// Copyright 2003-2009 The RE2 Authors.  All Rights Reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Regular expression interface RE2.
//
// Originally the PCRE C++ wrapper, but adapted to use
// the new automata-based regular expression engines.

#include "re2/re2.h"

#include <assert.h>
#include <ctype.h>
#include <errno.h>
#ifdef _MSC_VER
#include <intrin.h>
#endif
#include <algorithm>
#include <atomic>
#include <iterator>
#include <mutex>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <string>
#include <utility>
#include <vector>

#include "re2/prog.h"
#include "re2/regexp.h"
#include "re2/sparse_array.h"
#include "util/logging.h"
#include "util/strutil.h"
#include "util/utf.h"
#include "util/util.h"

namespace re2 {

// Controls the maximum count permitted by GlobalReplace(); -1 is unlimited.
static int maximum_global_replace_count = -1;

void RE2::FUZZING_ONLY_set_maximum_global_replace_count(int i) { maximum_global_replace_count = i; }

// Maximum number of args we can set
static const int kMaxArgs = 16;
static const int kVecSize = 1 + kMaxArgs;

const int RE2::Options::kDefaultMaxMem; // initialized in re2.h

RE2::Options::Options(RE2::CannedOptions opt)
    : max_mem_(kDefaultMaxMem), encoding_(opt == RE2::Latin1 ? EncodingLatin1 : EncodingUTF8), posix_syntax_(opt == RE2::POSIX),
      longest_match_(opt == RE2::POSIX), log_errors_(opt != RE2::Quiet), literal_(false), never_nl_(false), dot_nl_(false), never_capture_(false),
      case_sensitive_(true), perl_classes_(false), word_boundary_(false), one_line_(false) {}

// Empty objects for use as const references.
// Statically allocating the storage and then
// lazily constructing the objects (in a once
// in RE2::Init()) avoids global constructors
// and the false positives (thanks, Valgrind)
// about memory leaks at program termination.
struct EmptyStorage {
    std::string empty_string;
    std::map<std::string, int> empty_named_groups;
    std::map<int, std::string> empty_group_names;
};
alignas(EmptyStorage) static char empty_storage[sizeof(EmptyStorage)];

static inline std::string *empty_string() { return &reinterpret_cast<EmptyStorage *>(empty_storage)->empty_string; }

static inline std::map<std::string, int> *empty_named_groups() { return &reinterpret_cast<EmptyStorage *>(empty_storage)->empty_named_groups; }

static inline std::map<int, std::string> *empty_group_names() { return &reinterpret_cast<EmptyStorage *>(empty_storage)->empty_group_names; }

// Converts from Regexp error code to RE2 error code.
// Maybe some day they will diverge.  In any event, this
// hides the existence of Regexp from RE2 users.
static RE2::ErrorCode RegexpErrorToRE2(re2::RegexpStatusCode code) {
    switch (code) {
        case re2::kRegexpSuccess:
            return RE2::NoError;
        case re2::kRegexpInternalError:
            return RE2::ErrorInternal;
        case re2::kRegexpBadEscape:
            return RE2::ErrorBadEscape;
        case re2::kRegexpBadCharClass:
            return RE2::ErrorBadCharClass;
        case re2::kRegexpBadCharRange:
            return RE2::ErrorBadCharRange;
        case re2::kRegexpMissingBracket:
            return RE2::ErrorMissingBracket;
        case re2::kRegexpMissingParen:
            return RE2::ErrorMissingParen;
        case re2::kRegexpUnexpectedParen:
            return RE2::ErrorUnexpectedParen;
        case re2::kRegexpTrailingBackslash:
            return RE2::ErrorTrailingBackslash;
        case re2::kRegexpRepeatArgument:
            return RE2::ErrorRepeatArgument;
        case re2::kRegexpRepeatSize:
            return RE2::ErrorRepeatSize;
        case re2::kRegexpRepeatOp:
            return RE2::ErrorRepeatOp;
        case re2::kRegexpBadPerlOp:
            return RE2::ErrorBadPerlOp;
        case re2::kRegexpBadUTF8:
            return RE2::ErrorBadUTF8;
        case re2::kRegexpBadNamedCapture:
            return RE2::ErrorBadNamedCapture;
    }
    return RE2::ErrorInternal;
}

static std::string trunc(const StringPiece &pattern) {
    if (pattern.size() < 100)
        return std::string(pattern);
    return std::string(pattern.substr(0, 100)) + "...";
}

RE2::RE2(const char *pattern) { Init(pattern, DefaultOptions); }

RE2::RE2(const std::string &pattern) { Init(pattern, DefaultOptions); }

RE2::RE2(const StringPiece &pattern) { Init(pattern, DefaultOptions); }

RE2::RE2(const StringPiece &pattern, const Options &options) { Init(pattern, options); }

int RE2::Options::ParseFlags() const {
    int flags = Regexp::ClassNL;
    switch (encoding()) {
        default:
            if (log_errors())
                LOG(ERROR) << "Unknown encoding " << encoding();
            break;
        case RE2::Options::EncodingUTF8:
            break;
        case RE2::Options::EncodingLatin1:
            flags |= Regexp::Latin1;
            break;
    }

    if (!posix_syntax())
        flags |= Regexp::LikePerl;

    if (literal())
        flags |= Regexp::Literal;

