The Tor Browser: comparison mfbt/double-conversion/double-conversion.h

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+:7c17ccee2b4f
+// Copyright 2012 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#ifndef DOUBLE_CONVERSION_DOUBLE_CONVERSION_H_
+#define DOUBLE_CONVERSION_DOUBLE_CONVERSION_H_
+#include "mozilla/Types.h"
+#include "utils.h"
+namespace double_conversion {
+class DoubleToStringConverter {
+public:
+// When calling ToFixed with a double > 10^kMaxFixedDigitsBeforePoint
+// or a requested_digits parameter > kMaxFixedDigitsAfterPoint then the
+// function returns false.
+static const int kMaxFixedDigitsBeforePoint = 60;
+static const int kMaxFixedDigitsAfterPoint = 60;
+// When calling ToExponential with a requested_digits
+// parameter > kMaxExponentialDigits then the function returns false.
+static const int kMaxExponentialDigits = 120;
+// When calling ToPrecision with a requested_digits
+// parameter < kMinPrecisionDigits or requested_digits > kMaxPrecisionDigits
+// then the function returns false.
+static const int kMinPrecisionDigits = 1;
+static const int kMaxPrecisionDigits = 120;
+enum Flags {
+NO_FLAGS = 0,
+EMIT_POSITIVE_EXPONENT_SIGN = 1,
+EMIT_TRAILING_DECIMAL_POINT = 2,
+EMIT_TRAILING_ZERO_AFTER_POINT = 4,
+UNIQUE_ZERO = 8
+};
+// Flags should be a bit-or combination of the possible Flags-enum.
+//  - NO_FLAGS: no special flags.
+//  - EMIT_POSITIVE_EXPONENT_SIGN: when the number is converted into exponent
+//    form, emits a '+' for positive exponents. Example: 1.2e+2.
+//  - EMIT_TRAILING_DECIMAL_POINT: when the input number is an integer and is
+//    converted into decimal format then a trailing decimal point is appended.
+//    Example: 2345.0 is converted to "2345.".
+//  - EMIT_TRAILING_ZERO_AFTER_POINT: in addition to a trailing decimal point
+//    emits a trailing '0'-character. This flag requires the
+//    EXMIT_TRAILING_DECIMAL_POINT flag.
+//    Example: 2345.0 is converted to "2345.0".
+//  - UNIQUE_ZERO: "-0.0" is converted to "0.0".
+//
+// Infinity symbol and nan_symbol provide the string representation for these
+// special values. If the string is NULL and the special value is encountered
+// then the conversion functions return false.
+//
+// The exponent_character is used in exponential representations. It is
+// usually 'e' or 'E'.
+//
+// When converting to the shortest representation the converter will
+// represent input numbers in decimal format if they are in the interval
+// [10^decimal_in_shortest_low; 10^decimal_in_shortest_high[
+//    (lower boundary included, greater boundary excluded).
+// Example: with decimal_in_shortest_low = -6 and
+//               decimal_in_shortest_high = 21:
+//   ToShortest(0.000001)  -> "0.000001"
+//   ToShortest(0.0000001) -> "1e-7"
+//   ToShortest(111111111111111111111.0)  -> "111111111111111110000"
+//   ToShortest(100000000000000000000.0)  -> "100000000000000000000"
+//   ToShortest(1111111111111111111111.0) -> "1.1111111111111111e+21"
+//
+// When converting to precision mode the converter may add
+// max_leading_padding_zeroes before returning the number in exponential
+// format.
+// Example with max_leading_padding_zeroes_in_precision_mode = 6.
+//   ToPrecision(0.0000012345, 2) -> "0.0000012"
+//   ToPrecision(0.00000012345, 2) -> "1.2e-7"
+// Similarily the converter may add up to
+// max_trailing_padding_zeroes_in_precision_mode in precision mode to avoid
+// returning an exponential representation. A zero added by the
+// EMIT_TRAILING_ZERO_AFTER_POINT flag is counted for this limit.
+// Examples for max_trailing_padding_zeroes_in_precision_mode = 1:
+//   ToPrecision(230.0, 2) -> "230"
+//   ToPrecision(230.0, 2) -> "230."  with EMIT_TRAILING_DECIMAL_POINT.
