src/base/string_number_conversions.cc

// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/string_number_conversions.h"

#include <ctype.h>
#include <errno.h>
#include <stdlib.h>
#include <wctype.h>

#include <limits>

#include "base/compiler_specific.h"
#include "base/logging.h"
#include "base/third_party/dmg_fp/dmg_fp.h"
#include "base/utf_string_conversions.h"

namespace base {

namespace {

// The following template is used to convert a size in bytes value into an
// unsigned integral type.  For example, if we want to use the unsigned type
// corresponding to int, we can use type MakeUnsigned<sizeof(int)>::Unsigned.
template <size_t size_in_bytes>
struct MakeUnsigned {};

template <>
struct MakeUnsigned<1> {
  typedef uint8 Unsigned;
};

template <>
struct MakeUnsigned<2> {
  typedef uint16 Unsigned;
};

template <>
struct MakeUnsigned<4> {
  typedef uint32 Unsigned;
};

template <>
struct MakeUnsigned<8> {
  typedef uint64 Unsigned;
};

template <typename STR, typename INT>
struct IntToStringT {
  static STR IntToString(INT value) {
    // log10(2) ~= 0.3 bytes needed per bit or per byte log10(2**8) ~= 2.4.
    // So round up to allocate 3 output characters per byte, plus 1 for '-'.
    const int kOutputBufSize = 3 * sizeof(INT) + 1;

    // Allocate the whole string right away, we will right back to front, and
    // then return the substr of what we ended up using.
    STR outbuf(kOutputBufSize, 0);

    // We cannot directly use 'value < 0' as it will generate a warning on
    // unsigned types in certain compilers because such check is meaningless.
    bool is_neg = value < 1 && value != 0;
    // We cannot simply use '-value' as it will generate a warning on unsigned
    // types in certain compilers which treats such operation as invalid.
    typename MakeUnsigned<sizeof(value)>::Unsigned res =
        is_neg ? 0 - value : value;

    for (typename STR::iterator it = outbuf.end();;) {
      DCHECK(it != outbuf.begin());
      --it;
      *it = static_cast<typename STR::value_type>((res % 10) + '0');
      res /= 10;

      // We're done..
      if (res == 0) {
        if (is_neg) {
          DCHECK(it != outbuf.begin());
          --it;
          *it = static_cast<typename STR::value_type>('-');
        }
        return STR(it, outbuf.end());
      }
    }
    NOTREACHED();
    return STR();
  }
};

// Utility to convert a character to a digit in a given base
template<typename CHAR, int BASE, bool BASE_LTE_10> class BaseCharToDigit {
};

// Faster specialization for bases <= 10
template<typename CHAR, int BASE> class BaseCharToDigit<CHAR, BASE, true> {
 public:
  static bool Convert(CHAR c, uint8* digit) {
    if (c >= '0' && c < '0' + BASE) {
      *digit = c - '0';
      return true;
    }
    return false;
  }
};

// Specialization for bases where 10 < base <= 36
template<typename CHAR, int BASE> class BaseCharToDigit<CHAR, BASE, false> {
 public:
  static bool Convert(CHAR c, uint8* digit) {
    if (c >= '0' && c <= '9') {
      *digit = c - '0';
    } else if (c >= 'a' && c < 'a' + BASE - 10) {
      *digit = c - 'a' + 10;
    } else if (c >= 'A' && c < 'A' + BASE - 10) {
      *digit = c - 'A' + 10;
    } else {
      return false;
    }
    return true;
  }
};

template<int BASE, typename CHAR> bool CharToDigit(CHAR c, uint8* digit) {
  return BaseCharToDigit<CHAR, BASE, BASE <= 10>::Convert(c, digit);
}

// There is an IsWhitespace for wchars defined in string_util.h, but it is
// locale independent, whereas the functions we are replacing were
// locale-dependent. TBD what is desired, but for the moment let's not introduce
// a change in behaviour.
template<typename CHAR> class WhitespaceHelper {
};

template<> class WhitespaceHelper<char> {
 public:
  static bool Invoke(char c) {
    return 0 != isspace(static_cast<unsigned char>(c));
  }
};

template<> class WhitespaceHelper<char16> {
 public:
  static bool Invoke(char16 c) {
    return 0 != iswspace(c);
  }
};

template<typename CHAR> bool LocalIsWhitespace(CHAR c) {
  return WhitespaceHelper<CHAR>::Invoke(c);
}

