text: // Copyright 2011 the V8 project 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 "src/conversions.h"
  
  #include <limits.h>
  #include <stdarg.h>
  #include <cmath>
  
  #include "src/allocation.h"
  #include "src/assert-scope.h"
  #include "src/char-predicates-inl.h"
  #include "src/codegen.h"
  #include "src/conversions-inl.h"
  #include "src/dtoa.h"
  #include "src/factory.h"
  #include "src/handles.h"
  #include "src/list-inl.h"
  #include "src/strtod.h"
  #include "src/utils.h"
  
  #ifndef _STLP_VENDOR_CSTD
  // STLPort doesn't import fpclassify into the std namespace.
  using std::fpclassify;
  #endif
  
  namespace v8 {
  namespace internal {
  
  
  namespace {
  
  // C++-style iterator adaptor for StringCharacterStream
  // (unlike C++ iterators the end-marker has different type).
  class StringCharacterStreamIterator {
   public:
    class EndMarker {};
  
    explicit StringCharacterStreamIterator(StringCharacterStream* stream);
  
    uint16_t operator*() const;
    void operator++();
    bool operator==(EndMarker const&) const { return end_; }
    bool operator!=(EndMarker const& m) const { return !end_; }
  
   private:
    StringCharacterStream* const stream_;
    uint16_t current_;
    bool end_;
  };
  
  
  StringCharacterStreamIterator::StringCharacterStreamIterator(
      StringCharacterStream* stream) : stream_(stream) {
    ++(*this);
  }
  
  uint16_t StringCharacterStreamIterator::operator*() const {
    return current_;
  }
  
  
  void StringCharacterStreamIterator::operator++() {
    end_ = !stream_->HasMore();
    if (!end_) {
      current_ = stream_->GetNext();
    }
  }
  }  // End anonymous namespace.
  
  
  double StringToDouble(UnicodeCache* unicode_cache,
                        const char* str, int flags, double empty_string_val) {
    // We cast to const uint8_t* here to avoid instantiating the
    // InternalStringToDouble() template for const char* as well.
    const uint8_t* start = reinterpret_cast<const uint8_t*>(str);
    const uint8_t* end = start + StrLength(str);
    return InternalStringToDouble(unicode_cache, start, end, flags,
                                  empty_string_val);
  }
  
  
  double StringToDouble(UnicodeCache* unicode_cache,
                        Vector<const uint8_t> str,
                        int flags,
                        double empty_string_val) {
    // We cast to const uint8_t* here to avoid instantiating the
    // InternalStringToDouble() template for const char* as well.
    const uint8_t* start = reinterpret_cast<const uint8_t*>(str.start());
    const uint8_t* end = start + str.length();
    return InternalStringToDouble(unicode_cache, start, end, flags,
                                  empty_string_val);
  }
  
  
  double StringToDouble(UnicodeCache* unicode_cache,
                        Vector<const uc16> str,
                        int flags,
                        double empty_string_val) {
    const uc16* end = str.start() + str.length();
    return InternalStringToDouble(unicode_cache, str.start(), end, flags,
                                  empty_string_val);
  }
  
  
  // Converts a string into an integer.
  double StringToInt(UnicodeCache* unicode_cache,
                     Vector<const uint8_t> vector,
                     int radix) {
    return InternalStringToInt(
        unicode_cache, vector.start(), vector.start() + vector.length(), radix);
  }
  
  
  double StringToInt(UnicodeCache* unicode_cache,
                     Vector<const uc16> vector,
                     int radix) {
    return InternalStringToInt(
        unicode_cache, vector.start(), vector.start() + vector.length(), radix);
  }
  
  
  const char* DoubleToCString(double v, Vector<char> buffer) {
    switch (fpclassify(v)) {
      case FP_NAN: return "NaN";
      case FP_INFINITE: return (v < 0.0 ? "-Infinity" : "Infinity");
      case FP_ZERO: return "0";
      default: {
        SimpleStringBuilder builder(buffer.start(), buffer.length());
        int decimal_point;
        int sign;
        const int kV8DtoaBufferCapacity = kBase10MaximalLength + 1;
        char decimal_rep[kV8DtoaBufferCapacity];
        int length;
  