+//   ToPrecision(230.0, 2) -> "2.3e2" with EMIT_TRAILING_ZERO_AFTER_POINT.
+DoubleToStringConverter(int flags,
+const char* infinity_symbol,
+const char* nan_symbol,
+char exponent_character,
+int decimal_in_shortest_low,
+int decimal_in_shortest_high,
+int max_leading_padding_zeroes_in_precision_mode,
+int max_trailing_padding_zeroes_in_precision_mode)
+: flags_(flags),
+infinity_symbol_(infinity_symbol),
+nan_symbol_(nan_symbol),
+exponent_character_(exponent_character),
+decimal_in_shortest_low_(decimal_in_shortest_low),
+decimal_in_shortest_high_(decimal_in_shortest_high),
+max_leading_padding_zeroes_in_precision_mode_(
+max_leading_padding_zeroes_in_precision_mode),
+max_trailing_padding_zeroes_in_precision_mode_(
+max_trailing_padding_zeroes_in_precision_mode) {
+// When 'trailing zero after the point' is set, then 'trailing point'
+// must be set too.
+ASSERT(((flags & EMIT_TRAILING_DECIMAL_POINT) != 0) ||
+!((flags & EMIT_TRAILING_ZERO_AFTER_POINT) != 0));
+}
+// Returns a converter following the EcmaScript specification.
+static MFBT_API const DoubleToStringConverter& EcmaScriptConverter();
+// Computes the shortest string of digits that correctly represent the input
+// number. Depending on decimal_in_shortest_low and decimal_in_shortest_high
+// (see constructor) it then either returns a decimal representation, or an
+// exponential representation.
+// Example with decimal_in_shortest_low = -6,
+//              decimal_in_shortest_high = 21,
+//              EMIT_POSITIVE_EXPONENT_SIGN activated, and
+//              EMIT_TRAILING_DECIMAL_POINT deactived:
+//   ToShortest(0.000001)  -> "0.000001"
+//   ToShortest(0.0000001) -> "1e-7"
+//   ToShortest(111111111111111111111.0)  -> "111111111111111110000"
+//   ToShortest(100000000000000000000.0)  -> "100000000000000000000"
+//   ToShortest(1111111111111111111111.0) -> "1.1111111111111111e+21"
+//
+// Note: the conversion may round the output if the returned string
+// is accurate enough to uniquely identify the input-number.
+// For example the most precise representation of the double 9e59 equals
+// "899999999999999918767229449717619953810131273674690656206848", but
+// the converter will return the shorter (but still correct) "9e59".
+//
+// Returns true if the conversion succeeds. The conversion always succeeds
+// except when the input value is special and no infinity_symbol or
+// nan_symbol has been given to the constructor.
+bool ToShortest(double value, StringBuilder* result_builder) const {
+return ToShortestIeeeNumber(value, result_builder, SHORTEST);
+}
+// Same as ToShortest, but for single-precision floats.
+bool ToShortestSingle(float value, StringBuilder* result_builder) const {
+return ToShortestIeeeNumber(value, result_builder, SHORTEST_SINGLE);
+}
+// Computes a decimal representation with a fixed number of digits after the
+// decimal point. The last emitted digit is rounded.
+//
+// Examples:
+//   ToFixed(3.12, 1) -> "3.1"
+//   ToFixed(3.1415, 3) -> "3.142"
+//   ToFixed(1234.56789, 4) -> "1234.5679"
+//   ToFixed(1.23, 5) -> "1.23000"
+//   ToFixed(0.1, 4) -> "0.1000"
+//   ToFixed(1e30, 2) -> "1000000000000000019884624838656.00"
+//   ToFixed(0.1, 30) -> "0.100000000000000005551115123126"
+//   ToFixed(0.1, 17) -> "0.10000000000000001"
+//
+// If requested_digits equals 0, then the tail of the result depends on
+// the EMIT_TRAILING_DECIMAL_POINT and EMIT_TRAILING_ZERO_AFTER_POINT.
+// Examples, for requested_digits == 0,
+//   let EMIT_TRAILING_DECIMAL_POINT and EMIT_TRAILING_ZERO_AFTER_POINT be
+//    - false and false: then 123.45 -> 123
+//                             0.678 -> 1
+//    - true and false: then 123.45 -> 123.