// IteratorRangeToNumberTraits should provide:
//  - a typedef for iterator_type, the iterator type used as input.
//  - a typedef for value_type, the target numeric type.
//  - static functions min, max (returning the minimum and maximum permitted
//    values)
//  - constant kBase, the base in which to interpret the input
template<typename IteratorRangeToNumberTraits>
class IteratorRangeToNumber {
 public:
  typedef IteratorRangeToNumberTraits traits;
  typedef typename traits::iterator_type const_iterator;
  typedef typename traits::value_type value_type;

  // Generalized iterator-range-to-number conversion.
  //
  static bool Invoke(const_iterator begin,
                     const_iterator end,
                     value_type* output) {
    bool valid = true;

    while (begin != end && LocalIsWhitespace(*begin)) {
      valid = false;
      ++begin;
    }

    if (begin != end && *begin == '-') {
      if (!Negative::Invoke(begin + 1, end, output)) {
        valid = false;
      }
      // For unsigned types, any negative value is invalid and will be set to 0.
      if (traits::min() == 0) {
        if (*output != 0) {
          valid = false;
        }
        *output = 0;
      }
    } else {
      if (begin != end && *begin == '+') {
        ++begin;
      }
      if (!Positive::Invoke(begin, end, output)) {
        valid = false;
      }
    }

    return valid;
  }

 private:
  // Sign provides:
  //  - a static function, CheckBounds, that determines whether the next digit
  //    causes an overflow/underflow
  //  - a static function, Increment, that appends the next digit appropriately
  //    according to the sign of the number being parsed.
  template<typename Sign>
  class Base {
   public:
    static bool Invoke(const_iterator begin, const_iterator end,
                       typename traits::value_type* output) {
      *output = 0;

      if (begin == end) {
        return false;
      }

      // Note: no performance difference was found when using template
      // specialization to remove this check in bases other than 16
      if (traits::kBase == 16 && end - begin > 2 && *begin == '0' &&
          (*(begin + 1) == 'x' || *(begin + 1) == 'X')) {
        begin += 2;
      }

      for (const_iterator current = begin; current != end; ++current) {
        uint8 new_digit = 0;

        if (!CharToDigit<traits::kBase>(*current, &new_digit)) {
          return false;
        }

        if (current != begin) {
          if (!Sign::CheckBounds(output, new_digit)) {
            return false;
          }
          *output *= traits::kBase;
        }

        Sign::Increment(new_digit, output);
      }
      return true;
    }
  };

  class Positive : public Base<Positive> {
   public:
    static bool CheckBounds(value_type* output, uint8 new_digit) {
      if (*output > static_cast<value_type>(traits::max() / traits::kBase) ||
          (*output == static_cast<value_type>(traits::max() / traits::kBase) &&
           new_digit > traits::max() % traits::kBase)) {
        *output = traits::max();
        return false;
      }
      return true;
    }
    static void Increment(uint8 increment, value_type* output) {
      *output += increment;
    }
  };

  class Negative : public Base<Negative> {
   public:
    static bool CheckBounds(value_type* output, uint8 new_digit) {
      if (*output < traits::min() / traits::kBase ||
          (*output == traits::min() / traits::kBase &&
           new_digit > 0 - traits::min() % traits::kBase)) {
        *output = traits::min();
        return false;
      }
      return true;
    }
    static void Increment(uint8 increment, value_type* output) {
      *output -= increment;
    }
  };
};

template<typename ITERATOR, typename VALUE, int BASE>
class BaseIteratorRangeToNumberTraits {
 public:
  typedef ITERATOR iterator_type;
  typedef VALUE value_type;
  static value_type min() {
    return std::numeric_limits<value_type>::min();
  }
  static value_type max() {
    return std::numeric_limits<value_type>::max();
  }
  static const int kBase = BASE;
};

template<typename ITERATOR>
class BaseHexIteratorRangeToIntTraits
    : public BaseIteratorRangeToNumberTraits<ITERATOR, int, 16> {
 public:
  // Allow parsing of 0xFFFFFFFF, which is technically an overflow
  static unsigned int max() {
    return std::numeric_limits<unsigned int>::max();
  }
};

typedef BaseHexIteratorRangeToIntTraits<StringPiece::const_iterator>
    HexIteratorRangeToIntTraits;

template<typename STR>
bool HexStringToBytesT(const STR& input, std::vector<uint8>* output) {
  DCHECK_EQ(output->size(), 0u);
  size_t count = input.size();
  if (count == 0 || (count % 2) != 0)
    return false;
  for (uintptr_t i = 0; i < count / 2; ++i) {
    uint8 msb = 0;  // most significant 4 bits
    uint8 lsb = 0;  // least significant 4 bits
    if (!CharToDigit<16>(input[i * 2], &msb) ||
        !CharToDigit<16>(input[i * 2 + 1], &lsb))
      return false;
    output->push_back((msb << 4) | lsb);
  }
  return true;
}

