text: //===-- StringRef.cpp - Lightweight String References ---------------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/ADT/StringRef.h"
  #include "llvm/ADT/APInt.h"
  #include "llvm/ADT/Hashing.h"
  #include "llvm/ADT/edit_distance.h"
  #include <bitset>
  
  using namespace llvm;
  
  // MSVC emits references to this into the translation units which reference it.
  #ifndef _MSC_VER
  const size_t StringRef::npos;
  #endif
  
  static char ascii_tolower(char x) {
    if (x >= 'A' && x <= 'Z')
      return x - 'A' + 'a';
    return x;
  }
  
  static char ascii_toupper(char x) {
    if (x >= 'a' && x <= 'z')
      return x - 'a' + 'A';
    return x;
  }
  
  static bool ascii_isdigit(char x) {
    return x >= '0' && x <= '9';
  }
  
  // strncasecmp() is not available on non-POSIX systems, so define an
  // alternative function here.
  static int ascii_strncasecmp(const char *LHS, const char *RHS, size_t Length) {
    for (size_t I = 0; I < Length; ++I) {
      unsigned char LHC = ascii_tolower(LHS[I]);
      unsigned char RHC = ascii_tolower(RHS[I]);
      if (LHC != RHC)
        return LHC < RHC ? -1 : 1;
    }
    return 0;
  }
  
  /// compare_lower - Compare strings, ignoring case.
  int StringRef::compare_lower(StringRef RHS) const {
    if (int Res = ascii_strncasecmp(Data, RHS.Data, std::min(Length, RHS.Length)))
      return Res;
    if (Length == RHS.Length)
      return 0;
    return Length < RHS.Length ? -1 : 1;
  }
  
  /// Check if this string starts with the given \p Prefix, ignoring case.
  bool StringRef::startswith_lower(StringRef Prefix) const {
    return Length >= Prefix.Length &&
        ascii_strncasecmp(Data, Prefix.Data, Prefix.Length) == 0;
  }
  
  /// Check if this string ends with the given \p Suffix, ignoring case.
  bool StringRef::endswith_lower(StringRef Suffix) const {
    return Length >= Suffix.Length &&
        ascii_strncasecmp(end() - Suffix.Length, Suffix.Data, Suffix.Length) == 0;
  }
  
  /// compare_numeric - Compare strings, handle embedded numbers.
  int StringRef::compare_numeric(StringRef RHS) const {
    for (size_t I = 0, E = std::min(Length, RHS.Length); I != E; ++I) {
      // Check for sequences of digits.
      if (ascii_isdigit(Data[I]) && ascii_isdigit(RHS.Data[I])) {
        // The longer sequence of numbers is considered larger.
        // This doesn't really handle prefixed zeros well.
        size_t J;
        for (J = I + 1; J != E + 1; ++J) {
          bool ld = J < Length && ascii_isdigit(Data[J]);
          bool rd = J < RHS.Length && ascii_isdigit(RHS.Data[J]);
          if (ld != rd)
            return rd ? -1 : 1;
          if (!rd)
            break;
        }
        // The two number sequences have the same length (J-I), just memcmp them.
        if (int Res = compareMemory(Data + I, RHS.Data + I, J - I))
          return Res < 0 ? -1 : 1;
        // Identical number sequences, continue search after the numbers.
        I = J - 1;
        continue;
      }
      if (Data[I] != RHS.Data[I])
        return (unsigned char)Data[I] < (unsigned char)RHS.Data[I] ? -1 : 1;
    }
    if (Length == RHS.Length)
      return 0;
    return Length < RHS.Length ? -1 : 1;
  }
  
  // Compute the edit distance between the two given strings.
  unsigned StringRef::edit_distance(llvm::StringRef Other,
                                    bool AllowReplacements,
                                    unsigned MaxEditDistance) const {
    return llvm::ComputeEditDistance(
        makeArrayRef(data(), size()),
        makeArrayRef(Other.data(), Other.size()),
        AllowReplacements, MaxEditDistance);
  }
  
