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671 lines (579 loc) · 22.1 KB
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// Copyright 2011 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef SRC_STRING_SEARCH_H_
#define SRC_STRING_SEARCH_H_
#include "node.h"
#include <string.h>
namespace node {
namespace stringsearch {
// Returns the maximum of the two parameters.
template <typename T>
T Max(T a, T b) {
return a < b ? b : a;
}
static const uint32_t kMaxOneByteCharCodeU = 0xff;
static inline size_t NonOneByteStart(const uint16_t* chars, size_t length) {
const uint16_t* limit = chars + length;
const uint16_t* start = chars;
while (chars < limit) {
if (*chars > kMaxOneByteCharCodeU)
return static_cast<size_t>(chars - start);
++chars;
}
return static_cast<size_t>(chars - start);
}
static inline bool IsOneByte(const uint16_t* chars, size_t length) {
return NonOneByteStart(chars, length) >= length;
}
template <typename T>
class Vector {
public:
Vector(T* data, size_t length) : start_(data), length_(length) {
ASSERT(length > 0 && data != nullptr);
}
// Returns the length of the vector.
size_t length() const { return length_; }
T* start() const { return start_; }
// Access individual vector elements - checks bounds in debug mode.
T& operator[](size_t index) const {
ASSERT(0 <= index && index < length_);
return start_[index];
}
const T& at(size_t index) const { return operator[](index); }
bool operator==(const Vector<T>& other) const {
if (length_ != other.length_)
return false;
<
10BC0
/div> if (start_ == other.start_)
return true;
for (size_t i = 0; i < length_; ++i) {
if (start_[i] != other.start_[i]) {
return false;
}
}
return true;
}
private:
T* start_;
size_t length_;
};
//---------------------------------------------------------------------
// String Search object.
//---------------------------------------------------------------------
// Class holding constants and methods that apply to all string search variants,
// independently of subject and pattern char size.
class StringSearchBase {
protected:
// Cap on the maximal shift in the Boyer-Moore implementation. By setting a
// limit, we can fix the size of tables. For a needle longer than this limit,
// search will not be optimal, since we only build tables for a suffix
// of the string, but it is a safe approximation.
static const int kBMMaxShift = 250;
// Reduce alphabet to this size.
// One of the tables used by Boyer-Moore and Boyer-Moore-Horspool has size
// proportional to the input alphabet. We reduce the alphabet size by
// equating input characters modulo a smaller alphabet size. This gives
// a potentially less efficient searching, but is a safe approximation.
// For needles using only characters in the same Unicode 256-code point page,
// there is no search speed degradation.
static const int kLatin1AlphabetSize = 256;
static const int kUC16AlphabetSize = 256;
// Bad-char shift table stored in the state. It's length is the alphabet size.
// For patterns below this length, the skip length of Boyer-Moore is too short
// to compensate for the algorithmic overhead compared to simple brute force.
static const int kBMMinPatternLength = 8;
// Store for the BoyerMoore(Horspool) bad char shift table.
static int kBadCharShiftTable[kUC16AlphabetSize];
// Store for the BoyerMoore good suffix shift table.
static int kGoodSuffixShiftTable[kBMMaxShift + 1];
// Table used temporarily while building the BoyerMoore good suffix
// shift table.
static int kSuffixTable[kBMMaxShift + 1];
static inline bool IsOneByteString(Vector<const uint8_t> string) {
return true;
}
static inline bool IsOneByteString(Vector<const uint16_t> string) {
return IsOneByte(string.start(), string.length());
}
};
template <typename PatternChar, typename SubjectChar>
class StringSearch : private StringSearchBase {
public:
explicit StringSearch(Vector<const PatternChar> pattern)
: pattern_(pattern), start_(0) {
if (pattern.length() >= kBMMaxShift) {
start_ = pattern.length() - kBMMaxShift;
}
if (sizeof(PatternChar) > sizeof(SubjectChar)) {
if (!IsOneByteString(pattern_)) {
strategy_ = &FailSearch;
return;
}
}
size_t pattern_length = pattern_.length();
CHECK_GT(pattern_length, 0);
if (pattern_length < kBMMinPatternLength) {
if (pattern_length == 1) {
strategy_ = &SingleCharSearch;
return;
}
strategy_ = &LinearSearch;
return;
}
strategy_ = &InitialSearch;
}
size_t Search(Vector<const SubjectChar> subject, size_t index) {
return strategy_(this, subject, index);
}
static inline int AlphabetSize() {
if (sizeof(PatternChar) == 1) {
// Latin1 needle.
