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Made findAllMatchesHelper non-recursive, added pruneIndices (improved performance) and more changes

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I made findAllMatchesHelper a non-recursive function. It now only
returns the first match it finds in the string (so I should probably
rename it).

These indices are collected by findAllMatches and pruned (to
remove overlaps). The overlap function has also been rewritten, to make
it (I believe) less than O(n^2). I also used the uniq_arr type to make
checking for uniqueness O(1) instaed of O(n) (as it was with
unique_append()). This has resulted in massive performance gains.

There's been a lot of changes here, and I probably haven't documented
all of them.
This commit is contained in:
Aadhavan Srinivasan
2024-11-07 16:16:50 -05:00
parent 9201ed49bd
commit 137ea3c746
1 changed files with 83 additions and 50 deletions
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133
matching.go
View File

@@ -1,25 +1,17 @@
package main
// a matchIndex represents a match. It contains the start index and end index of the match
type matchIndex struct {
import "sort"
// a MatchIndex represents a match/group. It contains the start index and end index of the match
type MatchIndex struct {
startIdx int
endIdx int
}
// Returns true if the given matchIndex has ovelrap with any of the indices in the slice.
// When we add an index to our slice, we want to make sure a larger match isn't already present.
func overlaps(idx matchIndex, idxes []matchIndex) bool {
for _, val := range idxes {
if (idx.startIdx > val.startIdx && idx.startIdx < val.endIdx) || (idx.endIdx > val.startIdx && idx.endIdx < val.endIdx) {
// A zero-length match doesn't overlap if it is located at the start or end
// of the other match
if !(idx.startIdx == idx.endIdx && (idx.startIdx == val.startIdx || idx.startIdx == val.endIdx)) {
return true
}
}
}
return false
}
// A Match represents multiple matchIndices. Specifically, it maps an integer (representing the capturing group)
// to the matchIndex of that group.
// Group 0 corresponds to the entire match.
type Match map[int]MatchIndex
// takeZeroState takes the 0-state (if such a transition exists) for all states in the
// given slice. It returns the resulting states. If any of the resulting states is a 0-state,
@@ -44,7 +36,7 @@ func takeZeroState(states []*State) (rtv []*State, isZero bool) {
// so I should probably put it in a function.
func zeroMatchPossible(states ...*State) bool {
zerostates, iszero := takeZeroState(states)
tempstates := make([]*State, 0)
tempstates := make([]*State, 0, len(zerostates)+len(states))
tempstates = append(tempstates, states...)
tempstates = append(tempstates, zerostates...)
num_appended := 0 // number of unique states addded to tempstates
@@ -63,15 +55,60 @@ func zeroMatchPossible(states ...*State) bool {
return false
}
// findAllMatches tries to findAllMatches the regex represented by given start-state, with
// the given string
func findAllMatches(start *State, str string) (indices []matchIndex) {
return findAllMatchesHelper(start, str, make([]matchIndex, 0), 0)
// Prunes the slice by removing overlapping indices.
func pruneIndices(indices []MatchIndex) []MatchIndex {
// First, sort the slice by the start indices
sort.Slice(indices, func(i, j int) bool {
return indices[i].startIdx < indices[j].startIdx
})
toRet := make([]MatchIndex, 0, len(indices))
current := indices[0]
for _, idx := range indices[1:] {
// idx doesn't overlap with current (starts after current ends), so add current to result
// and update the current.
if idx.startIdx >= current.endIdx {
toRet = append(toRet, current)
current = idx
} else if idx.endIdx > current.endIdx {
// idx overlaps, but it is longer, so update current
current = idx
}
}
// Add last state
toRet = append(toRet, current)
return toRet
}
func findAllMatchesHelper(start *State, str string, indices []matchIndex, offset int) []matchIndex {
// findAllMatches tries to find all matches of the regex represented by given start-state, with
// the given string
func findAllMatches(start *State, str string) []MatchIndex {
idx := 0
var matchFound bool
var matchIdx MatchIndex
indices := new_uniq_arr[MatchIndex]()
for idx <= len(str) {
matchFound, matchIdx, idx = findAllMatchesHelper(start, str, idx)
if matchFound {
indices.add(matchIdx)
}
}
toReturn := indices.values()
if len(toReturn) > 0 {
return pruneIndices(toReturn)
}
return toReturn
}
// Helper for findAllMatches. Returns whether it found a match, the
// first matchIndex it finds, and how far it got into the string ie. where
// the next search should start from.
//
// Might return duplicates or overlapping indices, so care must be taken to prune the resulting array.
func findAllMatchesHelper(start *State, str string, offset int) (bool, MatchIndex, int) {
// Base case - exit if offset exceeds string's length
if offset > len(str) {
return indices
