence.
bool RankFromValue(uint32_t value, uint32_t* rank);
// Returns value corresponding to a 1-indexed rank in the move-to-front
// sequence and moves the value to the front. Example:
// Before the call: 4 8 2 1 7
// ValueFromRank(2) returns 8
// After the call: 8 4 2 1 7
// Returns true iff the rank is within bounds [1, GetSize()].
bool ValueFromRank(uint32_t rank, uint32_t* value);
// Moves the value to the front of the sequence.
// Returns false iff value is not in the sequence.
bool Promote(uint32_t value);
// Returns true iff the move-to-front sequence contains the value.
bool HasValue(uint32_t value) const;
// Returns the number of elements in the move-to-front sequence.
uint32_t GetSize() const { return SizeOf(root_); }
protected:
// Internal tree data structure uses handles instead of pointers. Leaves and
// root parent reference a singleton under handle 0. Although dereferencing
// a null pointer is not possible, inappropriate access to handle 0 would
// cause an assertion. Handles are not garbage collected if value was
// deprecated
// with DeprecateValue(). But handles are recycled when a node is
// repositioned.
// Internal tree data structure node.
struct Node {
// Timestamp from a logical clock which updates every time the element is
// accessed through ValueFromRank or RankFromValue.
uint32_t timestamp = 0;
// The size of the node's subtree, including the node.
// SizeOf(LeftOf(node)) + SizeOf(RightOf(node)) + 1.
uint32_t size = 0;
// Handles to connected nodes.
uint32_t left = 0;
uint32_t right = 0;
uint32_t parent = 0;
// Distance to the farthest leaf.
// Leaves have height 0, real nodes at least 1.
uint32_t height = 0;
// Stored value.
uint32_t value = 0;
};
// Creates node and sets correct values. Non-NIL nodes should be created only
// through this function. If the node with this value has been created
// previously
// and since orphaned, reuses the old node instead of creating a new one.
uint32_t CreateNode(uint32_t timestamp, uint32_t value);
// Node accessor methods. Naming is designed to be similar to natural
// language as these functions tend to be used in sequences, for example:
// ParentOf(LeftestDescendentOf(RightOf(node)))
// Returns value of the node referenced by |handle|.
uint32_t ValueOf(uint32_t node) const { return nodes_.at(node).value; }
// Returns left child of |node|.
uint32_t LeftOf(uint32_t node) const { return nodes_.at(node).left; }
// Returns right child of |node|.
uint32_t RightOf(uint32_t node) const { return nodes_.at(node).right; }
// Returns parent of |node|.
uint32_t ParentOf(uint32_t node) const { return nodes_.at(node).parent; }
// Returns timestamp of |node|.
uint32_t TimestampOf(uint32_t node) const {
assert(node);
return nodes_.at(node).timestamp;
}
// Returns size of |node|.
uint32_t SizeOf(uint32_t node) const { return nodes_.at(node).size; }
// Returns height of |node|.
uint32_t HeightOf(uint32_t node) const { return nodes_.at(node).height; }
// Returns mutable reference to value of |node|.
uint32_t& MutableValueOf(uint32_t node) {
assert(node);
return nodes_.at(node).value;
}
// Returns mutable reference to handle of left child of |node|.
uint32_t& MutableLeftOf(uint32_t node) {
assert(node);
return nodes_.at(node).left;
}
// Returns mutable reference to handle of right child of |node|.
uint32_t& MutableRightOf(uint32_t node) {
assert(node);
return nodes_.at(node).right;
}
// Returns mutable reference to handle of parent of |node|.
uint32_t& MutableParentOf(uint32_t node) {
assert(node);
return nodes_.at(node).parent;
}
// Returns mutable reference to timestamp of |node|.
uint32_t& MutableTimestampOf(uint32_t node) {
assert(node);
return nodes_.at(node).timestamp;
}
// Returns mutable reference to size of |node|.
uint32_t& MutableSizeOf(uint32_t node) {
assert(node);
return nodes_.at(node).size;
}
// Returns mutable reference to height of |node|.
uint32_t& MutableHeightOf(uint32_t node) {
assert(node);
return nodes_.at(node).height;
}
// Returns true iff |node| is left child of its parent.
bool IsLeftChild(uint32_t node) const {
assert(node);
return LeftOf(ParentOf(node)) == node;
}
// Returns true iff |node| is right child of its parent.
bool IsRightChild(uint32_t node) const {
assert(node);
return RightOf(ParentOf(node)) == node;
}
// Returns true iff |node| has no relatives.
bool IsOrphan(uint32_t node) const {
assert(node);
return !ParentOf(node) && !LeftOf(node) && !RightOf(node);
}
// Returns true iff |node| is in the tree.
bool IsInTree(uint32_t node) const {
assert(node);
return node == root_ || !IsOrphan(node);
}
// Returns the height difference between right and left subtrees.
int BalanceOf(uint32_t node) const {
return int(HeightOf(RightOf(node))) - int(HeightOf(LeftOf(node)));
}
// Updates size and height of the node, assuming that the children have
// correct values.