  //===----------------------------------------------------------------------===//
  // String Operations
  //===----------------------------------------------------------------------===//
  
  std::string StringRef::lower() const {
    std::string Result(size(), char());
    for (size_type i = 0, e = size(); i != e; ++i) {
      Result[i] = ascii_tolower(Data[i]);
    }
    return Result;
  }
  
  std::string StringRef::upper() const {
    std::string Result(size(), char());
    for (size_type i = 0, e = size(); i != e; ++i) {
      Result[i] = ascii_toupper(Data[i]);
    }
    return Result;
  }
  
  //===----------------------------------------------------------------------===//
  // String Searching
  //===----------------------------------------------------------------------===//
  
  
  /// find - Search for the first string \arg Str in the string.
  ///
  /// \return - The index of the first occurrence of \arg Str, or npos if not
  /// found.
  size_t StringRef::find(StringRef Str, size_t From) const {
    size_t N = Str.size();
    if (N > Length)
      return npos;
  
    // For short haystacks or unsupported needles fall back to the naive algorithm
    if (Length < 16 || N > 255 || N == 0) {
      for (size_t e = Length - N + 1, i = std::min(From, e); i != e; ++i)
        if (substr(i, N).equals(Str))
          return i;
      return npos;
    }
  
    if (From >= Length)
      return npos;
  
    // Build the bad char heuristic table, with uint8_t to reduce cache thrashing.
    uint8_t BadCharSkip[256];
    std::memset(BadCharSkip, N, 256);
    for (unsigned i = 0; i != N-1; ++i)
      BadCharSkip[(uint8_t)Str[i]] = N-1-i;
  
    unsigned Len = Length-From, Pos = From;
    while (Len >= N) {
      if (substr(Pos, N).equals(Str)) // See if this is the correct substring.
        return Pos;
  
      // Otherwise skip the appropriate number of bytes.
      uint8_t Skip = BadCharSkip[(uint8_t)(*this)[Pos+N-1]];
      Len -= Skip;
      Pos += Skip;
    }
  
    return npos;
  }
  
  /// rfind - Search for the last string \arg Str in the string.
  ///
  /// \return - The index of the last occurrence of \arg Str, or npos if not
  /// found.
  size_t StringRef::rfind(StringRef Str) const {
    size_t N = Str.size();
    if (N > Length)
      return npos;
    for (size_t i = Length - N + 1, e = 0; i != e;) {
      --i;
      if (substr(i, N).equals(Str))
        return i;
    }
    return npos;
  }
  
  /// find_first_of - Find the first character in the string that is in \arg
  /// Chars, or npos if not found.
  ///
  /// Note: O(size() + Chars.size())
  StringRef::size_type StringRef::find_first_of(StringRef Chars,
                                                size_t From) const {
    std::bitset<1 << CHAR_BIT> CharBits;
    for (size_type i = 0; i != Chars.size(); ++i)
      CharBits.set((unsigned char)Chars[i]);
  
    for (size_type i = std::min(From, Length), e = Length; i != e; ++i)
      if (CharBits.test((unsigned char)Data[i]))
        return i;
    return npos;
  }
  
  /// find_first_not_of - Find the first character in the string that is not
  /// \arg C or npos if not found.
  StringRef::size_type StringRef::find_first_not_of(char C, size_t From) const {
    for (size_type i = std::min(From, Length), e = Length; i != e; ++i)
      if (Data[i] != C)
        return i;
    return npos;
  }
  
  /// find_first_not_of - Find the first character in the string that is not
  /// in the string \arg Chars, or npos if not found.
  ///
  /// Note: O(size() + Chars.size())
  StringRef::size_type StringRef::find_first_not_of(StringRef Chars,
                                                    size_t From) const {
    std::bitset<1 << CHAR_BIT> CharBits;
    for (size_type i = 0; i != Chars.size(); ++i)
      CharBits.set((unsigned char)Chars[i]);
  
    for (size_type i = std::min(From, Length), e = Length; i != e; ++i)
      if (!CharBits.test((unsigned char)Data[i]))
        return i;
    return npos;
  }
  