// The first value here shouldn't be used, because we should exit when the second return value is > than len(str)
return false, MatchIndex{}, offset
}
// 'Base case' - if we are at the end of the string, check if we can add a zero-length match
if offset == len(str) {
@@ -79,12 +116,10 @@ func findAllMatchesHelper(start *State, str string, indices []matchIndex, offset
// can add a zero-length match. This is all true only if the start state itself matches nothing.
if start.isEmpty && start.assert == NONE {
if zeroMatchPossible(start) {
if !overlaps(matchIndex{offset, offset}, indices) {
indices, _ = unique_append(indices, matchIndex{offset, offset})
}
return true, MatchIndex{offset, offset}, offset + 1
}
}
return indices
return false, MatchIndex{}, offset + 1
}
foundPath := false
@@ -110,7 +145,7 @@ func findAllMatchesHelper(start *State, str string, indices []matchIndex, offset
// can no longer find a match, the match with the largest range is
// chosen as the match for the entire string.
// This allows us to pick the longest possible match (which is how greedy matching works).
tempIndices := make([]matchIndex, 0)
tempIndices := make([]MatchIndex, 0)
// Main loop
for i < len(str) {
foundPath = false
@@ -147,20 +182,19 @@ func findAllMatchesHelper(start *State, str string, indices []matchIndex, offset
}
if state.isLast {
endIdx = i
tempIndices, _ = unique_append(tempIndices, matchIndex{startIdx, endIdx})
tempIndices, _ = unique_append(tempIndices, MatchIndex{startIdx, endIdx})
}
}
if assertionFailed && numStatesMatched == 0 { // Nothing has matched and an assertion has failed - abort
if i == startingFrom {
i++
}
return findAllMatchesHelper(start, str, indices, i)
return false, MatchIndex{}, i
}
// Recursion - match with rest of string if we have nowhere to go.
// First check if we can find a zero-length match
// Check if we can find a zero-length match
if foundPath == false {
if zeroMatchPossible(currentStates...) {
tempIndices, _ = unique_append(tempIndices, matchIndex{startIdx, startIdx})
tempIndices, _ = unique_append(tempIndices, MatchIndex{startIdx, startIdx})
}
// If we haven't moved in the string, increment the counter by 1
// to ensure we don't keep trying the same string over and over.
@@ -169,9 +203,8 @@ func findAllMatchesHelper(start *State, str string, indices []matchIndex, offset
// i++
// }
// Get the maximum index-range from the list
end := 0
if len(tempIndices) > 0 {
indexToAdd := Reduce(tempIndices, func(i1 matchIndex, i2 matchIndex) matchIndex {
indexToAdd := Reduce(tempIndices, func(i1 MatchIndex, i2 MatchIndex) MatchIndex {
r1 := i1.endIdx - i1.startIdx
r2 := i2.endIdx - i2.startIdx
if r1 >= r2 {
@@ -179,16 +212,13 @@ func findAllMatchesHelper(start *State, str string, indices []matchIndex, offset
}
return i2
})
if !overlaps(indexToAdd, indices) {
indices, _ = unique_append(indices, indexToAdd)
end = indexToAdd.endIdx
if indexToAdd.startIdx == indexToAdd.endIdx { // If we have a zero-length match, we have to shift the index at which we start. Otherwise we keep looking at the same paert of the string over and over.
return true, indexToAdd, indexToAdd.endIdx + 1
} else {
return true, indexToAdd, indexToAdd.endIdx
}
}
if end == 0 || end == startIdx-1 { // Since we incremented startIdx earlier, we need to check against the old startIdx
return findAllMatchesHelper(start, str, indices, startIdx)
} else {
return findAllMatchesHelper(start, str, indices, end)
}
return false, MatchIndex{}, startIdx
}
currentStates = make([]*State, len(tempStates))
copy(currentStates, tempStates)
@@ -219,13 +249,13 @@ func findAllMatchesHelper(start *State, str string, indices []matchIndex, offset
if state.isLast && startIdx < len(str) {
if state.assert == NONE || state.checkAssertion(str, len(str)) {
endIdx = i
tempIndices, _ = unique_append(tempIndices, matchIndex{startIdx, endIdx})
tempIndices, _ = unique_append(tempIndices, MatchIndex{startIdx, endIdx})
}
}
}
// Get the maximum index-range from the list
if len(tempIndices) > 0 {
indexToAdd := Reduce(tempIndices, func(i1 matchIndex, i2 matchIndex) matchIndex {
indexToAdd := Reduce(tempIndices, func(i1 MatchIndex, i2 MatchIndex) MatchIndex {
r1 := i1.endIdx - i1.startIdx
r2 := i2.endIdx - i2.startIdx
if r1 >= r2 {
@@ -233,11 +263,14 @@ func findAllMatchesHelper(start *State, str string, indices []matchIndex, offset
}
return i2
})
if !overlaps(indexToAdd, indices) {
indices, _ = unique_append(indices, indexToAdd)
if indexToAdd.endIdx == indexToAdd.startIdx { // Same statement occurs above, see reasoning there
return true, indexToAdd, indexToAdd.endIdx + 1
} else {
return true, indexToAdd, indexToAdd.endIdx
}
}
// Default - call on empty string to get any trailing zero-length matches
return findAllMatchesHelper(start, str, indices, startIdx+1)
if startIdx == startingFrom { // Increment starting index if we haven't moved in the string. Prevents us from matching the same part of the string over and over.
startIdx++
}
return false, MatchIndex{}, startIdx
}