    if (never_nl())
        flags |= Regexp::NeverNL;

    if (dot_nl())
        flags |= Regexp::DotNL;

    if (never_capture())
        flags |= Regexp::NeverCapture;

    if (!case_sensitive())
        flags |= Regexp::FoldCase;

    if (perl_classes())
        flags |= Regexp::PerlClasses;

    if (word_boundary())
        flags |= Regexp::PerlB;

    if (one_line())
        flags |= Regexp::OneLine;

    return flags;
}

void RE2::Init(const StringPiece &pattern, const Options &options) {
    static std::once_flag empty_once;
    std::call_once(empty_once, []() { (void)new (empty_storage) EmptyStorage; });

    pattern_ = new std::string(pattern);
    options_.Copy(options);
    entire_regexp_ = NULL;
    suffix_regexp_ = NULL;
    error_ = empty_string();
    error_arg_ = empty_string();

    num_captures_ = -1;
    error_code_ = NoError;
    longest_match_ = options_.longest_match();
    is_one_pass_ = false;
    prefix_foldcase_ = false;
    prefix_.clear();
    prog_ = NULL;

    rprog_ = NULL;
    named_groups_ = NULL;
    group_names_ = NULL;

    RegexpStatus status;
    entire_regexp_ = Regexp::Parse(*pattern_, static_cast<Regexp::ParseFlags>(options_.ParseFlags()), &status);
    if (entire_regexp_ == NULL) {
        if (options_.log_errors()) {
            LOG(ERROR) << "Error parsing '" << trunc(*pattern_) << "': " << status.Text();
        }
        error_ = new std::string(status.Text());
        error_code_ = RegexpErrorToRE2(status.code());
        error_arg_ = new std::string(status.error_arg());
        return;
    }

    bool foldcase;
    re2::Regexp *suffix;
    if (entire_regexp_->RequiredPrefix(&prefix_, &foldcase, &suffix)) {
        prefix_foldcase_ = foldcase;
        suffix_regexp_ = suffix;
    } else {
        suffix_regexp_ = entire_regexp_->Incref();
    }

    // Two thirds of the memory goes to the forward Prog,
    // one third to the reverse prog, because the forward
    // Prog has two DFAs but the reverse prog has one.
    prog_ = suffix_regexp_->CompileToProg(options_.max_mem() * 2 / 3);
    if (prog_ == NULL) {
        if (options_.log_errors())
            LOG(ERROR) << "Error compiling '" << trunc(*pattern_) << "'";
        error_ = new std::string("pattern too large - compile failed");
        error_code_ = RE2::ErrorPatternTooLarge;
        return;
    }

    // We used to compute this lazily, but it's used during the
    // typical control flow for a match call, so we now compute
    // it eagerly, which avoids the overhead of std::once_flag.
    num_captures_ = suffix_regexp_->NumCaptures();

    // Could delay this until the first match call that
    // cares about submatch information, but the one-pass
    // machine's memory gets cut from the DFA memory budget,
    // and that is harder to do if the DFA has already
    // been built.
    is_one_pass_ = prog_->IsOnePass();
}

// Returns rprog_, computing it if needed.
re2::Prog *RE2::ReverseProg() const {
    std::call_once(
        rprog_once_,
        [](const RE2 *re) {
            re->rprog_ = re->suffix_regexp_->CompileToReverseProg(re->options_.max_mem() / 3);
            if (re->rprog_ == NULL) {
                if (re->options_.log_errors())
                    LOG(ERROR) << "Error reverse compiling '" << trunc(*re->pattern_) << "'";
                // We no longer touch error_ and error_code_ because failing to compile
                // the reverse Prog is not a showstopper: falling back to NFA execution
                // is fine. More importantly, an RE2 object is supposed to be logically
                // immutable: whatever ok() would have returned after Init() completed,
                // it should continue to return that no matter what ReverseProg() does.
            }
        },
        this);
    return rprog_;
}

RE2::~RE2() {
    if (group_names_ != empty_group_names())
        delete group_names_;
    if (named_groups_ != empty_named_groups())
        delete named_groups_;
    delete rprog_;
    delete prog_;
    if (error_arg_ != empty_string())
        delete error_arg_;
    if (error_ != empty_string())
        delete error_;
    if (suffix_regexp_)
        suffix_regexp_->Decref();
    if (entire_regexp_)
        entire_regexp_->Decref();
    delete pattern_;
}

int RE2::ProgramSize() const {
    if (prog_ == NULL)
        return -1;
    return prog_->size();
}

int RE2::ReverseProgramSize() const {
    if (prog_ == NULL)
        return -1;
    Prog *prog = ReverseProg();
    if (prog == NULL)
        return -1;
    return prog->size();
}