        DoubleToAscii(v, DTOA_SHORTEST, 0,
                      Vector<char>(decimal_rep, kV8DtoaBufferCapacity),
                      &sign, &length, &decimal_point);
  
        if (sign) builder.AddCharacter('-');
  
        if (length <= decimal_point && decimal_point <= 21) {
          // ECMA-262 section 9.8.1 step 6.
          builder.AddString(decimal_rep);
          builder.AddPadding('0', decimal_point - length);
  
        } else if (0 < decimal_point && decimal_point <= 21) {
          // ECMA-262 section 9.8.1 step 7.
          builder.AddSubstring(decimal_rep, decimal_point);
          builder.AddCharacter('.');
          builder.AddString(decimal_rep + decimal_point);
  
        } else if (decimal_point <= 0 && decimal_point > -6) {
          // ECMA-262 section 9.8.1 step 8.
          builder.AddString("0.");
          builder.AddPadding('0', -decimal_point);
          builder.AddString(decimal_rep);
  
        } else {
          // ECMA-262 section 9.8.1 step 9 and 10 combined.
          builder.AddCharacter(decimal_rep[0]);
          if (length != 1) {
            builder.AddCharacter('.');
            builder.AddString(decimal_rep + 1);
          }
          builder.AddCharacter('e');
          builder.AddCharacter((decimal_point >= 0) ? '+' : '-');
          int exponent = decimal_point - 1;
          if (exponent < 0) exponent = -exponent;
          builder.AddDecimalInteger(exponent);
        }
        return builder.Finalize();
      }
    }
  }
  
  
  const char* IntToCString(int n, Vector<char> buffer) {
    bool negative = false;
    if (n < 0) {
      // We must not negate the most negative int.
      if (n == kMinInt) return DoubleToCString(n, buffer);
      negative = true;
      n = -n;
    }
    // Build the string backwards from the least significant digit.
    int i = buffer.length();
    buffer[--i] = '\0';
    do {
      buffer[--i] = '0' + (n % 10);
      n /= 10;
    } while (n);
    if (negative) buffer[--i] = '-';
    return buffer.start() + i;
  }
  
  
  char* DoubleToFixedCString(double value, int f) {
    const int kMaxDigitsBeforePoint = 21;
    const double kFirstNonFixed = 1e21;
    const int kMaxDigitsAfterPoint = 20;
    DCHECK(f >= 0);
    DCHECK(f <= kMaxDigitsAfterPoint);
  
    bool negative = false;
    double abs_value = value;
    if (value < 0) {
      abs_value = -value;
      negative = true;
    }
  
    // If abs_value has more than kMaxDigitsBeforePoint digits before the point
    // use the non-fixed conversion routine.
    if (abs_value >= kFirstNonFixed) {
      char arr[100];
      Vector<char> buffer(arr, arraysize(arr));
      return StrDup(DoubleToCString(value, buffer));
    }
  
    // Find a sufficiently precise decimal representation of n.
    int decimal_point;
    int sign;
    // Add space for the '\0' byte.
    const int kDecimalRepCapacity =
        kMaxDigitsBeforePoint + kMaxDigitsAfterPoint + 1;
    char decimal_rep[kDecimalRepCapacity];
    int decimal_rep_length;
    DoubleToAscii(value, DTOA_FIXED, f,
                  Vector<char>(decimal_rep, kDecimalRepCapacity),
                  &sign, &decimal_rep_length, &decimal_point);
  
    // Create a representation that is padded with zeros if needed.
    int zero_prefix_length = 0;
    int zero_postfix_length = 0;
  
    if (decimal_point <= 0) {
      zero_prefix_length = -decimal_point + 1;
      decimal_point = 1;
    }
  
    if (zero_prefix_length + decimal_rep_length < decimal_point + f) {
      zero_postfix_length = decimal_point + f - decimal_rep_length -
                            zero_prefix_length;
    }
  
    unsigned rep_length =
        zero_prefix_length + decimal_rep_length + zero_postfix_length;
    SimpleStringBuilder rep_builder(rep_length + 1);
    rep_builder.AddPadding('0', zero_prefix_length);
    rep_builder.AddString(decimal_rep);
    rep_builder.AddPadding('0', zero_postfix_length);
    char* rep = rep_builder.Finalize();
  