+//                            0.678 -> 1.
+//    - true and true: then 123.45 -> 123.0
+//                           0.678 -> 1.0
+//
+// Returns true if the conversion succeeds. The conversion always succeeds
+// except for the following cases:
+//   - the input value is special and no infinity_symbol or nan_symbol has
+//     been provided to the constructor,
+//   - 'value' > 10^kMaxFixedDigitsBeforePoint, or
+//   - 'requested_digits' > kMaxFixedDigitsAfterPoint.
+// The last two conditions imply that the result will never contain more than
+// 1 + kMaxFixedDigitsBeforePoint + 1 + kMaxFixedDigitsAfterPoint characters
+// (one additional character for the sign, and one for the decimal point).
+MFBT_API bool ToFixed(double value,
+int requested_digits,
+StringBuilder* result_builder) const;
+// Computes a representation in exponential format with requested_digits
+// after the decimal point. The last emitted digit is rounded.
+// If requested_digits equals -1, then the shortest exponential representation
+// is computed.
+//
+// Examples with EMIT_POSITIVE_EXPONENT_SIGN deactivated, and
+//               exponent_character set to 'e'.
+//   ToExponential(3.12, 1) -> "3.1e0"
+//   ToExponential(5.0, 3) -> "5.000e0"
+//   ToExponential(0.001, 2) -> "1.00e-3"
+//   ToExponential(3.1415, -1) -> "3.1415e0"
+//   ToExponential(3.1415, 4) -> "3.1415e0"
+//   ToExponential(3.1415, 3) -> "3.142e0"
+//   ToExponential(123456789000000, 3) -> "1.235e14"
+//   ToExponential(1000000000000000019884624838656.0, -1) -> "1e30"
+//   ToExponential(1000000000000000019884624838656.0, 32) ->
+//                     "1.00000000000000001988462483865600e30"
+//   ToExponential(1234, 0) -> "1e3"
+//
+// Returns true if the conversion succeeds. The conversion always succeeds
+// except for the following cases:
+//   - the input value is special and no infinity_symbol or nan_symbol has
+//     been provided to the constructor,
+//   - 'requested_digits' > kMaxExponentialDigits.
+// The last condition implies that the result will never contain more than
+// kMaxExponentialDigits + 8 characters (the sign, the digit before the
+// decimal point, the decimal point, the exponent character, the
+// exponent's sign, and at most 3 exponent digits).
+MFBT_API bool ToExponential(double value,
+int requested_digits,
+StringBuilder* result_builder) const;
+// Computes 'precision' leading digits of the given 'value' and returns them
+// either in exponential or decimal format, depending on
+// max_{leading|trailing}_padding_zeroes_in_precision_mode (given to the
+// constructor).
+// The last computed digit is rounded.
+//
+// Example with max_leading_padding_zeroes_in_precision_mode = 6.
+//   ToPrecision(0.0000012345, 2) -> "0.0000012"
+//   ToPrecision(0.00000012345, 2) -> "1.2e-7"
+// Similarily the converter may add up to
+// max_trailing_padding_zeroes_in_precision_mode in precision mode to avoid
+// returning an exponential representation. A zero added by the
+// EMIT_TRAILING_ZERO_AFTER_POINT flag is counted for this limit.
+// Examples for max_trailing_padding_zeroes_in_precision_mode = 1:
+//   ToPrecision(230.0, 2) -> "230"
+//   ToPrecision(230.0, 2) -> "230."  with EMIT_TRAILING_DECIMAL_POINT.
+//   ToPrecision(230.0, 2) -> "2.3e2" with EMIT_TRAILING_ZERO_AFTER_POINT.
+// Examples for max_trailing_padding_zeroes_in_precision_mode = 3, and no
+//    EMIT_TRAILING_ZERO_AFTER_POINT:
+//   ToPrecision(123450.0, 6) -> "123450"
+//   ToPrecision(123450.0, 5) -> "123450"
+//   ToPrecision(123450.0, 4) -> "123500"
+//   ToPrecision(123450.0, 3) -> "123000"
+//   ToPrecision(123450.0, 2) -> "1.2e5"
+//
+// Returns true if the conversion succeeds. The conversion always succeeds
+// except for the following cases:
+//   - the input value is special and no infinity_symbol or nan_symbol has
+//     been provided to the constructor,
+//   - precision < kMinPericisionDigits
+//   - precision > kMaxPrecisionDigits
+// The last condition implies that the result will never contain more than
+// kMaxPrecisionDigits + 7 characters (the sign, the decimal point, the
+// exponent character, the exponent's sign, and at most 3 exponent digits).
