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//===- llvm/Support/SuffixTree.cpp - Implement Suffix Tree ------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements the Suffix Tree class.
//
//===----------------------------------------------------------------------===//
#include "llvm/Support/SuffixTree.h"
#include "llvm/Support/Allocator.h"
#include <vector>
using namespace llvm;
SuffixTree::SuffixTree(const std::vector<unsigned> &Str) : Str(Str) {
Root = insertInternalNode(nullptr, EmptyIdx, EmptyIdx, 0);
Active.Node = Root;
// Keep track of the number of suffixes we have to add of the current
// prefix.
unsigned SuffixesToAdd = 0;
// Construct the suffix tree iteratively on each prefix of the string.
// PfxEndIdx is the end index of the current prefix.
// End is one past the last element in the string.
for (unsigned PfxEndIdx = 0, End = Str.size(); PfxEndIdx < End; PfxEndIdx++) {
SuffixesToAdd++;
LeafEndIdx = PfxEndIdx; // Extend each of the leaves.
SuffixesToAdd = extend(PfxEndIdx, SuffixesToAdd);
}
// Set the suffix indices of each leaf.
assert(Root && "Root node can't be nullptr!");
setSuffixIndices();
}
SuffixTreeNode *SuffixTree::insertLeaf(SuffixTreeNode &Parent,
unsigned StartIdx, unsigned Edge) {
assert(StartIdx <= LeafEndIdx && "String can't start after it ends!");
SuffixTreeNode *N = new (NodeAllocator.Allocate())
SuffixTreeNode(StartIdx, &LeafEndIdx, nullptr);
Parent.Children[Edge] = N;
return N;
}
SuffixTreeNode *SuffixTree::insertInternalNode(SuffixTreeNode *Parent,
unsigned StartIdx,
unsigned EndIdx, unsigned Edge) {
assert(StartIdx <= EndIdx && "String can't start after it ends!");
assert(!(!Parent && StartIdx != EmptyIdx) &&
"Non-root internal nodes must have parents!");
unsigned *E = new (InternalEndIdxAllocator) unsigned(EndIdx);
SuffixTreeNode *N =
new (NodeAllocator.Allocate()) SuffixTreeNode(StartIdx, E, Root);
if (Parent)
Parent->Children[Edge] = N;
return N;
}
void SuffixTree::setSuffixIndices() {
// List of nodes we need to visit along with the current length of the
// string.
std::vector<std::pair<SuffixTreeNode *, unsigned>> ToVisit;
// Current node being visited.
SuffixTreeNode *CurrNode = Root;
// Sum of the lengths of the nodes down the path to the current one.
unsigned CurrNodeLen = 0;
ToVisit.push_back({CurrNode, CurrNodeLen});
while (!ToVisit.empty()) {
std::tie(CurrNode, CurrNodeLen) = ToVisit.back();
ToVisit.pop_back();
CurrNode->ConcatLen = CurrNodeLen;
for (auto &ChildPair : CurrNode->Children) {
assert(ChildPair.second && "Node had a null child!");
ToVisit.push_back(
{ChildPair.second, CurrNodeLen + ChildPair.second->size()});
}
// No children, so we are at the end of the string.
if (CurrNode->Children.size() == 0 && !CurrNode->isRoot())
CurrNode->SuffixIdx = Str.size() - CurrNodeLen;
}
}
unsigned SuffixTree::extend(unsigned EndIdx, unsigned SuffixesToAdd) {
SuffixTreeNode *NeedsLink = nullptr;
while (SuffixesToAdd > 0) {
// Are we waiting to add anything other than just the last character?
if (Active.Len == 0) {
// If not, then say the active index is the end index.
Active.Idx = EndIdx;
}
assert(Active.Idx <= EndIdx && "Start index can't be after end index!");
// The first character in the current substring we're looking at.
unsigned FirstChar = Str[Active.Idx];
// Have we inserted anything starting with FirstChar at the current node?
if (Active.Node->Children.count(FirstChar) == 0) {
// If not, then we can just insert a leaf and move to the next step.
insertLeaf(*Active.Node, EndIdx, FirstChar);
// The active node is an internal node, and we visited it, so it must
// need a link if it doesn't have one.
if (NeedsLink) {
NeedsLink->Link = Active.Node;
NeedsLink = nullptr;
}
} else {
// There's a match with FirstChar, so look for the point in the tree to
// insert a new node.
SuffixTreeNode *NextNode = Active.Node->Children[FirstChar];
unsigned SubstringLen = NextNode->size();
// Is the current suffix we're trying to insert longer than the size of
// the child we want to move to?
if (Active.Len >= SubstringLen) {
// If yes, then consume the characters we've seen and move to the next
// node.
Active.Idx += SubstringLen;
Active.Len -= SubstringLen;
Active.Node = NextNode;
continue;
}
// Otherwise, the suffix we're trying to insert must be contained in the
// next node we want to move to.
unsigned LastChar = Str[EndIdx];
// Is the string we're trying to insert a substring of the next node?
if (Str[NextNode->StartIdx + Active.Len] == LastChar) {
// If yes, then we're done for this step. Remember our insertion point
// and move to the next end index. At this point, we have an implicit
// suffix tree.
if (NeedsLink && !Active.Node->isRoot()) {
NeedsLink->Link = Active.Node;
NeedsLink = nullptr;
}
Active.Len++;
break;
}
// The string we're trying to insert isn't a substring of the next node,
// but matches up to a point. Split the node.
//
// For example, say we ended our search at a node n and we're trying to
// insert ABD. Then we'll create a new node s for AB, reduce n to just
// representing C, and insert a new leaf node l to represent d. This
// allows us to ensure that if n was a leaf, it remains a leaf.
//
// | ABC ---split---> | AB
// n s
// C / \ D
// n l
// The node s from the diagram
SuffixTreeNode *SplitNode =
insertInternalNode(Active.Node, NextNode->StartIdx,
NextNode->StartIdx + Active.Len - 1, FirstChar);
// Insert the new node representing the new substring into the tree as
// a child of the split node. This is the node l from the diagram.
insertLeaf(*SplitNode, EndIdx, LastChar);
// Make the old node a child of the split node and update its start
// index. This is the node n from the diagram.
NextNode->StartIdx += Active.Len;
SplitNode->Children[Str[NextNode->StartIdx]] = NextNode;
// SplitNode is an internal node, update the suffix link.
if (NeedsLink)
NeedsLink->Link = SplitNode;
NeedsLink = SplitNode;
}
// We've added something new to the tree, so there's one less suffix to
// add.
SuffixesToAdd--;
if (Active.Node->isRoot()) {
if (Active.Len > 0) {
Active.Len--;
Active.Idx = EndIdx - SuffixesToAdd + 1;
}
} else {
// Start the next phase at the next smallest suffix.
Active.Node = Active.Node->Link;
}
}
return SuffixesToAdd;
}
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