    // Create the result string by appending a minus and putting in a
    // decimal point if needed.
    unsigned result_size = decimal_point + f + 2;
    SimpleStringBuilder builder(result_size + 1);
    if (negative) builder.AddCharacter('-');
    builder.AddSubstring(rep, decimal_point);
    if (f > 0) {
      builder.AddCharacter('.');
      builder.AddSubstring(rep + decimal_point, f);
    }
    DeleteArray(rep);
    return builder.Finalize();
  }
  
  
  static char* CreateExponentialRepresentation(char* decimal_rep,
                                               int exponent,
                                               bool negative,
                                               int significant_digits) {
    bool negative_exponent = false;
    if (exponent < 0) {
      negative_exponent = true;
      exponent = -exponent;
    }
  
    // Leave room in the result for appending a minus, for a period, the
    // letter 'e', a minus or a plus depending on the exponent, and a
    // three digit exponent.
    unsigned result_size = significant_digits + 7;
    SimpleStringBuilder builder(result_size + 1);
  
    if (negative) builder.AddCharacter('-');
    builder.AddCharacter(decimal_rep[0]);
    if (significant_digits != 1) {
      builder.AddCharacter('.');
      builder.AddString(decimal_rep + 1);
      int rep_length = StrLength(decimal_rep);
      builder.AddPadding('0', significant_digits - rep_length);
    }
  
    builder.AddCharacter('e');
    builder.AddCharacter(negative_exponent ? '-' : '+');
    builder.AddDecimalInteger(exponent);
    return builder.Finalize();
  }
  
  
  char* DoubleToExponentialCString(double value, int f) {
    const int kMaxDigitsAfterPoint = 20;
    // f might be -1 to signal that f was undefined in JavaScript.
    DCHECK(f >= -1 && f <= kMaxDigitsAfterPoint);
  
    bool negative = false;
    if (value < 0) {
      value = -value;
      negative = true;
    }
  
    // Find a sufficiently precise decimal representation of n.
    int decimal_point;
    int sign;
    // f corresponds to the digits after the point. There is always one digit
    // before the point. The number of requested_digits equals hence f + 1.
    // And we have to add one character for the null-terminator.
    const int kV8DtoaBufferCapacity = kMaxDigitsAfterPoint + 1 + 1;
    // Make sure that the buffer is big enough, even if we fall back to the
    // shortest representation (which happens when f equals -1).
    DCHECK(kBase10MaximalLength <= kMaxDigitsAfterPoint + 1);
    char decimal_rep[kV8DtoaBufferCapacity];
    int decimal_rep_length;
  
    if (f == -1) {
      DoubleToAscii(value, DTOA_SHORTEST, 0,
                    Vector<char>(decimal_rep, kV8DtoaBufferCapacity),
                    &sign, &decimal_rep_length, &decimal_point);
      f = decimal_rep_length - 1;
    } else {
      DoubleToAscii(value, DTOA_PRECISION, f + 1,
                    Vector<char>(decimal_rep, kV8DtoaBufferCapacity),
                    &sign, &decimal_rep_length, &decimal_point);
    }
    DCHECK(decimal_rep_length > 0);
    DCHECK(decimal_rep_length <= f + 1);
  
    int exponent = decimal_point - 1;
    char* result =
        CreateExponentialRepresentation(decimal_rep, exponent, negative, f+1);
  
    return result;
  }
  
  
  char* DoubleToPrecisionCString(double value, int p) {
    const int kMinimalDigits = 1;
    const int kMaximalDigits = 21;
    DCHECK(p >= kMinimalDigits && p <= kMaximalDigits);
    USE(kMinimalDigits);
  
    bool negative = false;
    if (value < 0) {
      value = -value;
      negative = true;
    }
  
    // Find a sufficiently precise decimal representation of n.
    int decimal_point;
    int sign;
    // Add one for the terminating null character.
    const int kV8DtoaBufferCapacity = kMaximalDigits + 1;
    char decimal_rep[kV8DtoaBufferCapacity];
    int decimal_rep_length;
  
