text: //===-- Regex.cpp - Regular Expression matcher implementation -------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file implements a POSIX regular expression matcher.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/Support/Regex.h"
  #include "llvm/Support/ErrorHandling.h"
  #include "llvm/Support/raw_ostream.h"
  #include "llvm/ADT/SmallVector.h"
  #include "regex_impl.h"
  #include <string>
  using namespace llvm;
  
  Regex::Regex(StringRef regex, unsigned Flags) {
    unsigned flags = 0;
    preg = new llvm_regex();
    preg->re_endp = regex.end();
    if (Flags & IgnoreCase) 
      flags |= REG_ICASE;
    if (Flags & Newline)
      flags |= REG_NEWLINE;
    error = llvm_regcomp(preg, regex.data(), flags|REG_EXTENDED|REG_PEND);
  }
  
  Regex::~Regex() {
    llvm_regfree(preg);
    delete preg;
  }
  
  bool Regex::isValid(std::string &Error) {
    if (!error)
      return true;
    
    size_t len = llvm_regerror(error, preg, NULL, 0);
    
    Error.resize(len);
    llvm_regerror(error, preg, &Error[0], len);
    return false;
  }
  
  /// getNumMatches - In a valid regex, return the number of parenthesized
  /// matches it contains.
  unsigned Regex::getNumMatches() const {
    return preg->re_nsub;
  }
  
  bool Regex::match(StringRef String, SmallVectorImpl<StringRef> *Matches){
    unsigned nmatch = Matches ? preg->re_nsub+1 : 0;
  
    // pmatch needs to have at least one element.
    SmallVector<llvm_regmatch_t, 8> pm;
    pm.resize(nmatch > 0 ? nmatch : 1);
    pm[0].rm_so = 0;
    pm[0].rm_eo = String.size();
  
    int rc = llvm_regexec(preg, String.data(), nmatch, pm.data(), REG_STARTEND);
  
    if (rc == REG_NOMATCH)
      return false;
    if (rc != 0) {
      // regexec can fail due to invalid pattern or running out of memory.
      error = rc;
      return false;
    }
  
    // There was a match.
  
    if (Matches) { // match position requested
      Matches->clear();
      
      for (unsigned i = 0; i != nmatch; ++i) {
        if (pm[i].rm_so == -1) {
          // this group didn't match
          Matches->push_back(StringRef());
          continue;
        }
        assert(pm[i].rm_eo >= pm[i].rm_so);
        Matches->push_back(StringRef(String.data()+pm[i].rm_so,
                                     pm[i].rm_eo-pm[i].rm_so));
      }
    }
  
    return true;
  }
  
  std::string Regex::sub(StringRef Repl, StringRef String,
                         std::string *Error) {
    SmallVector<StringRef, 8> Matches;
  
    // Reset error, if given.
    if (Error && !Error->empty()) *Error = "";
  
    // Return the input if there was no match.
    if (!match(String, &Matches))
      return String;
  
    // Otherwise splice in the replacement string, starting with the prefix before
    // the match.
    std::string Res(String.begin(), Matches[0].begin());
  
    // Then the replacement string, honoring possible substitutions.
    while (!Repl.empty()) {
      // Skip to the next escape.
      std::pair<StringRef, StringRef> Split = Repl.split('\\');
  
      // Add the skipped substring.
      Res += Split.first;
  
      // Check for terminimation and trailing backslash.
      if (Split.second.empty()) {
        if (Repl.size() != Split.first.size() &&
            Error && Error->empty())
          *Error = "replacement string contained trailing backslash";
        break;
      }
  
      // Otherwise update the replacement string and interpret escapes.
      Repl = Split.second;
  
      // FIXME: We should have a StringExtras function for mapping C99 escapes.
      switch (Repl[0]) {
        // Treat all unrecognized characters as self-quoting.
      default:
        Res += Repl[0];
        Repl = Repl.substr(1);
        break;
  
        // Single character escapes.
      case 't':
        Res += '\t';
        Repl = Repl.substr(1);
        break;
      case 'n':
        Res += '\n';
        Repl = Repl.substr(1);
        break;
  
        // Decimal escapes are backreferences.
      case '0': case '1': case '2': case '3': case '4':
      case '5': case '6': case '7': case '8': case '9': {
        // Extract the backreference number.
        StringRef Ref = Repl.slice(0, Repl.find_first_not_of("0123456789"));
        Repl = Repl.substr(Ref.size());
  
        unsigned RefValue;
        if (!Ref.getAsInteger(10, RefValue) &&
            RefValue < Matches.size())
          Res += Matches[RefValue];
        else if (Error && Error->empty())
          *Error = "invalid backreference string '" + Ref.str() + "'";
        break;
      }
      }
    }
  
    // And finally the suffix.
    Res += StringRef(Matches[0].end(), String.end() - Matches[0].end());
  
    return Res;
  }
  