return kLatin1AlphabetSize;
} else {
// UC16 needle.
return kUC16AlphabetSize;
}
static_assert(sizeof(PatternChar) == sizeof(uint8_t) ||
sizeof(PatternChar) == sizeof(uint16_t),
"sizeof(PatternChar) == sizeof(uint16_t) || sizeof(uint8_t)");
}
private:
typedef size_t (*SearchFunction)( // NOLINT - it's not a cast!
StringSearch<PatternChar, SubjectChar>*,
Vector<const SubjectChar>,
size_t);
static size_t FailSearch(StringSearch<PatternChar, SubjectChar>*,
Vector<const SubjectChar> subject,
size_t) {
return subject.length();
}
static size_t SingleCharSearch(StringSearch<PatternChar, SubjectChar>* search,
Vector<const SubjectChar> subject,
size_t start_index);
static size_t LinearSearch(StringSearch<PatternChar, SubjectChar>* search,
Vector<const SubjectChar> subject,
size_t start_index);
static size_t InitialSearch(StringSearch<PatternChar, SubjectChar>* search,
Vector<const SubjectChar> subject,
size_t start_index);
static size_t BoyerMooreHorspoolSearch(
StringSearch<PatternChar, SubjectChar>* search,
Vector<const SubjectChar> subject,
size_t start_index);
static size_t BoyerMooreSearch(StringSearch<PatternChar, SubjectChar>* search,
Vector<const SubjectChar> subject,
size_t start_index);
void PopulateBoyerMooreHorspoolTable();
void PopulateBoyerMooreTable();
static inline bool exceedsOneByte(uint8_t c) { return false; }
static inline bool exceedsOneByte(uint16_t c) {
return c > kMaxOneByteCharCodeU;
}
static inline int CharOccurrence(int* bad_char_occurrence,
SubjectChar char_code) {
if (sizeof(SubjectChar) == 1) {
return bad_char_occurrence[static_cast<int>(char_code)];
}
if (sizeof(PatternChar) == 1) {
if (exceedsOneByte(char_code)) {
return -1;
}
return bad_char_occurrence[static_cast<unsigned int>(char_code)];
}
// Both pattern and subject are UC16. Reduce character to equivalence class.
int equiv_class = char_code % kUC16AlphabetSize;
return bad_char_occurrence[equiv_class];
}
// Store for the BoyerMoore(Horspool) bad char shift table.
// Return a table covering the last kBMMaxShift+1 positions of
// pattern.
int* bad_char_table() { return kBadCharShiftTable; }
// Store for the BoyerMoore good suffix shift table.
int* good_suffix_shift_table() {
// Return biased pointer that maps the range [start_..pattern_.length()
// to the kGoodSuffixShiftTable array.
return kGoodSuffixShiftTable - start_;
}
// Table used temporarily while building the BoyerMoore good suffix
// shift table.
int* suffix_table() {
// Return biased pointer that maps the range [start_..pattern_.length()
// to the kSuffixTable array.
return kSuffixTable - start_;
}
// The pattern to search for.
Vector<const PatternChar> pattern_;
// Pointer to implementation of the search.