  /// find_last_of - Find the last character in the string that is in \arg C,
  /// or npos if not found.
  ///
  /// Note: O(size() + Chars.size())
  StringRef::size_type StringRef::find_last_of(StringRef Chars,
                                               size_t From) const {
    std::bitset<1 << CHAR_BIT> CharBits;
    for (size_type i = 0; i != Chars.size(); ++i)
      CharBits.set((unsigned char)Chars[i]);
  
    for (size_type i = std::min(From, Length) - 1, e = -1; i != e; --i)
      if (CharBits.test((unsigned char)Data[i]))
        return i;
    return npos;
  }
  
  /// find_last_not_of - Find the last character in the string that is not
  /// \arg C, or npos if not found.
  StringRef::size_type StringRef::find_last_not_of(char C, size_t From) const {
    for (size_type i = std::min(From, Length) - 1, e = -1; i != e; --i)
      if (Data[i] != C)
        return i;
    return npos;
  }
  
  /// find_last_not_of - Find the last character in the string that is not in
  /// \arg Chars, or npos if not found.
  ///
  /// Note: O(size() + Chars.size())
  StringRef::size_type StringRef::find_last_not_of(StringRef Chars,
                                                   size_t From) const {
    std::bitset<1 << CHAR_BIT> CharBits;
    for (size_type i = 0, e = Chars.size(); i != e; ++i)
      CharBits.set((unsigned char)Chars[i]);
  
    for (size_type i = std::min(From, Length) - 1, e = -1; i != e; --i)
      if (!CharBits.test((unsigned char)Data[i]))
        return i;
    return npos;
  }
  
  void StringRef::split(SmallVectorImpl<StringRef> &A,
                        StringRef Separators, int MaxSplit,
                        bool KeepEmpty) const {
    StringRef rest = *this;
  
    // rest.data() is used to distinguish cases like "a," that splits into
    // "a" + "" and "a" that splits into "a" + 0.
    for (int splits = 0;
         rest.data() != nullptr && (MaxSplit < 0 || splits < MaxSplit);
         ++splits) {
      std::pair<StringRef, StringRef> p = rest.split(Separators);
  
      if (KeepEmpty || p.first.size() != 0)
        A.push_back(p.first);
      rest = p.second;
    }
    // If we have a tail left, add it.
    if (rest.data() != nullptr && (rest.size() != 0 || KeepEmpty))
      A.push_back(rest);
  }
  
  //===----------------------------------------------------------------------===//
  // Helpful Algorithms
  //===----------------------------------------------------------------------===//
  
  /// count - Return the number of non-overlapped occurrences of \arg Str in
  /// the string.
  size_t StringRef::count(StringRef Str) const {
    size_t Count = 0;
    size_t N = Str.size();
    if (N > Length)
      return 0;
    for (size_t i = 0, e = Length - N + 1; i != e; ++i)
      if (substr(i, N).equals(Str))
        ++Count;
    return Count;
  }
  
  static unsigned GetAutoSenseRadix(StringRef &Str) {
    if (Str.startswith("0x")) {
      Str = Str.substr(2);
      return 16;
    }
  
    if (Str.startswith("0b")) {
      Str = Str.substr(2);
      return 2;
    }
  
    if (Str.startswith("0o")) {
      Str = Str.substr(2);
      return 8;
    }
  
    if (Str.startswith("0"))
      return 8;
  
    return 10;
  }
  
  
  /// GetAsUnsignedInteger - Workhorse method that converts a integer character
  /// sequence of radix up to 36 to an unsigned long long value.
  bool llvm::getAsUnsignedInteger(StringRef Str, unsigned Radix,
                                  unsigned long long &Result) {
    // Autosense radix if not specified.
    if (Radix == 0)
      Radix = GetAutoSenseRadix(Str);
  
    // Empty strings (after the radix autosense) are invalid.
    if (Str.empty()) return true;
  
    // Parse all the bytes of the string given this radix.  Watch for overflow.
    Result = 0;
    while (!Str.empty()) {
      unsigned CharVal;
      if (Str[0] >= '0' && Str[0] <= '9')
        CharVal = Str[0]-'0';
      else if (Str[0] >= 'a' && Str[0] <= 'z')
        CharVal = Str[0]-'a'+10;
      else if (Str[0] >= 'A' && Str[0] <= 'Z')
        CharVal = Str[0]-'A'+10;
      else
        return true;
  