// Finds the most significant non-zero bit in n.
static int FindMSBSet(uint32_t n) {
    DCHECK_NE(n, 0);
#if defined(__GNUC__)
    return 31 ^ __builtin_clz(n);
#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_IX86))
    unsigned long c;
    _BitScanReverse(&c, n);
    return static_cast<int>(c);
#else
    int c = 0;
    for (int shift = 1 << 4; shift != 0; shift >>= 1) {
        uint32_t word = n >> shift;
        if (word != 0) {
            n = word;
            c += shift;
        }
    }
    return c;
#endif
}

static int Fanout(Prog *prog, std::vector<int> *histogram) {
    SparseArray<int> fanout(prog->size());
    prog->Fanout(&fanout);
    int data[32] = {};
    int size = 0;
    for (SparseArray<int>::iterator i = fanout.begin(); i != fanout.end(); ++i) {
        if (i->value() == 0)
            continue;
        uint32_t value = i->value();
        int bucket = FindMSBSet(value);
        bucket += value & (value - 1) ? 1 : 0;
        ++data[bucket];
        size = std::max(size, bucket + 1);
    }
    if (histogram != NULL)
        histogram->assign(data, data + size);
    return size - 1;
}

int RE2::ProgramFanout(std::vector<int> *histogram) const {
    if (prog_ == NULL)
        return -1;
    return Fanout(prog_, histogram);
}

int RE2::ReverseProgramFanout(std::vector<int> *histogram) const {
    if (prog_ == NULL)
        return -1;
    Prog *prog = ReverseProg();
    if (prog == NULL)
        return -1;
    return Fanout(prog, histogram);
}

// Returns named_groups_, computing it if needed.
const std::map<std::string, int> &RE2::NamedCapturingGroups() const {
    std::call_once(
        named_groups_once_,
        [](const RE2 *re) {
            if (re->suffix_regexp_ != NULL)
                re->named_groups_ = re->suffix_regexp_->NamedCaptures();
            if (re->named_groups_ == NULL)
                re->named_groups_ = empty_named_groups();
        },
        this);
    return *named_groups_;
}

// Returns group_names_, computing it if needed.
const std::map<int, std::string> &RE2::CapturingGroupNames() const {
    std::call_once(
        group_names_once_,
        [](const RE2 *re) {
            if (re->suffix_regexp_ != NULL)
                re->group_names_ = re->suffix_regexp_->CaptureNames();
            if (re->group_names_ == NULL)
                re->group_names_ = empty_group_names();
        },
        this);
    return *group_names_;
}

/***** Convenience interfaces *****/

bool RE2::FullMatchN(const StringPiece &text, const RE2 &re, const Arg *const args[], int n) { return re.DoMatch(text, ANCHOR_BOTH, NULL, args, n); }

bool RE2::PartialMatchN(const StringPiece &text, const RE2 &re, const Arg *const args[], int n) {
    return re.DoMatch(text, UNANCHORED, NULL, args, n);
}

bool RE2::ConsumeN(StringPiece *input, const RE2 &re, const Arg *const args[], int n) {
    size_t consumed;
    if (re.DoMatch(*input, ANCHOR_START, &consumed, args, n)) {
        input->remove_prefix(consumed);
        return true;
    } else {
        return false;
    }
}

bool RE2::FindAndConsumeN(StringPiece *input, const RE2 &re, const Arg *const args[], int n) {
    size_t consumed;
    if (re.DoMatch(*input, UNANCHORED, &consumed, args, n)) {
        input->remove_prefix(consumed);
        return true;
    } else {
        return false;
    }
}

bool RE2::Replace(std::string *str, const RE2 &re, const StringPiece &rewrite) {
    StringPiece vec[kVecSize];
    int nvec = 1 + MaxSubmatch(rewrite);
    if (nvec > 1 + re.NumberOfCapturingGroups())
        return false;
    if (nvec > static_cast<int>(arraysize(vec)))
        return false;
    if (!re.Match(*str, 0, str->size(), UNANCHORED, vec, nvec))
        return false;

    std::string s;
    if (!re.Rewrite(&s, rewrite, vec, nvec))
        return false;

    assert(vec[0].data() >= str->data());
    assert(vec[0].data() + vec[0].size() <= str->data() + str->size());
    str->replace(vec[0].data() - str->data(), vec[0].size(), s);
    return true;
}

int RE2::GlobalReplace(std::string *str, const RE2 &re, const StringPiece &rewrite) {
    StringPiece vec[kVecSize];
    int nvec = 1 + MaxSubmatch(rewrite);
    if (nvec > 1 + re.NumberOfCapturingGroups())
        return false;
    if (nvec > static_cast<int>(arraysize(vec)))
        return false;

    const char *p = str->data();
    const char *ep = p + str->size();
    const char *lastend = NULL;
    std::string out;
    int count = 0;
    while (p <= ep) {
        if (maximum_global_replace_count != -1 && count >= maximum_global_replace_count)
            break;
        if (!re.Match(*str, static_cast<size_t>(p - str->data()), str->size(), UNANCHORED, vec, nvec))
            break;
        if (p < vec[0].data())
            out.append(p, vec[0].data() - p);
        if (vec[0].data() == lastend && vec[0].empty()) {
            // Disallow empty match at end of last match: skip ahead.
            //
            // fullrune() takes int, not ptrdiff_t. However, it just looks
            // at the leading byte and treats any length >= 4 the same.
            if (re.options().encoding() == RE2::Options::EncodingUTF8 && fullrune(p, static_cast<int>(std::min(ptrdiff_t{4}, ep - p)))) {
                // re is in UTF-8 mode and there is enough left of str
                // to allow us to advance by up to UTFmax bytes.
                Rune r;
                int n = chartorune(&r, p);
                // Some copies of chartorune have a bug that accepts
                // encodings of values in (10FFFF, 1FFFFF] as valid.
                if (r > Runemax) {
                    n = 1;
                    r = Runeerror;
                }
                if (!(n == 1 && r == Runeerror)) { // no decoding error
                    out.append(p, n);
                    p += n;
                    continue;
                }
            }
            // Most likely, re is in Latin-1 mode. If it is in UTF-8 mode,
            // we fell through from above and the GIGO principle applies.
            if (p < ep)
                out.append(p, 1);
            p++;
            continue;
        }
        re.Rewrite(&out, rewrite, vec, nvec);
        p = vec[0].data() + vec[0].size();
        lastend = p;
        count++;
    }