+MFBT_API bool ToPrecision(double value,
+int precision,
+bool* used_exponential_notation,
+StringBuilder* result_builder) const;
+enum DtoaMode {
+// Produce the shortest correct representation.
+// For example the output of 0.299999999999999988897 is (the less accurate
+// but correct) 0.3.
+SHORTEST,
+// Same as SHORTEST, but for single-precision floats.
+SHORTEST_SINGLE,
+// Produce a fixed number of digits after the decimal point.
+// For instance fixed(0.1, 4) becomes 0.1000
+// If the input number is big, the output will be big.
+FIXED,
+// Fixed number of digits (independent of the decimal point).
+PRECISION
+};
+// The maximal number of digits that are needed to emit a double in base 10.
+// A higher precision can be achieved by using more digits, but the shortest
+// accurate representation of any double will never use more digits than
+// kBase10MaximalLength.
+// Note that DoubleToAscii null-terminates its input. So the given buffer
+// should be at least kBase10MaximalLength + 1 characters long.
+static const MFBT_DATA int kBase10MaximalLength = 17;
+// Converts the given double 'v' to ascii. 'v' must not be NaN, +Infinity, or
+// -Infinity. In SHORTEST_SINGLE-mode this restriction also applies to 'v'
+// after it has been casted to a single-precision float. That is, in this
+// mode static_cast<float>(v) must not be NaN, +Infinity or -Infinity.
+//
+// The result should be interpreted as buffer * 10^(point-length).
+//
+// The output depends on the given mode:
+//  - SHORTEST: produce the least amount of digits for which the internal
+//   identity requirement is still satisfied. If the digits are printed
+//   (together with the correct exponent) then reading this number will give
+//   'v' again. The buffer will choose the representation that is closest to
+//   'v'. If there are two at the same distance, than the one farther away
+//   from 0 is chosen (halfway cases - ending with 5 - are rounded up).
+//   In this mode the 'requested_digits' parameter is ignored.
+//  - SHORTEST_SINGLE: same as SHORTEST but with single-precision.
+//  - FIXED: produces digits necessary to print a given number with
+//   'requested_digits' digits after the decimal point. The produced digits
+//   might be too short in which case the caller has to fill the remainder
+//   with '0's.
+//   Example: toFixed(0.001, 5) is allowed to return buffer="1", point=-2.
+//   Halfway cases are rounded towards +/-Infinity (away from 0). The call
+//   toFixed(0.15, 2) thus returns buffer="2", point=0.
+//   The returned buffer may contain digits that would be truncated from the
+//   shortest representation of the input.
+//  - PRECISION: produces 'requested_digits' where the first digit is not '0'.
+//   Even though the length of produced digits usually equals
+//   'requested_digits', the function is allowed to return fewer digits, in
+//   which case the caller has to fill the missing digits with '0's.
+//   Halfway cases are again rounded away from 0.
+// DoubleToAscii expects the given buffer to be big enough to hold all
+// digits and a terminating null-character. In SHORTEST-mode it expects a
+// buffer of at least kBase10MaximalLength + 1. In all other modes the
+// requested_digits parameter and the padding-zeroes limit the size of the
+// output. Don't forget the decimal point, the exponent character and the
+// terminating null-character when computing the maximal output size.
+// The given length is only used in debug mode to ensure the buffer is big
+// enough.
+static MFBT_API void DoubleToAscii(double v,
+DtoaMode mode,
+int requested_digits,
+char* buffer,
+int buffer_length,
+bool* sign,
+int* length,
+int* point);
+private:
+// Implementation for ToShortest and ToShortestSingle.
+MFBT_API bool ToShortestIeeeNumber(double value,
+StringBuilder* result_builder,
+DtoaMode mode) const;
+// If the value is a special value (NaN or Infinity) constructs the
+// corresponding string using the configured infinity/nan-symbol.
+// If either of them is NULL or the value is not special then the
+// function returns false.
