lib/Support/StringRef.cpp

//===-- 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"

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;
}

/// compare_lower - Compare strings, ignoring case.
int StringRef::compare_lower(StringRef RHS) const {
  for (size_t I = 0, E = min(Length, RHS.Length); I != E; ++I) {
    char LHC = ascii_tolower(Data[I]);
    char RHC = ascii_tolower(RHS.Data[I]);
    if (LHC != RHC)
      return LHC < RHC ? -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) {
  // The algorithm implemented below is the "classic"
  // dynamic-programming algorithm for computing the Levenshtein
  // distance, which is described here:
  //
  //   http://en.wikipedia.org/wiki/Levenshtein_distance
  //
  // Although the algorithm is typically described using an m x n
  // array, only two rows are used at a time, so this implemenation
  // just keeps two separate vectors for those two rows.
  size_type m = size();
  size_type n = Other.size();

  const unsigned SmallBufferSize = 64;
  unsigned SmallBuffer[SmallBufferSize];
  unsigned *Allocated = 0;
  unsigned *previous = SmallBuffer;
  if (2*(n + 1) > SmallBufferSize)
    Allocated = previous = new unsigned [2*(n+1)];
  unsigned *current = previous + (n + 1);
  
  for (unsigned i = 0; i <= n; ++i) 
    previous[i] = i;

  for (size_type y = 1; y <= m; ++y) {
    current[0] = y;
    for (size_type x = 1; x <= n; ++x) {
      if (AllowReplacements) {
        current[x] = min(previous[x-1] + ((*this)[y-1] == Other[x-1]? 0u:1u),
                         min(current[x-1], previous[x])+1);
      }
      else {
        if ((*this)[y-1] == Other[x-1]) current[x] = previous[x-1];
        else current[x] = min(current[x-1], previous[x]) + 1;
      }
    }
    
    unsigned *tmp = current;
    current = previous;
    previous = tmp;
  }

  unsigned Result = previous[n];
  delete [] Allocated;
  
  return Result;
}

//===----------------------------------------------------------------------===//
// String Searching
//===----------------------------------------------------------------------===//


/// find - Search for the first string \arg Str in the string.
///
/// \return - The index of the first occurence 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 (size_t e = Length - N + 1, i = min(From, e); i != e; ++i)
    if (substr(i, N).equals(Str))
      return i;
  return npos;
}

/// rfind - Search for the last string \arg Str in the string.
///
/// \return - The index of the last occurence 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 {
  for (size_type i = min(From, Length), e = Length; i != e; ++i)
    if (Chars.find(Data[i]) != npos)
      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 = 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 {
  for (size_type i = min(From, Length), e = Length; i != e; ++i)
    if (Chars.find(Data[i]) == npos)
      return i;
  return npos;
}


//===----------------------------------------------------------------------===//
// 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;
  } else if (Str.startswith("0b")) {
    Str = Str.substr(2);
    return 2;
  } else if (Str.startswith("0")) {
    return 8;
  } else {
    return 10;
  }
}


/// GetAsUnsignedInteger - Workhorse method that converts a integer character
/// sequence of radix up to 36 to an unsigned long long value.
static bool 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.
    if (Result < PrevResult)
      return true;

    Str = Str.substr(1);
  }
  
  return false;
}

bool StringRef::getAsInteger(unsigned Radix, unsigned long long &Result) const {
  return GetAsUnsignedInteger(*this, Radix, Result);
}


bool StringRef::getAsInteger(unsigned Radix, long long &Result) const {
  unsigned long long ULLVal;
  
  // Handle positive strings first.
  if (empty() || front() != '-') {
    if (GetAsUnsignedInteger(*this, 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(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, int &Result) const {
  long long Val;
  if (getAsInteger(Radix, Val) ||
      (int)Val != Val)
    return true;
  Result = Val;
  return false;
}

bool StringRef::getAsInteger(unsigned Radix, unsigned &Result) const {
  unsigned long long Val;
  if (getAsInteger(Radix, Val) ||
      (unsigned)Val != Val)
    return true;
  Result = Val;
  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
    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;
}