template <typename VALUE, int BASE>
class StringPieceToNumberTraits
    : public BaseIteratorRangeToNumberTraits<StringPiece::const_iterator,
                                             VALUE,
                                             BASE> {};

template <typename VALUE>
bool StringToIntImpl(const StringPiece& input, VALUE* output) {
  return IteratorRangeToNumber<StringPieceToNumberTraits<VALUE, 10> >::Invoke(
      input.begin(), input.end(), output);
}

template <typename VALUE, int BASE>
class StringPiece16ToNumberTraits
    : public BaseIteratorRangeToNumberTraits<StringPiece16::const_iterator,
                                             VALUE,
                                             BASE> {};

template <typename VALUE>
bool String16ToIntImpl(const StringPiece16& input, VALUE* output) {
  return IteratorRangeToNumber<StringPiece16ToNumberTraits<VALUE, 10> >::Invoke(
      input.begin(), input.end(), output);
}

}  // namespace

#define DEFINE_INTEGRAL_TO_STRING_CONVERSIONS(Name, CppType)       \
  std::string Name##ToString(CppType value) {                      \
    return IntToStringT<std::string, CppType>::IntToString(value); \
  }                                                                \
  string16 Name##ToString16(CppType value) {                       \
    return IntToStringT<string16, CppType>::IntToString(value);    \
  }

INTEGRAL_STRING_CONVERSIONS_FOR_EACH(DEFINE_INTEGRAL_TO_STRING_CONVERSIONS)
#undef DEFINE_INTEGRAL_TO_STRING_CONVERSIONS

std::string DoubleToString(double value) {
  // According to g_fmt.cc, it is sufficient to declare a buffer of size 32.
  char buffer[32];
  dmg_fp::g_fmt(buffer, value);
  return std::string(buffer);
}

#define DEFINE_STRING_TO_INTEGRAL_CONVERSIONS(Name, CppType)         \
  bool StringTo##Name(const StringPiece& input, CppType* output) {   \
    return StringToIntImpl(input, output);                           \
  }                                                                  \
  bool StringTo##Name(const StringPiece16& input, CppType* output) { \
    return String16ToIntImpl(input, output);                         \
  }

INTEGRAL_STRING_CONVERSIONS_FOR_EACH(DEFINE_STRING_TO_INTEGRAL_CONVERSIONS)
#undef DEFINE_STRING_TO_INTEGRAL_CONVERSIONS

bool StringToDouble(const std::string& input, double* output) {
  errno = 0;  // Thread-safe?  It is on at least Mac, Linux, and Windows.
  char* endptr = NULL;
  *output = dmg_fp::strtod(input.c_str(), &endptr);

  // Cases to return false:
  //  - If errno is ERANGE, there was an overflow or underflow.
  //  - If the input string is empty, there was nothing to parse.
  //  - If endptr does not point to the end of the string, there are either
  //    characters remaining in the string after a parsed number, or the string
  //    does not begin with a parseable number.  endptr is compared to the
  //    expected end given the string's stated length to correctly catch cases
  //    where the string contains embedded NUL characters.
  //  - If the first character is a space, there was leading whitespace
  return errno == 0 &&
         !input.empty() &&
         input.c_str() + input.length() == endptr &&
         !isspace(input[0]);
}

// Note: if you need to add String16ToDouble, first ask yourself if it's
// really necessary. If it is, probably the best implementation here is to
// convert to 8-bit and then use the 8-bit version.

// Note: if you need to add an iterator range version of StringToDouble, first
// ask yourself if it's really necessary. If it is, probably the best
// implementation here is to instantiate a string and use the string version.

std::string HexEncode(const void* bytes, size_t size) {
  static const char kHexChars[] = "0123456789ABCDEF";

  // Each input byte creates two output hex characters.
  std::string ret(size * 2, '\0');

  for (size_t i = 0; i < size; ++i) {
    char b = reinterpret_cast<const char*>(bytes)[i];
    ret[(i * 2)] = kHexChars[(b >> 4) & 0xf];
    ret[(i * 2) + 1] = kHexChars[b & 0xf];
  }
  return ret;
}

bool HexStringToInt(const StringPiece& input, int* output) {
  return IteratorRangeToNumber<HexIteratorRangeToIntTraits>::Invoke(
    input.begin(), input.end(), output);
}

bool HexStringToBytes(const std::string& input, std::vector<uint8>* output) {
  return HexStringToBytesT(input, output);
}

}  // namespace base