    DoubleToAscii(value, DTOA_PRECISION, p,
                  Vector<char>(decimal_rep, kV8DtoaBufferCapacity),
                  &sign, &decimal_rep_length, &decimal_point);
    DCHECK(decimal_rep_length <= p);
  
    int exponent = decimal_point - 1;
  
    char* result = NULL;
  
    if (exponent < -6 || exponent >= p) {
      result =
          CreateExponentialRepresentation(decimal_rep, exponent, negative, p);
    } else {
      // Use fixed notation.
      //
      // Leave room in the result for appending a minus, a period and in
      // the case where decimal_point is not positive for a zero in
      // front of the period.
      unsigned result_size = (decimal_point <= 0)
          ? -decimal_point + p + 3
          : p + 2;
      SimpleStringBuilder builder(result_size + 1);
      if (negative) builder.AddCharacter('-');
      if (decimal_point <= 0) {
        builder.AddString("0.");
        builder.AddPadding('0', -decimal_point);
        builder.AddString(decimal_rep);
        builder.AddPadding('0', p - decimal_rep_length);
      } else {
        const int m = Min(decimal_rep_length, decimal_point);
        builder.AddSubstring(decimal_rep, m);
        builder.AddPadding('0', decimal_point - decimal_rep_length);
        if (decimal_point < p) {
          builder.AddCharacter('.');
          const int extra = negative ? 2 : 1;
          if (decimal_rep_length > decimal_point) {
            const int len = StrLength(decimal_rep + decimal_point);
            const int n = Min(len, p - (builder.position() - extra));
            builder.AddSubstring(decimal_rep + decimal_point, n);
          }
          builder.AddPadding('0', extra + (p - builder.position()));
        }
      }
      result = builder.Finalize();
    }
  
    return result;
  }
  
  char* DoubleToRadixCString(double value, int radix) {
    DCHECK(radix >= 2 && radix <= 36);
    DCHECK(std::isfinite(value));
    DCHECK_NE(0.0, value);
    // Character array used for conversion.
    static const char chars[] = "0123456789abcdefghijklmnopqrstuvwxyz";
  
    // Temporary buffer for the result. We start with the decimal point in the
    // middle and write to the left for the integer part and to the right for the
    // fractional part. 1024 characters for the exponent and 52 for the mantissa
    // either way, with additional space for sign, decimal point and string
    // termination should be sufficient.
    static const int kBufferSize = 2200;
    char buffer[kBufferSize];
    int integer_cursor = kBufferSize / 2;
    int fraction_cursor = integer_cursor;
  
    bool negative = value < 0;
    if (negative) value = -value;
  
    // Split the value into an integer part and a fractional part.
    double integer = std::floor(value);
    double fraction = value - integer;
    // We only compute fractional digits up to the input double's precision.
    double delta = 0.5 * (Double(value).NextDouble() - value);
    delta = std::max(Double(0.0).NextDouble(), delta);
    DCHECK_GT(delta, 0.0);
    if (fraction > delta) {
      // Insert decimal point.
      buffer[fraction_cursor++] = '.';
      do {
        // Shift up by one digit.
        fraction *= radix;
        delta *= radix;
        // Write digit.
        int digit = static_cast<int>(fraction);
        buffer[fraction_cursor++] = chars[digit];
        // Calculate remainder.
        fraction -= digit;
        // Round to even.
        if (fraction > 0.5 || (fraction == 0.5 && (digit & 1))) {
          if (fraction + delta > 1) {
            // We need to back trace already written digits in case of carry-over.
            while (true) {
              fraction_cursor--;
              if (fraction_cursor == kBufferSize / 2) {
                CHECK_EQ('.', buffer[fraction_cursor]);
                // Carry over to the integer part.
                integer += 1;
                break;
              }
              char c = buffer[fraction_cursor];
              // Reconstruct digit.
              int digit = c > '9' ? (c - 'a' + 10) : (c - '0');
              if (digit + 1 < radix) {
                buffer[fraction_cursor++] = chars[digit + 1];
                break;
              }
            }
            break;
          }
        }
      } while (fraction > delta);
    }
  