    if (count == 0)
        return 0;

    if (p < ep)
        out.append(p, ep - p);
    using std::swap;
    swap(out, *str);
    return count;
}

bool RE2::Extract(const StringPiece &text, const RE2 &re, const StringPiece &rewrite, std::string *out) {
    StringPiece vec[kVecSize];
    int nvec = 1 + MaxSubmatch(rewrite);
    if (nvec > 1 + re.NumberOfCapturingGroups())
        return false;
    if (nvec > static_cast<int>(arraysize(vec)))
        return false;
    if (!re.Match(text, 0, text.size(), UNANCHORED, vec, nvec))
        return false;

    out->clear();
    return re.Rewrite(out, rewrite, vec, nvec);
}

std::string RE2::QuoteMeta(const StringPiece &unquoted) {
    std::string result;
    result.reserve(unquoted.size() << 1);

    // Escape any ascii character not in [A-Za-z_0-9].
    //
    // Note that it's legal to escape a character even if it has no
    // special meaning in a regular expression -- so this function does
    // that.  (This also makes it identical to the perl function of the
    // same name except for the null-character special case;
    // see `perldoc -f quotemeta`.)
    for (size_t ii = 0; ii < unquoted.size(); ++ii) {
        // Note that using 'isalnum' here raises the benchmark time from
        // 32ns to 58ns:
        if ((unquoted[ii] < 'a' || unquoted[ii] > 'z') && (unquoted[ii] < 'A' || unquoted[ii] > 'Z') && (unquoted[ii] < '0' || unquoted[ii] > '9') &&
            unquoted[ii] != '_' &&
            // If this is the part of a UTF8 or Latin1 character, we need
            // to copy this byte without escaping.  Experimentally this is
            // what works correctly with the regexp library.
            !(unquoted[ii] & 128)) {
            if (unquoted[ii] == '\0') { // Special handling for null chars.
                // Note that this special handling is not strictly required for RE2,
                // but this quoting is required for other regexp libraries such as
                // PCRE.
                // Can't use "\\0" since the next character might be a digit.
                result += "\\x00";
                continue;
            }
            result += '\\';
        }
        result += unquoted[ii];
    }

    return result;
}

bool RE2::PossibleMatchRange(std::string *min, std::string *max, int maxlen) const {
    if (prog_ == NULL)
        return false;

    int n = static_cast<int>(prefix_.size());
    if (n > maxlen)
        n = maxlen;

    // Determine initial min max from prefix_ literal.
    *min = prefix_.substr(0, n);
    *max = prefix_.substr(0, n);
    if (prefix_foldcase_) {
        // prefix is ASCII lowercase; change *min to uppercase.
        for (int i = 0; i < n; i++) {
            char &c = (*min)[i];
            if ('a' <= c && c <= 'z')
                c += 'A' - 'a';
        }
    }

    // Add to prefix min max using PossibleMatchRange on regexp.
    std::string dmin, dmax;
    maxlen -= n;
    if (maxlen > 0 && prog_->PossibleMatchRange(&dmin, &dmax, maxlen)) {
        min->append(dmin);
        max->append(dmax);
    } else if (!max->empty()) {
        // prog_->PossibleMatchRange has failed us,
        // but we still have useful information from prefix_.
        // Round up *max to allow any possible suffix.
        PrefixSuccessor(max);
    } else {
        // Nothing useful.
        *min = "";
        *max = "";
        return false;
    }

    return true;
}

// Avoid possible locale nonsense in standard strcasecmp.
// The string a is known to be all lowercase.
static int ascii_strcasecmp(const char *a, const char *b, size_t len) {
    const char *ae = a + len;

    for (; a < ae; a++, b++) {
        uint8_t x = *a;
        uint8_t y = *b;
        if ('A' <= y && y <= 'Z')
            y += 'a' - 'A';
        if (x != y)
            return x - y;
    }
    return 0;
}

/***** Actual matching and rewriting code *****/

bool RE2::Match(const StringPiece &text, size_t startpos, size_t endpos, Anchor re_anchor, StringPiece *submatch, int nsubmatch) const {
    if (!ok()) {
        if (options_.log_errors())
            LOG(ERROR) << "Invalid RE2: " << *error_;
        return false;
    }

    if (startpos > endpos || endpos > text.size()) {
        if (options_.log_errors())
            LOG(ERROR) << "RE2: invalid startpos, endpos pair. ["
                       << "startpos: " << startpos << ", "
                       << "endpos: " << endpos << ", "
                       << "text size: " << text.size() << "]";
        return false;
    }

    StringPiece subtext = text;
    subtext.remove_prefix(startpos);
    subtext.remove_suffix(text.size() - endpos);

    // Use DFAs to find exact location of match, filter out non-matches.

