third_party/WebKit/Source/wtf/dtoa.cpp

/****************************************************************
 *
 * The author of this software is David M. Gay.
 *
 * Copyright (c) 1991, 2000, 2001 by Lucent Technologies.
 * Copyright (C) 2002, 2005, 2006, 2007, 2008, 2010, 2012 Apple Inc.
 * All rights reserved.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose without fee is hereby granted, provided that this entire notice
 * is included in all copies of any software which is or includes a copy
 * or modification of this software and in all copies of the supporting
 * documentation for such software.
 *
 * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTY.  IN PARTICULAR, NEITHER THE AUTHOR NOR LUCENT MAKES ANY
 * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
 * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
 *
 ***************************************************************/

/* Please send bug reports to David M. Gay (dmg at acm dot org,
 * with " at " changed at "@" and " dot " changed to ".").    */

/* On a machine with IEEE extended-precision registers, it is
 * necessary to specify double-precision (53-bit) rounding precision
 * before invoking strtod or dtoa.  If the machine uses (the equivalent
 * of) Intel 80x87 arithmetic, the call
 *    _control87(PC_53, MCW_PC);
 * does this with many compilers.  Whether this or another call is
 * appropriate depends on the compiler; for this to work, it may be
 * necessary to #include "float.h" or another system-dependent header
 * file.
 */

#include "wtf/dtoa.h"

#include "wtf/Vector.h"
#include <string.h>

namespace WTF {

const char* numberToString(double d, NumberToStringBuffer buffer) {
  double_conversion::StringBuilder builder(buffer, NumberToStringBufferLength);
  const double_conversion::DoubleToStringConverter& converter =
      double_conversion::DoubleToStringConverter::EcmaScriptConverter();
  converter.ToShortest(d, &builder);
  return builder.Finalize();
}

static inline const char* formatStringTruncatingTrailingZerosIfNeeded(
    NumberToStringBuffer buffer,
    double_conversion::StringBuilder& builder) {
  size_t length = builder.position();

  // If there is an exponent, stripping trailing zeros would be incorrect.
  // FIXME: Zeros should be stripped before the 'e'.
  if (memchr(buffer, 'e', length))
    return builder.Finalize();

  size_t decimalPointPosition = 0;
  for (; decimalPointPosition < length; ++decimalPointPosition) {
    if (buffer[decimalPointPosition] == '.')
      break;
  }

  // No decimal seperator found, early exit.
  if (decimalPointPosition == length)
    return builder.Finalize();

  size_t truncatedLength = length - 1;
  for (; truncatedLength > decimalPointPosition; --truncatedLength) {
    if (buffer[truncatedLength] != '0')
      break;
  }

  // No trailing zeros found to strip.
  if (truncatedLength == length - 1)
    return builder.Finalize();

  // If we removed all trailing zeros, remove the decimal point as well.
  if (truncatedLength == decimalPointPosition) {
    ASSERT(truncatedLength > 0);
    --truncatedLength;
  }

  // Truncate the StringBuilder, and return the final result.
  builder.SetPosition(truncatedLength + 1);
  return builder.Finalize();
}

const char* numberToFixedPrecisionString(double d,
                                         unsigned significantFigures,
                                         NumberToStringBuffer buffer) {
  // Mimic String::format("%.[precision]g", ...), but use dtoas rounding
  // facilities.
  // "g": Signed value printed in f or e format, whichever is more compact for
  // the given value and precision.
  // The e format is used only when the exponent of the value is less than -4 or
  // greater than or equal to the precision argument. Trailing zeros are
  // truncated, and the decimal point appears only if one or more digits follow
  // it.
  // "precision": The precision specifies the maximum number of significant
  // digits printed.
  double_conversion::StringBuilder builder(buffer, NumberToStringBufferLength);
  const double_conversion::DoubleToStringConverter& converter =
      double_conversion::DoubleToStringConverter::EcmaScriptConverter();
  converter.ToPrecision(d, significantFigures, &builder);
  // FIXME: Trailing zeros should never be added in the first place. The
  // current implementation does not strip when there is an exponent, eg.
  // 1.50000e+10.
  return formatStringTruncatingTrailingZerosIfNeeded(buffer, builder);
}

const char* numberToFixedWidthString(double d,
                                     unsigned decimalPlaces,
                                     NumberToStringBuffer buffer) {
  // Mimic String::format("%.[precision]f", ...), but use dtoas rounding
  // facilities.
  // "f": Signed value having the form [ - ]dddd.dddd, where dddd is one or more
  // decimal digits.  The number of digits before the decimal point depends on
  // the magnitude of the number, and the number of digits after the decimal
  // point depends on the requested precision.
  // "precision": The precision value specifies the number of digits after the
  // decimal point.  If a decimal point appears, at least one digit appears
  // before it.  The value is rounded to the appropriate number of digits.
  double_conversion::StringBuilder builder(buffer, NumberToStringBufferLength);
  const double_conversion::DoubleToStringConverter& converter =
      double_conversion::DoubleToStringConverter::EcmaScriptConverter();
  converter.ToFixed(d, decimalPlaces, &builder);
  return builder.Finalize();
}

namespace Internal {

double parseDoubleFromLongString(const UChar* string,
                                 size_t length,
                                 size_t& parsedLength) {
  Vector<LChar> conversionBuffer(length);
  for (size_t i = 0; i < length; ++i)
    conversionBuffer[i] = isASCII(string[i]) ? string[i] : 0;
  return parseDouble(conversionBuffer.data(), length, parsedLength);
}

}  // namespace Internal

}  // namespace WTF