+MFBT_API bool HandleSpecialValues(double value, StringBuilder* result_builder) const;
+// Constructs an exponential representation (i.e. 1.234e56).
+// The given exponent assumes a decimal point after the first decimal digit.
+MFBT_API void CreateExponentialRepresentation(const char* decimal_digits,
+int length,
+int exponent,
+StringBuilder* result_builder) const;
+// Creates a decimal representation (i.e 1234.5678).
+MFBT_API void CreateDecimalRepresentation(const char* decimal_digits,
+int length,
+int decimal_point,
+int digits_after_point,
+StringBuilder* result_builder) const;
+const int flags_;
+const char* const infinity_symbol_;
+const char* const nan_symbol_;
+const char exponent_character_;
+const int decimal_in_shortest_low_;
+const int decimal_in_shortest_high_;
+const int max_leading_padding_zeroes_in_precision_mode_;
+const int max_trailing_padding_zeroes_in_precision_mode_;
+DISALLOW_IMPLICIT_CONSTRUCTORS(DoubleToStringConverter);
+};
+class StringToDoubleConverter {
+public:
+// Enumeration for allowing octals and ignoring junk when converting
+// strings to numbers.
+enum Flags {
+NO_FLAGS = 0,
+ALLOW_HEX = 1,
+ALLOW_OCTALS = 2,
+ALLOW_TRAILING_JUNK = 4,
+ALLOW_LEADING_SPACES = 8,
+ALLOW_TRAILING_SPACES = 16,
+ALLOW_SPACES_AFTER_SIGN = 32
+};
+// Flags should be a bit-or combination of the possible Flags-enum.
+//  - NO_FLAGS: no special flags.
+//  - ALLOW_HEX: recognizes the prefix "0x". Hex numbers may only be integers.
+//      Ex: StringToDouble("0x1234") -> 4660.0
+//          In StringToDouble("0x1234.56") the characters ".56" are trailing
+//          junk. The result of the call is hence dependent on
+//          the ALLOW_TRAILING_JUNK flag and/or the junk value.
+//      With this flag "0x" is a junk-string. Even with ALLOW_TRAILING_JUNK,
+//      the string will not be parsed as "0" followed by junk.
+//
+//  - ALLOW_OCTALS: recognizes the prefix "0" for octals:
+//      If a sequence of octal digits starts with '0', then the number is
+//      read as octal integer. Octal numbers may only be integers.
+//      Ex: StringToDouble("01234") -> 668.0
+//          StringToDouble("012349") -> 12349.0  // Not a sequence of octal
+//                                               // digits.
+//          In StringToDouble("01234.56") the characters ".56" are trailing
+//          junk. The result of the call is hence dependent on
+//          the ALLOW_TRAILING_JUNK flag and/or the junk value.
+//          In StringToDouble("01234e56") the characters "e56" are trailing
+//          junk, too.
+//  - ALLOW_TRAILING_JUNK: ignore trailing characters that are not part of
+//      a double literal.
+//  - ALLOW_LEADING_SPACES: skip over leading spaces.
+//  - ALLOW_TRAILING_SPACES: ignore trailing spaces.
+//  - ALLOW_SPACES_AFTER_SIGN: ignore spaces after the sign.
+//       Ex: StringToDouble("-   123.2") -> -123.2.
+//           StringToDouble("+   123.2") -> 123.2
+//
+// empty_string_value is returned when an empty string is given as input.
+// If ALLOW_LEADING_SPACES or ALLOW_TRAILING_SPACES are set, then a string
+// containing only spaces is converted to the 'empty_string_value', too.
+//
+// junk_string_value is returned when
+//  a) ALLOW_TRAILING_JUNK is not set, and a junk character (a character not
+//     part of a double-literal) is found.
+//  b) ALLOW_TRAILING_JUNK is set, but the string does not start with a
+//     double literal.
+//
+// infinity_symbol and nan_symbol are strings that are used to detect
+// inputs that represent infinity and NaN. They can be null, in which case
+// they are ignored.
+// The conversion routine first reads any possible signs. Then it compares the
+// following character of the input-string with the first character of
+// the infinity, and nan-symbol. If either matches, the function assumes, that
+// a match has been found, and expects the following input characters to match
+// the remaining characters of the special-value symbol.