    // Don't ask for the location if we won't use it.
    // SearchDFA can do extra optimizations in that case.
    StringPiece match;
    StringPiece *matchp = &match;
    if (nsubmatch == 0)
        matchp = NULL;

    int ncap = 1 + NumberOfCapturingGroups();
    if (ncap > nsubmatch)
        ncap = nsubmatch;

    // If the regexp is anchored explicitly, must not be in middle of text.
    if (prog_->anchor_start() && startpos != 0)
        return false;
    if (prog_->anchor_end() && endpos != text.size())
        return false;

    // If the regexp is anchored explicitly, update re_anchor
    // so that we can potentially fall into a faster case below.
    if (prog_->anchor_start() && prog_->anchor_end())
        re_anchor = ANCHOR_BOTH;
    else if (prog_->anchor_start() && re_anchor != ANCHOR_BOTH)
        re_anchor = ANCHOR_START;

    // Check for the required prefix, if any.
    size_t prefixlen = 0;
    if (!prefix_.empty()) {
        if (startpos != 0)
            return false;
        prefixlen = prefix_.size();
        if (prefixlen > subtext.size())
            return false;
        if (prefix_foldcase_) {
            if (ascii_strcasecmp(&prefix_[0], subtext.data(), prefixlen) != 0)
                return false;
        } else {
            if (memcmp(&prefix_[0], subtext.data(), prefixlen) != 0)
                return false;
        }
        subtext.remove_prefix(prefixlen);
        // If there is a required prefix, the anchor must be at least ANCHOR_START.
        if (re_anchor != ANCHOR_BOTH)
            re_anchor = ANCHOR_START;
    }

    Prog::Anchor anchor = Prog::kUnanchored;
    Prog::MatchKind kind = longest_match_ ? Prog::kLongestMatch : Prog::kFirstMatch;

    bool can_one_pass = is_one_pass_ && ncap <= Prog::kMaxOnePassCapture;
    bool can_bit_state = prog_->CanBitState();
    size_t bit_state_text_max_size = prog_->bit_state_text_max_size();

#ifdef RE2_HAVE_THREAD_LOCAL
    hooks::context = this;
#endif
    bool dfa_failed = false;
    bool skipped_test = false;
    switch (re_anchor) {
        default:
            LOG(DFATAL) << "Unexpected re_anchor value: " << re_anchor;
            return false;

        case UNANCHORED: {
            if (prog_->anchor_end()) {
                // This is a very special case: we don't need the forward DFA because
                // we already know where the match must end! Instead, the reverse DFA
                // can say whether there is a match and (optionally) where it starts.
                Prog *prog = ReverseProg();
                if (prog == NULL) {
                    // Fall back to NFA below.
                    skipped_test = true;
                    break;
                }
                if (!prog->SearchDFA(subtext, text, Prog::kAnchored, Prog::kLongestMatch, matchp, &dfa_failed, NULL)) {
                    if (dfa_failed) {
                        if (options_.log_errors())
                            LOG(ERROR) << "DFA out of memory: "
                                       << "pattern length " << pattern_->size() << ", "
                                       << "program size " << prog->size() << ", "
                                       << "list count " << prog->list_count() << ", "
                                       << "bytemap range " << prog->bytemap_range();
                        // Fall back to NFA below.
                        skipped_test = true;
                        break;
                    }
                    return false;
                }
                if (matchp == NULL) // Matched.  Don't care where.
                    return true;
                break;
            }

            if (!prog_->SearchDFA(subtext, text, anchor, kind, matchp, &dfa_failed, NULL)) {
                if (dfa_failed) {
                    if (options_.log_errors())
                        LOG(ERROR) << "DFA out of memory: "
                                   << "pattern length " << pattern_->size() << ", "
                                   << "program size " << prog_->size() << ", "
                                   << "list count " << prog_->list_count() << ", "
                                   << "bytemap range " << prog_->bytemap_range();
                    // Fall back to NFA below.
                    skipped_test = true;
                    break;
                }
                return false;
            }
            if (matchp == NULL) // Matched.  Don't care where.
                return true;
            // SearchDFA set match.end() but didn't know where the
            // match started.  Run the regexp backward from match.end()
            // to find the longest possible match -- that's where it started.
            Prog *prog = ReverseProg();
            if (prog == NULL) {
                // Fall back to NFA below.
                skipped_test = true;
                break;
            }
            if (!prog->SearchDFA(match, text, Prog::kAnchored, Prog::kLongestMatch, &match, &dfa_failed, NULL)) {
                if (dfa_failed) {
                    if (options_.log_errors())
                        LOG(ERROR) << "DFA out of memory: "
                                   << "pattern length " << pattern_->size() << ", "
                                   << "program size " << prog->size() << ", "
                                   << "list count " << prog->list_count() << ", "
                                   << "bytemap range " << prog->bytemap_range();
                    // Fall back to NFA below.
                    skipped_test = true;
                    break;
                }
                if (options_.log_errors())
                    LOG(ERROR) << "SearchDFA inconsistency";
                return false;
            }
            break;
        }

        case ANCHOR_BOTH:
        case ANCHOR_START:
            if (re_anchor == ANCHOR_BOTH)
                kind = Prog::kFullMatch;
            anchor = Prog::kAnchored;