      // If the parsed value is larger than the integer radix, the string is
      // invalid.
      if (CharVal >= Radix)
        return true;
  
      // Add in this character.
      unsigned long long PrevResult = Result;
      Result = Result*Radix+CharVal;
  
      // Check for overflow by shifting back and seeing if bits were lost.
      if (Result/Radix < PrevResult)
        return true;
  
      Str = Str.substr(1);
    }
  
    return false;
  }
  
  bool llvm::getAsSignedInteger(StringRef Str, unsigned Radix,
                                long long &Result) {
    unsigned long long ULLVal;
  
    // Handle positive strings first.
    if (Str.empty() || Str.front() != '-') {
      if (getAsUnsignedInteger(Str, Radix, ULLVal) ||
          // Check for value so large it overflows a signed value.
          (long long)ULLVal < 0)
        return true;
      Result = ULLVal;
      return false;
    }
  
    // Get the positive part of the value.
    if (getAsUnsignedInteger(Str.substr(1), Radix, ULLVal) ||
        // Reject values so large they'd overflow as negative signed, but allow
        // "-0".  This negates the unsigned so that the negative isn't undefined
        // on signed overflow.
        (long long)-ULLVal > 0)
      return true;
  
    Result = -ULLVal;
    return false;
  }
  
  bool StringRef::getAsInteger(unsigned Radix, APInt &Result) const {
    StringRef Str = *this;
  
    // Autosense radix if not specified.
    if (Radix == 0)
      Radix = GetAutoSenseRadix(Str);
  
    assert(Radix > 1 && Radix <= 36);
  
    // Empty strings (after the radix autosense) are invalid.
    if (Str.empty()) return true;
  
    // Skip leading zeroes.  This can be a significant improvement if
    // it means we don't need > 64 bits.
    while (!Str.empty() && Str.front() == '0')
      Str = Str.substr(1);
  
    // If it was nothing but zeroes....
    if (Str.empty()) {
      Result = APInt(64, 0);
      return false;
    }
  
    // (Over-)estimate the required number of bits.
    unsigned Log2Radix = 0;
    while ((1U << Log2Radix) < Radix) Log2Radix++;
    bool IsPowerOf2Radix = ((1U << Log2Radix) == Radix);
  
    unsigned BitWidth = Log2Radix * Str.size();
    if (BitWidth < Result.getBitWidth())
      BitWidth = Result.getBitWidth(); // don't shrink the result
    else if (BitWidth > Result.getBitWidth())
      Result = Result.zext(BitWidth);
  
    APInt RadixAP, CharAP; // unused unless !IsPowerOf2Radix
    if (!IsPowerOf2Radix) {
      // These must have the same bit-width as Result.
      RadixAP = APInt(BitWidth, Radix);
      CharAP = APInt(BitWidth, 0);
    }
  
    // Parse all the bytes of the string given this radix.
    Result = 0;
    while (!Str.empty()) {
      unsigned CharVal;
      if (Str[0] >= '0' && Str[0] <= '9')
        CharVal = Str[0]-'0';
      else if (Str[0] >= 'a' && Str[0] <= 'z')
        CharVal = Str[0]-'a'+10;
      else if (Str[0] >= 'A' && Str[0] <= 'Z')
        CharVal = Str[0]-'A'+10;
      else
        return true;
  
      // If the parsed value is larger than the integer radix, the string is
      // invalid.
      if (CharVal >= Radix)
        return true;
  
      // Add in this character.
      if (IsPowerOf2Radix) {
        Result <<= Log2Radix;
        Result |= CharVal;
      } else {
        Result *= RadixAP;
        CharAP = CharVal;
        Result += CharAP;
      }
  
      Str = Str.substr(1);
    }
  
    return false;
  }
  
  
  // Implementation of StringRef hashing.
  hash_code llvm::hash_value(StringRef S) {
    return hash_combine_range(S.begin(), S.end());
  }
  