v8/src/conversions.cc

// 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