            // If only a small amount of text and need submatch
            // information anyway and we're going to use OnePass or BitState
            // to get it, we might as well not even bother with the DFA:
            // OnePass or BitState will be fast enough.
            // On tiny texts, OnePass outruns even the DFA, and
            // it doesn't have the shared state and occasional mutex that
            // the DFA does.
            if (can_one_pass && text.size() <= 4096 && (ncap > 1 || text.size() <= 16)) {
                skipped_test = true;
                break;
            }
            if (can_bit_state && text.size() <= bit_state_text_max_size && ncap > 1) {
                skipped_test = true;
                break;
            }
            if (!prog_->SearchDFA(subtext, text, anchor, kind, &match, &dfa_failed, NULL)) {
                if (dfa_failed) {
                    if (options_.log_errors())
                        LOG(ERROR) << "DFA out of memory: "
                                   << "pattern length " << pattern_->size() << ", "
                                   << "program size " << prog_->size() << ", "
                                   << "list count " << prog_->list_count() << ", "
                                   << "bytemap range " << prog_->bytemap_range();
                    // Fall back to NFA below.
                    skipped_test = true;
                    break;
                }
                return false;
            }
            break;
    }

    if (!skipped_test && ncap <= 1) {
        // We know exactly where it matches.  That's enough.
        if (ncap == 1)
            submatch[0] = match;
    } else {
        StringPiece subtext1;
        if (skipped_test) {
            // DFA ran out of memory or was skipped:
            // need to search in entire original text.
            subtext1 = subtext;
        } else {
            // DFA found the exact match location:
            // let NFA run an anchored, full match search
            // to find submatch locations.
            subtext1 = match;
            anchor = Prog::kAnchored;
            kind = Prog::kFullMatch;
        }

        if (can_one_pass && anchor != Prog::kUnanchored) {
            if (!prog_->SearchOnePass(subtext1, text, anchor, kind, submatch, ncap)) {
                if (!skipped_test && options_.log_errors())
                    LOG(ERROR) << "SearchOnePass inconsistency";
                return false;
            }
        } else if (can_bit_state && subtext1.size() <= bit_state_text_max_size) {
            if (!prog_->SearchBitState(subtext1, text, anchor, kind, submatch, ncap)) {
                if (!skipped_test && options_.log_errors())
                    LOG(ERROR) << "SearchBitState inconsistency";
                return false;
            }
        } else {
            if (!prog_->SearchNFA(subtext1, text, anchor, kind, submatch, ncap)) {
                if (!skipped_test && options_.log_errors())
                    LOG(ERROR) << "SearchNFA inconsistency";
                return false;
            }
        }
    }

    // Adjust overall match for required prefix that we stripped off.
    if (prefixlen > 0 && nsubmatch > 0)
        submatch[0] = StringPiece(submatch[0].data() - prefixlen, submatch[0].size() + prefixlen);

    // Zero submatches that don't exist in the regexp.
    for (int i = ncap; i < nsubmatch; i++)
        submatch[i] = StringPiece();
    return true;
}

// Internal matcher - like Match() but takes Args not StringPieces.
bool RE2::DoMatch(const StringPiece &text, Anchor re_anchor, size_t *consumed, const Arg *const *args, int n) const {
    if (!ok()) {
        if (options_.log_errors())
            LOG(ERROR) << "Invalid RE2: " << *error_;
        return false;
    }

    if (NumberOfCapturingGroups() < n) {
        // RE has fewer capturing groups than number of Arg pointers passed in.
        return false;
    }

    // Count number of capture groups needed.
    int nvec;
    if (n == 0 && consumed == NULL)
        nvec = 0;
    else
        nvec = n + 1;

    StringPiece *vec;
    StringPiece stkvec[kVecSize];
    StringPiece *heapvec = NULL;

    if (nvec <= static_cast<int>(arraysize(stkvec))) {
        vec = stkvec;
    } else {
        vec = new StringPiece[nvec];
        heapvec = vec;
    }

    if (!Match(text, 0, text.size(), re_anchor, vec, nvec)) {
        delete[] heapvec;
        return false;
    }

    if (consumed != NULL)
        *consumed = static_cast<size_t>(EndPtr(vec[0]) - BeginPtr(text));

    if (n == 0 || args == NULL) {
        // We are not interested in results
        delete[] heapvec;
        return true;
    }

    // If we got here, we must have matched the whole pattern.
    for (int i = 0; i < n; i++) {
        const StringPiece &s = vec[i + 1];
        if (!args[i]->Parse(s.data(), s.size())) {
            // TODO: Should we indicate what the error was?
            delete[] heapvec;
            return false;
        }
    }

    delete[] heapvec;
    return true;
}

// Checks that the rewrite string is well-formed with respect to this
// regular expression.
bool RE2::CheckRewriteString(const StringPiece &rewrite, std::string *error) const {
    int max_token = -1;
    for (const char *s = rewrite.data(), *end = s + rewrite.size(); s < end; s++) {
        int c = *s;
        if (c != '\\') {
            continue;
        }
        if (++s == end) {
            *error = "Rewrite schema error: '\\' not allowed at end.";
            return false;
        }
        c = *s;
        if (c == '\\') {
            continue;
        }
        if (!isdigit(c)) {
            *error = "Rewrite schema error: "
                     "'\\' must be followed by a digit or '\\'.";
            return false;
        }
        int n = (c - '0');
        if (max_token < n) {
            max_token = n;
        }
    }

    if (max_token > NumberOfCapturingGroups()) {
        *error = StringPrintf("Rewrite schema requests %d matches, but the regexp only has %d "
                              "parenthesized subexpressions.",
                              max_token,
                              NumberOfCapturingGroups());
        return false;
    }
    return true;
}