SearchFunction strategy_;
// Cache value of Max(0, pattern_length() - kBMMaxShift)
size_t start_;
};
template <typename T, typename U>
inline T AlignDown(T value, U alignment) {
return reinterpret_cast<T>(
(reinterpret_cast<uintptr_t>(value) & ~(alignment - 1)));
}
inline uint8_t GetHighestValueByte(uint16_t character) {
return Max(static_cast<uint8_t>(character & 0xFF),
static_cast<uint8_t>(character >> 8));
}
inline uint8_t GetHighestValueByte(uint8_t character) { return character; }
template <typename PatternChar, typename SubjectChar>
inline size_t FindFirstCharacter(Vector<const PatternChar> pattern,
Vector<const SubjectChar> subject, size_t index) {
const PatternChar pattern_first_char = pattern[0];
const size_t max_n = (subject.length() - pattern.length() + 1);
const uint8_t search_byte = GetHighestValueByte(pattern_first_char);
const SubjectChar search_char = static_cast<SubjectChar>(pattern_first_char);
size_t pos = index;
do {
const SubjectChar* char_pos = reinterpret_cast<const SubjectChar*>(
memchr(subject.start() + pos, search_byte,
(max_n - pos) * sizeof(SubjectChar)));
if (char_pos == nullptr)
return subject.length();
char_pos = AlignDown(char_pos, sizeof(SubjectChar));
pos = static_cast<size_t>(char_pos - subject.start());
if (subject[pos] == search_char)
return pos;
} while (++pos < max_n);
return subject.length();
}
template <>
inline size_t FindFirstCharacter(Vector<const uint8_t> pattern,
Vector<const uint8_t> subject,
size_t index) {
const uint8_t pattern_first_char = pattern[0];
const size_t max_n = (subject.length() - pattern.length() + 1);
const uint8_t* char_pos = reinterpret_cast<const uint8_t*>(
memchr(subject.start() + index, pattern_first_char, max_n - index));
if (char_pos == nullptr)
return subject.length();
return static_cast<size_t>(char_pos - subject.start());
}
//---------------------------------------------------------------------
// Single Character Pattern Search Strategy
//---------------------------------------------------------------------
template <typename PatternChar, typename SubjectChar>
size_t StringSearch<PatternChar, SubjectChar>::SingleCharSearch(
StringSearch<PatternChar, SubjectChar>* search,
Vector<const SubjectChar> subject,
size_t index) {
CHECK_EQ(1, search->pattern_.length());
PatternChar pattern_first_char = search->pattern_[0];
if (sizeof(SubjectChar) == 1 && sizeof(PatternChar) == 1) {
return FindFirstCharacter(search->pattern_, subject, index);
} else {
if (sizeof(PatternChar) > sizeof(SubjectChar)) {
if (exceedsOneByte(pattern_first_char)) {
return -1;
}
}
return FindFirstCharacter(search->pattern_, subject, index);
}
}
//---------------------------------------------------------------------
// Linear Search Strategy
//---------------------------------------------------------------------
template <typename PatternChar, typename SubjectChar>
inline bool CharCompare(const PatternChar* pattern,
const SubjectChar* subject,
size_t length) {
ASSERT_GT(length, 0);
size_t pos = 0;
do {
if (pattern[pos] != subject[pos]) {
return false;
}
pos++;
} while (pos < length);
return true;
}
// Simple linear search for short patterns. Never bails out.
template <typename PatternChar, typename SubjectChar>
size_t StringSearch<PatternChar, SubjectChar>::LinearSearch(
StringSearch<PatternChar, SubjectChar>* search,
Vector<const SubjectChar> subject,
size_t index) {
Vector<const PatternChar> pattern = search->pattern_;
CHECK_GT(pattern.length(), 1);
const size_t pattern_length = pattern.length();
size_t i = index;
const size_t n = subject.length() - pattern_length;
while (i <= n) {
i = FindFirstCharacter(pattern, subject, i);
if (i == subject.length())
return subject.length();
ASSERT_LE(i, n);
i++;
// Loop extracted to separate function to allow using return to do
// a deeper break.
if (CharCompare(pattern.start() + 1, subject.start() + i,
pattern_length - 1)) {
return i - 1;
}
}
return subject.length();
}
//---------------------------------------------------------------------
// Boyer-Moore string search
//---------------------------------------------------------------------
template <typename PatternChar, typename SubjectChar>
size_t StringSearch<PatternChar, SubjectChar>::BoyerMooreSearch(
StringSearch<PatternChar, SubjectChar>* search,
Vector<const SubjectChar> subject,
size_t start_index) {
Vector<const PatternChar> pattern = search->pattern_;
const size_t subject_length = subject.length();
const size_t pattern_length = pattern.length();
// Only preprocess at most kBMMaxShift last characters of pattern.
size_t start = search->start_;
int* bad_char_occurence = search->bad_char_table();
int* good_suffix_shift = search->good_suffix_shift_table();
PatternChar last_char = pattern[pattern_length - 1];
size_t index = start_index;
// Continue search from i.
while (index <= subject_length - pattern_length) {
size_t j = pattern_length - 1;
int c;
while (last_char != (c = subject[index + j])) {
int shift = j - CharOccurrence(bad_char_occurence, c);
index += shift;
if (index > subject_length - pattern_length) {
return subject.length();
}
}
while (j >= 0 && pattern[j] == (c = subject[index + j])) {
if (j == 0) {
return index;
}
j--;
}
if (j < start) {
// we have matched more than our tables allow us to be smart about.