+// This means that the following restrictions apply to special-value symbols:
+//  - they must not start with signs ('+', or '-'),
+//  - they must not have the same first character.
+//  - they must not start with digits.
+//
+// Examples:
+//  flags = ALLOW_HEX | ALLOW_TRAILING_JUNK,
+//  empty_string_value = 0.0,
+//  junk_string_value = NaN,
+//  infinity_symbol = "infinity",
+//  nan_symbol = "nan":
+//    StringToDouble("0x1234") -> 4660.0.
+//    StringToDouble("0x1234K") -> 4660.0.
+//    StringToDouble("") -> 0.0  // empty_string_value.
+//    StringToDouble(" ") -> NaN  // junk_string_value.
+//    StringToDouble(" 1") -> NaN  // junk_string_value.
+//    StringToDouble("0x") -> NaN  // junk_string_value.
+//    StringToDouble("-123.45") -> -123.45.
+//    StringToDouble("--123.45") -> NaN  // junk_string_value.
+//    StringToDouble("123e45") -> 123e45.
+//    StringToDouble("123E45") -> 123e45.
+//    StringToDouble("123e+45") -> 123e45.
+//    StringToDouble("123E-45") -> 123e-45.
+//    StringToDouble("123e") -> 123.0  // trailing junk ignored.
+//    StringToDouble("123e-") -> 123.0  // trailing junk ignored.
+//    StringToDouble("+NaN") -> NaN  // NaN string literal.
+//    StringToDouble("-infinity") -> -inf.  // infinity literal.
+//    StringToDouble("Infinity") -> NaN  // junk_string_value.
+//
+//  flags = ALLOW_OCTAL | ALLOW_LEADING_SPACES,
+//  empty_string_value = 0.0,
+//  junk_string_value = NaN,
+//  infinity_symbol = NULL,
+//  nan_symbol = NULL:
+//    StringToDouble("0x1234") -> NaN  // junk_string_value.
+//    StringToDouble("01234") -> 668.0.
+//    StringToDouble("") -> 0.0  // empty_string_value.
+//    StringToDouble(" ") -> 0.0  // empty_string_value.
+//    StringToDouble(" 1") -> 1.0
+//    StringToDouble("0x") -> NaN  // junk_string_value.
+//    StringToDouble("0123e45") -> NaN  // junk_string_value.
+//    StringToDouble("01239E45") -> 1239e45.
+//    StringToDouble("-infinity") -> NaN  // junk_string_value.
+//    StringToDouble("NaN") -> NaN  // junk_string_value.
+StringToDoubleConverter(int flags,
+double empty_string_value,
+double junk_string_value,
+const char* infinity_symbol,
+const char* nan_symbol)
+: flags_(flags),
+empty_string_value_(empty_string_value),
+junk_string_value_(junk_string_value),
+infinity_symbol_(infinity_symbol),
+nan_symbol_(nan_symbol) {
+}
+// Performs the conversion.
+// The output parameter 'processed_characters_count' is set to the number
+// of characters that have been processed to read the number.
+// Spaces than are processed with ALLOW_{LEADING|TRAILING}_SPACES are included
+// in the 'processed_characters_count'. Trailing junk is never included.
+double StringToDouble(const char* buffer,
+int length,
+int* processed_characters_count) const {
+return StringToIeee(buffer, length, processed_characters_count, true);
+}
+// Same as StringToDouble but reads a float.
+// Note that this is not equivalent to static_cast<float>(StringToDouble(...))
+// due to potential double-rounding.
+float StringToFloat(const char* buffer,
+int length,
+int* processed_characters_count) const {
+return static_cast<float>(StringToIeee(buffer, length,
+processed_characters_count, false));
+}
+private:
+const int flags_;
+const double empty_string_value_;
+const double junk_string_value_;
+const char* const infinity_symbol_;
+const char* const nan_symbol_;
+double StringToIeee(const char* buffer,
+int length,
+int* processed_characters_count,
+bool read_as_double) const;
+DISALLOW_IMPLICIT_CONSTRUCTORS(StringToDoubleConverter);
+};
+}  // namespace double_conversion
+#endif  // DOUBLE_CONVERSION_DOUBLE_CONVERSION_H_

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mfbt/double-conversion/double-conversion.h