void UpdateNode(uint32_t node);
// Returns the most LeftOf(LeftOf(... descendent which is not leaf.
uint32_t LeftestDescendantOf(uint32_t node) const {
uint32_t parent = 0;
while (node) {
parent = node;
node = LeftOf(node);
}
return parent;
}
// Returns the most RightOf(RightOf(... descendent which is not leaf.
uint32_t RightestDescendantOf(uint32_t node) const {
uint32_t parent = 0;
while (node) {
parent = node;
node = RightOf(node);
}
return parent;
}
// Inserts node in the tree. The node must be an orphan.
void InsertNode(uint32_t node);
// Removes node from the tree. May change value_to_node_ if removal uses a
// scapegoat. Returns the removed (orphaned) handle for recycling. The
// returned handle may not be equal to |node| if scapegoat was used.
uint32_t RemoveNode(uint32_t node);
// Rotates |node| left, reassigns all connections and returns the node
// which takes place of the |node|.
uint32_t RotateLeft(const uint32_t node);
// Rotates |node| right, reassigns all connections and returns the node
// which takes place of the |node|.
uint32_t RotateRight(const uint32_t node);
// Root node handle. The tree is empty if root_ is 0.
uint32_t root_ = 0;
// Incremented counters for next timestamp and value.
uint32_t next_timestamp_ = 1;
// Holds all tree nodes. Indices of this vector are node handles.
std::vector<Node> nodes_;
// Maps ids to node handles.
std::unordered_map<uint32_t, uint32_t> value_to_node_;
// Cache for the last accessed value in the sequence.
uint32_t last_accessed_value_ = 0;
bool last_accessed_value_valid_ = false;
};
class MultiMoveToFront {
public:
// Inserts |value| to sequence with handle |mtf|.
// Returns false if |mtf| already has |value|.
bool Insert(uint64_t mtf, uint32_t value) {
if (GetMtf(mtf).Insert(value)) {
val_to_mtfs_[value].insert(mtf);
return true;
}
return false;
}
// Removes |value| from sequence with handle |mtf|.
// Returns false if |mtf| doesn't have |value|.
bool Remove(uint64_t mtf, uint32_t value) {
if (GetMtf(mtf).Remove(value)) {
val_to_mtfs_[value].erase(mtf);
return true;
}
assert(val_to_mtfs_[value].count(mtf) == 0);
return false;
}
// Removes |value| from all sequences which have it.
void RemoveFromAll(uint32_t value) {
auto it = val_to_mtfs_.find(value);
if (it == val_to_mtfs_.end()) return;
auto& mtfs_containing_value = it->second;
for (uint64_t mtf : mtfs_containing_value) {
GetMtf(mtf).Remove(value);
}
val_to_mtfs_.erase(value);
}
// Computes rank of |value| in sequence |mtf|.
// Returns false if |mtf| doesn't have |value|.
bool RankFromValue(uint64_t mtf, uint32_t value, uint32_t* rank) {
return GetMtf(mtf).RankFromValue(value, rank);
}
// Finds |value| with |rank| in sequence |mtf|.
// Returns false if |rank| is out of bounds.
bool ValueFromRank(uint64_t mtf, uint32_t rank, uint32_t* value) {
return GetMtf(mtf).ValueFromRank(rank, value);
}
// Returns size of |mtf| sequence.
uint32_t GetSize(uint64_t mtf) { return GetMtf(mtf).GetSize(); }
// Promotes |value| in all sequences which have it.
void Promote(uint32_t value) {
const auto it = val_to_mtfs_.find(value);
if (it == val_to_mtfs_.end()) return;
const auto& mtfs_containing_value = it->second;
for (uint64_t mtf : mtfs_containing_value) {
GetMtf(mtf).Promote(value);
}
}
// Inserts |value| in sequence |mtf| or promotes if it's already there.
void InsertOrPromote(uint64_t mtf, uint32_t value) {
if (!Insert(mtf, value)) {
GetMtf(mtf).Promote(value);
}
}
// Returns if |mtf| sequence has |value|.
bool HasValue(uint64_t mtf, uint32_t value) {
return GetMtf(mtf).HasValue(value);
}
private:
// Returns actual MoveToFront object corresponding to |handle|.
// As multiple operations are often performed consecutively for the same
// sequence, the last returned value is cached.
MoveToFront& GetMtf(uint64_t handle) {
if (!cached_mtf_ || cached_handle_ != handle) {
cached_handle_ = handle;
cached_mtf_ = &mtfs_[handle];
}
return *cached_mtf_;
}
// Container holding MoveToFront objects. Map key is sequence handle.
std::map<uint64_t, MoveToFront> mtfs_;
// Container mapping value to sequences which contain that value.
std::unordered_map<uint32_t, std::set<uint64_t>> val_to_mtfs_;
// Cache for the last accessed sequence.
uint64_t cached_handle_ = 0;
MoveToFront* cached_mtf_ = nullptr;
};
} // namespace comp
} // namespace spvtools
#endif // SOURCE_COMP_MOVE_TO_FRONT_H_