// Fall back on BMH shift.
index += pattern_length - 1 -
CharOccurrence(bad_char_occurence,
static_cast<SubjectChar>(last_char));
} else {
int gs_shift = good_suffix_shift[j + 1];
int bc_occ = CharOccurrence(bad_char_occurence, c);
int shift = j - bc_occ;
if (gs_shift > shift) {
shift = gs_shift;
}
index += shift;
}
}
return subject.length();
}
template <typename PatternChar, typename SubjectChar>
void StringSearch<PatternChar, SubjectChar>::PopulateBoyerMooreTable() {
const size_t pattern_length = pattern_.length();
const PatternChar* pattern = pattern_.start();
// Only look at the last kBMMaxShift characters of pattern (from start_
// to pattern_length).
const size_t start = start_;
const size_t length = pattern_length - start;
// Biased tables so that we can use pattern indices as table indices,
// even if we only cover the part of the pattern from offset start.
int* shift_table = good_suffix_shift_table();
int* suffix_table = this->suffix_table();
// Initialize table.
for (size_t i = start; i < pattern_length; i++) {
shift_table[i] = length;
}
shift_table[pattern_length] = 1;
suffix_table[pattern_length] = pattern_length + 1;
if (pattern_length <= start) {
return;
}
// Find suffixes.
PatternChar last_char = pattern[pattern_length - 1];
size_t suffix = pattern_length + 1;
{
size_t i = pattern_length;
while (i > start) {
PatternChar c = pattern[i - 1];
while (suffix <= pattern_length && c != pattern[suffix - 1]) {
if (static_cast<size_t>(shift_table[suffix]) == length) {
shift_table[suffix] = suffix - i;
}
suffix = suffix_table[suffix];
}
suffix_table[--i] = --suffix;
if (suffix == pattern_length) {
// No suffix to extend, so we check against last_char only.
while ((i > start) && (pattern[i - 1] != last_char)) {
if (static_cast<size_t>(shift_table[pattern_length]) == length) {
shift_table[pattern_length] = pattern_length - i;
}
suffix_table[--i] = pattern_length;
}
if (i > start) {
suffix_table[--i] = --suffix;
}
}
}
}
// Build shift table using suffixes.
if (suffix < pattern_length) {
for (size_t i = start; i <= pattern_length; i++) {
if (static_cast<size_t>(shift_table[i]) == length) {
shift_table[i] = suffix - start;
}
if (i == suffix) {
suffix = suffix_table[suffix];
}
}
}
}
//---------------------------------------------------------------------
// Boyer-Moore-Horspool string search.
//---------------------------------------------------------------------
template <typename PatternChar, typename SubjectChar>
size_t StringSearch<PatternChar, SubjectChar>::BoyerMooreHorspoolSearch(
StringSearch<PatternChar, SubjectChar>* search,
Vector<const SubjectChar> subject,
size_t start_index) {
Vector<const PatternChar> pattern = search->pattern_;
const size_t subject_length = subject.length();
const size_t pattern_length = pattern.length();
int* char_occurrences = search->bad_char_table();
int64_t badness = -pattern_length;
// How bad we are doing without a good-suffix table.