    // Compute integer digits. Fill unrepresented digits with zero.
    while (Double(integer / radix).Exponent() > 0) {
      integer /= radix;
      buffer[--integer_cursor] = '0';
    }
    do {
      double remainder = modulo(integer, radix);
      buffer[--integer_cursor] = chars[static_cast<int>(remainder)];
      integer = (integer - remainder) / radix;
    } while (integer > 0);
  
    // Add sign and terminate string.
    if (negative) buffer[--integer_cursor] = '-';
    buffer[fraction_cursor++] = '\0';
    DCHECK_LT(fraction_cursor, kBufferSize);
    DCHECK_LE(0, integer_cursor);
    // Allocate new string as return value.
    char* result = NewArray<char>(fraction_cursor - integer_cursor);
    memcpy(result, buffer + integer_cursor, fraction_cursor - integer_cursor);
    return result;
  }
  
  
  // ES6 18.2.4 parseFloat(string)
  double StringToDouble(UnicodeCache* unicode_cache, Handle<String> string,
                        int flags, double empty_string_val) {
    Handle<String> flattened = String::Flatten(string);
    {
      DisallowHeapAllocation no_gc;
      String::FlatContent flat = flattened->GetFlatContent();
      DCHECK(flat.IsFlat());
      if (flat.IsOneByte()) {
        return StringToDouble(unicode_cache, flat.ToOneByteVector(), flags,
                              empty_string_val);
      } else {
        return StringToDouble(unicode_cache, flat.ToUC16Vector(), flags,
                              empty_string_val);
      }
    }
  }
  
  
  bool IsSpecialIndex(UnicodeCache* unicode_cache, String* string) {
    // Max length of canonical double: -X.XXXXXXXXXXXXXXXXX-eXXX
    const int kBufferSize = 24;
    const int length = string->length();
    if (length == 0 || length > kBufferSize) return false;
    uint16_t buffer[kBufferSize];
    String::WriteToFlat(string, buffer, 0, length);
    // If the first char is not a digit or a '-' or we can't match 'NaN' or
    // '(-)Infinity', bailout immediately.
    int offset = 0;
    if (!IsDecimalDigit(buffer[0])) {
      if (buffer[0] == '-') {
        if (length == 1) return false;  // Just '-' is bad.
        if (!IsDecimalDigit(buffer[1])) {
          if (buffer[1] == 'I' && length == 9) {
            // Allow matching of '-Infinity' below.
          } else {
            return false;
          }
        }
        offset++;
      } else if (buffer[0] == 'I' && length == 8) {
        // Allow matching of 'Infinity' below.
      } else if (buffer[0] == 'N' && length == 3) {
        // Match NaN.
        return buffer[1] == 'a' && buffer[2] == 'N';
      } else {
        return false;
      }
    }
    // Expected fast path: key is an integer.
    static const int kRepresentableIntegerLength = 15;  // (-)XXXXXXXXXXXXXXX
    if (length - offset <= kRepresentableIntegerLength) {
      const int initial_offset = offset;
      bool matches = true;
      for (; offset < length; offset++) {
        matches &= IsDecimalDigit(buffer[offset]);
      }
      if (matches) {
        // Match 0 and -0.
        if (buffer[initial_offset] == '0') return initial_offset == length - 1;
        return true;
      }
    }
    // Slow path: test DoubleToString(StringToDouble(string)) == string.
    Vector<const uint16_t> vector(buffer, length);
    double d = StringToDouble(unicode_cache, vector, NO_FLAGS);
    if (std::isnan(d)) return false;
    // Compute reverse string.
    char reverse_buffer[kBufferSize + 1];  // Result will be /0 terminated.
    Vector<char> reverse_vector(reverse_buffer, arraysize(reverse_buffer));
    const char* reverse_string = DoubleToCString(d, reverse_vector);
    for (int i = 0; i < length; ++i) {
      if (static_cast<uint16_t>(reverse_string[i]) != buffer[i]) return false;
    }
    return true;
  }
  }  // namespace internal
  }  // namespace v8
  