// Returns the maximum submatch needed for the rewrite to be done by Replace().
// E.g. if rewrite == "foo \\2,\\1", returns 2.
int RE2::MaxSubmatch(const StringPiece &rewrite) {
    int max = 0;
    for (const char *s = rewrite.data(), *end = s + rewrite.size(); s < end; s++) {
        if (*s == '\\') {
            s++;
            int c = (s < end) ? *s : -1;
            if (isdigit(c)) {
                int n = (c - '0');
                if (n > max)
                    max = n;
            }
        }
    }
    return max;
}

// Append the "rewrite" string, with backslash subsitutions from "vec",
// to string "out".
bool RE2::Rewrite(std::string *out, const StringPiece &rewrite, const StringPiece *vec, int veclen) const {
    for (const char *s = rewrite.data(), *end = s + rewrite.size(); s < end; s++) {
        if (*s != '\\') {
            out->push_back(*s);
            continue;
        }
        s++;
        int c = (s < end) ? *s : -1;
        if (isdigit(c)) {
            int n = (c - '0');
            if (n >= veclen) {
                if (options_.log_errors()) {
                    LOG(ERROR) << "invalid substitution \\" << n << " from " << veclen << " groups";
                }
                return false;
            }
            StringPiece snip = vec[n];
            if (!snip.empty())
                out->append(snip.data(), snip.size());
        } else if (c == '\\') {
            out->push_back('\\');
        } else {
            if (options_.log_errors())
                LOG(ERROR) << "invalid rewrite pattern: " << rewrite.data();
            return false;
        }
    }
    return true;
}

/***** Parsers for various types *****/

namespace re2_internal {

template <>
bool Parse(const char *str, size_t n, void *dest) {
    // We fail if somebody asked us to store into a non-NULL void* pointer
    return (dest == NULL);
}

template <>
bool Parse(const char *str, size_t n, std::string *dest) {
    if (dest == NULL)
        return true;
    dest->assign(str, n);
    return true;
}

template <>
bool Parse(const char *str, size_t n, StringPiece *dest) {
    if (dest == NULL)
        return true;
    *dest = StringPiece(str, n);
    return true;
}

template <>
bool Parse(const char *str, size_t n, char *dest) {
    if (n != 1)
        return false;
    if (dest == NULL)
        return true;
    *dest = str[0];
    return true;
}

template <>
bool Parse(const char *str, size_t n, signed char *dest) {
    if (n != 1)
        return false;
    if (dest == NULL)
        return true;
    *dest = str[0];
    return true;
}

template <>
bool Parse(const char *str, size_t n, unsigned char *dest) {
    if (n != 1)
        return false;
    if (dest == NULL)
        return true;
    *dest = str[0];
    return true;
}

// Largest number spec that we are willing to parse
static const int kMaxNumberLength = 32;

// REQUIRES "buf" must have length at least nbuf.
// Copies "str" into "buf" and null-terminates.
// Overwrites *np with the new length.
static const char *TerminateNumber(char *buf, size_t nbuf, const char *str, size_t *np, bool accept_spaces) {
    size_t n = *np;
    if (n == 0)
        return "";
    if (n > 0 && isspace(*str)) {
        // We are less forgiving than the strtoxxx() routines and do not
        // allow leading spaces. We do allow leading spaces for floats.
        if (!accept_spaces) {
            return "";
        }
        while (n > 0 && isspace(*str)) {
            n--;
            str++;
        }
    }

    // Although buf has a fixed maximum size, we can still handle
    // arbitrarily large integers correctly by omitting leading zeros.
    // (Numbers that are still too long will be out of range.)
    // Before deciding whether str is too long,
    // remove leading zeros with s/000+/00/.
    // Leaving the leading two zeros in place means that
    // we don't change 0000x123 (invalid) into 0x123 (valid).
    // Skip over leading - before replacing.
    bool neg = false;
    if (n >= 1 && str[0] == '-') {
        neg = true;
        n--;
        str++;
    }

    if (n >= 3 && str[0] == '0' && str[1] == '0') {
        while (n >= 3 && str[2] == '0') {
            n--;
            str++;
        }
    }

    if (neg) { // make room in buf for -
        n++;
        str--;
    }

    if (n > nbuf - 1)
        return "";

    memmove(buf, str, n);
    if (neg) {
        buf[0] = '-';
    }
    buf[n] = '\0';
    *np = n;
    return buf;
}

template <>
bool Parse(const char *str, size_t n, float *dest) {
    if (n == 0)
        return false;
    static const int kMaxLength = 200;
    char buf[kMaxLength + 1];
    str = TerminateNumber(buf, sizeof buf, str, &n, true);
    char *end;
    errno = 0;
    float r = strtof(str, &end);
    if (end != str + n)
        return false; // Leftover junk
    if (errno)
        return false;
    if (dest == NULL)
        return true;
    *dest = r;
    return true;
}