PatternChar last_char = pattern[pattern_length - 1];
int last_char_shift =
pattern_length - 1 -
CharOccurrence(char_occurrences, static_cast<SubjectChar>(last_char));
// Perform search
size_t index = start_index; // No matches found prior to this index.
while (index <= subject_length - pattern_length) {
size_t j = pattern_length - 1;
int subject_char;
while (last_char != (subject_char = subject[index + j])) {
int bc_occ = CharOccurrence(char_occurrences, subject_char);
int shift = j - bc_occ;
index += shift;
badness += 1 - shift; // at most zero, so badness cannot increase.
if (index > subject_length - pattern_length) {
return subject_length;
}
}
j--;
while (j >= 0 && pattern[j] == (subject[index + j])) {
if (j == 0) {
return index;
}
j--;
}
index += last_char_shift;
// Badness increases by the number of characters we have
// checked, and decreases by the number of characters we
// can skip by shifting. It's a measure of how we are doing
// compared to reading each character exactly once.
badness += (pattern_length - j) - last_char_shift;
if (badness > 0) {
search->PopulateBoyerMooreTable();
search->strategy_ = &BoyerMooreSearch;
return BoyerMooreSearch(search, subject, index);
}
}
return subject.length();
}
template <typename PatternChar, typename SubjectChar>
void StringSearch<PatternChar, SubjectChar>::PopulateBoyerMooreHorspoolTable() {
const size_t pattern_length = pattern_.length();
int* bad_char_occurrence = bad_char_table();
// Only preprocess at most kBMMaxShift last characters of pattern.
const size_t start = start_;
// Run forwards to populate bad_char_table, so that *last* instance
// of character equivalence class is the one registered.
// Notice: Doesn't include the last character.
const size_t table_size = AlphabetSize();
if (start == 0) {
// All patterns less than kBMMaxShift in length.
memset(bad_char_occurrence, -1, table_size * sizeof(*bad_char_occurrence));
} else {
for (size_t i = 0; i < table_size; i++) {
bad_char_occurrence[i] = start - 1;
}
}
for (size_t i = start; i < pattern_length - 1; i++) {
PatternChar c = pattern_[i];
int bucket = (sizeof(PatternChar) == 1) ? c : c % AlphabetSize();
bad_char_occurrence[bucket] = i;
}
}
//---------------------------------------------------------------------
// Linear string search with bailout to BMH.
//---------------
79CD
------------------------------------------------------
// Simple linear search for short patterns, which bails out if the string
// isn't found very early in the subject. Upgrades to BoyerMooreHorspool.
template <typename PatternChar, typename SubjectChar>
size_t StringSearch<PatternChar, SubjectChar>::InitialSearch(
StringSearch<PatternChar, SubjectChar>* search,
Vector<const SubjectChar> subject,
size_t index) {
Vector<const PatternChar> pattern = search->pattern_;
const size_t pattern_length = pattern.length();
// Badness is a count of how much work we have done. When we have
// done enough work we decide it's probably worth switching to a better
// algorithm.
int64_t badness = -10 - (pattern_length << 2);
// We know our pattern is at least 2 characters, we cache the first so
// the common case of the first character not matching is faster.
for (size_t i = index, n = subject.length() - pattern_length; i <= n; i++) {
badness++;
if (badness <= 0) {
i = FindFirstCharacter(pattern, subject, i);
if (i == subject.length())
return subject.length();
ASSERT_LE(i, n);
size_t j = 1;
do {
if (pattern[j] != subject[i + j]) {
break;
}
j++;
} while (j < pattern_length);
if (j == pattern_length) {
return i;
}
badness += j;
} else {
search->PopulateBoyerMooreHorspoolTable();
search->strategy_ = &BoyerMooreHorspoolSearch;
return BoyerMooreHorspoolSearch(search, subject, i);
}
}
return subject.length();
}
// Perform a a single stand-alone search.
// If searching multiple times for the same pattern, a search
// object should be constructed once and the Search function then called
// for each search.
template <typename SubjectChar, typename PatternChar>
size_t SearchString(Vector<const SubjectChar> subject,
Vector<const PatternChar> pattern,
size_t start_index) {
StringSearch<PatternChar, SubjectChar> search(pattern);
return search.Search(subject, start_index);
}
}
} // namespace node::stringsearch
namespace node {
using node::stringsearch::Vector;
template <typename SubjectChar, typename PatternChar>
size_t SearchString(const SubjectChar* haystack,
size_t haystack_length,
const PatternChar* needle,
size_t needle_length,
size_t start_index) {
return node::stringsearch::SearchString(
Vector<const SubjectChar>(haystack, haystack_length),
Vector<const PatternChar>(needle, needle_length),
start_index);
}
} // namespace node
#endif // SRC_STRING_SEARCH_H_