template <>
bool Parse(const char *str, size_t n, double *dest) {
    if (n == 0)
        return false;
    static const int kMaxLength = 200;
    char buf[kMaxLength + 1];
    str = TerminateNumber(buf, sizeof buf, str, &n, true);
    char *end;
    errno = 0;
    double r = strtod(str, &end);
    if (end != str + n)
        return false; // Leftover junk
    if (errno)
        return false;
    if (dest == NULL)
        return true;
    *dest = r;
    return true;
}

template <>
bool Parse(const char *str, size_t n, long *dest, int radix) {
    if (n == 0)
        return false;
    char buf[kMaxNumberLength + 1];
    str = TerminateNumber(buf, sizeof buf, str, &n, false);
    char *end;
    errno = 0;
    long r = strtol(str, &end, radix);
    if (end != str + n)
        return false; // Leftover junk
    if (errno)
        return false;
    if (dest == NULL)
        return true;
    *dest = r;
    return true;
}

template <>
bool Parse(const char *str, size_t n, unsigned long *dest, int radix) {
    if (n == 0)
        return false;
    char buf[kMaxNumberLength + 1];
    str = TerminateNumber(buf, sizeof buf, str, &n, false);
    if (str[0] == '-') {
        // strtoul() will silently accept negative numbers and parse
        // them.  This module is more strict and treats them as errors.
        return false;
    }

    char *end;
    errno = 0;
    unsigned long r = strtoul(str, &end, radix);
    if (end != str + n)
        return false; // Leftover junk
    if (errno)
        return false;
    if (dest == NULL)
        return true;
    *dest = r;
    return true;
}

template <>
bool Parse(const char *str, size_t n, short *dest, int radix) {
    long r;
    if (!Parse(str, n, &r, radix))
        return false; // Could not parse
    if ((short)r != r)
        return false; // Out of range
    if (dest == NULL)
        return true;
    *dest = (short)r;
    return true;
}

template <>
bool Parse(const char *str, size_t n, unsigned short *dest, int radix) {
    unsigned long r;
    if (!Parse(str, n, &r, radix))
        return false; // Could not parse
    if ((unsigned short)r != r)
        return false; // Out of range
    if (dest == NULL)
        return true;
    *dest = (unsigned short)r;
    return true;
}

template <>
bool Parse(const char *str, size_t n, int *dest, int radix) {
    long r;
    if (!Parse(str, n, &r, radix))
        return false; // Could not parse
    if ((int)r != r)
        return false; // Out of range
    if (dest == NULL)
        return true;
    *dest = (int)r;
    return true;
}

template <>
bool Parse(const char *str, size_t n, unsigned int *dest, int radix) {
    unsigned long r;
    if (!Parse(str, n, &r, radix))
        return false; // Could not parse
    if ((unsigned int)r != r)
        return false; // Out of range
    if (dest == NULL)
        return true;
    *dest = (unsigned int)r;
    return true;
}

template <>
bool Parse(const char *str, size_t n, long long *dest, int radix) {
    if (n == 0)
        return false;
    char buf[kMaxNumberLength + 1];
    str = TerminateNumber(buf, sizeof buf, str, &n, false);
    char *end;
    errno = 0;
    long long r = strtoll(str, &end, radix);
    if (end != str + n)
        return false; // Leftover junk
    if (errno)
        return false;
    if (dest == NULL)
        return true;
    *dest = r;
    return true;
}

template <>
bool Parse(const char *str, size_t n, unsigned long long *dest, int radix) {
    if (n == 0)
        return false;
    char buf[kMaxNumberLength + 1];
    str = TerminateNumber(buf, sizeof buf, str, &n, false);
    if (str[0] == '-') {
        // strtoull() will silently accept negative numbers and parse
        // them.  This module is more strict and treats them as errors.
        return false;
    }
    char *end;
    errno = 0;
    unsigned long long r = strtoull(str, &end, radix);
    if (end != str + n)
        return false; // Leftover junk
    if (errno)
        return false;
    if (dest == NULL)
        return true;
    *dest = r;
    return true;
}

} // namespace re2_internal

namespace hooks {

#ifdef RE2_HAVE_THREAD_LOCAL
thread_local const RE2 *context = NULL;
#endif

template <typename T>
union Hook {
    void Store(T *cb) { cb_.store(cb, std::memory_order_release); }
    T *Load() const { return cb_.load(std::memory_order_acquire); }

#if !defined(__clang__) && defined(_MSC_VER)
    // Citing https://github.com/protocolbuffers/protobuf/pull/4777 as precedent,
    // this is a gross hack to make std::atomic<T*> constant-initialized on MSVC.
    static_assert(ATOMIC_POINTER_LOCK_FREE == 2, "std::atomic<T*> must be always lock-free");
    T *cb_for_constinit_;
#endif

    std::atomic<T *> cb_;
};

template <typename T>
static void DoNothing(const T &) {}

#define DEFINE_HOOK(type, name)                                                                                                                      \
    static Hook<type##Callback> name##_hook = {{&DoNothing<type>}};                                                                                  \
    void Set##type##Hook(type##Callback *cb) { name##_hook.Store(cb); }                                                                              \
    type##Callback *Get##type##Hook() { return name##_hook.Load(); }

DEFINE_HOOK(DFAStateCacheReset, dfa_state_cache_reset)
DEFINE_HOOK(DFASearchFailure, dfa_search_failure)

#undef DEFINE_HOOK

} // namespace hooks

} // namespace re2