Source/WTF/wtf/DecimalNumber.cpp

/*
 * Copyright (C) 2010 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. 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.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``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 APPLE INC. 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. 
 */

#include "config.h"
#include "DecimalNumber.h"
#include <math.h>
#include <wtf/MathExtras.h>
#include <wtf/text/WTFString.h>

namespace WTF {

unsigned DecimalNumber::bufferLengthForStringDecimal() const
{
    unsigned length = 0;
    // if the exponent is negative the number decimal representation is of the form:
    // [<sign>]0.[<zeros>]<significand>
    if (m_exponent < 0) {
        if (m_sign)
            ++length;
        length += 2; // for "0."
        length += -m_exponent - 1;
        length += m_precision;
        return length;
    }

    unsigned digitsBeforeDecimalPoint = m_exponent + 1;

    // If the precision is <= than the number of digits to get up to the decimal
    // point, then there is no fractional part, number is of the form:
    // [<sign>]<significand>[<zeros>]
    if (m_precision <= digitsBeforeDecimalPoint) {
        if (m_sign)
            ++length;
        length += m_precision;
        length += digitsBeforeDecimalPoint - m_precision;
        return length;
    }

    // If we get here, number starts before the decimal point, and ends after it,
    // as such is of the form:
    // [<sign>]<significand-begin>.<significand-end>
    if (m_sign)
        ++length;
    length += digitsBeforeDecimalPoint;
    ++length; // for decimal point
    length += m_precision - digitsBeforeDecimalPoint;

    return length;
}

unsigned DecimalNumber::bufferLengthForStringExponential() const
{
    unsigned length = 0;
    if (m_sign)
        ++length;

    // Add the significand
    ++length;

    if (m_precision > 1) {
        ++length; // for decimal point
        length += m_precision - 1;
    }

    // Add "e+" or "e-"
    length += 2;

    int exponent = (m_exponent >= 0) ? m_exponent : -m_exponent;

    // Add the exponent
    if (exponent >= 100)
        ++length;
    if (exponent >= 10)
        ++length;
    ++length;

    return length;
}

unsigned DecimalNumber::toStringDecimal(LChar* buffer, unsigned bufferLength) const
{
    ASSERT_UNUSED(bufferLength, bufferLength >= bufferLengthForStringDecimal());

    // Should always be at least one digit to add to the string!
    ASSERT(m_precision);
    LChar* next = buffer;

    // if the exponent is negative the number decimal representation is of the form:
    // [<sign>]0.[<zeros>]<significand>
    if (m_exponent < 0) {
        unsigned zeros = -m_exponent - 1;

        if (m_sign)
            *next++ = '-';
        *next++ = '0';
        *next++ = '.';
        for (unsigned i = 0; i < zeros; ++i)
            *next++ = '0';
        for (unsigned i = 0; i < m_precision; ++i)
            *next++ = m_significand[i];

        return next - buffer;
    }

    unsigned digitsBeforeDecimalPoint = m_exponent + 1;

    // If the precision is <= than the number of digits to get up to the decimal
    // point, then there is no fractional part, number is of the form:
    // [<sign>]<significand>[<zeros>]
    if (m_precision <= digitsBeforeDecimalPoint) {
        if (m_sign)
            *next++ = '-';
        for (unsigned i = 0; i < m_precision; ++i)
            *next++ = m_significand[i];
        for (unsigned i = 0; i < (digitsBeforeDecimalPoint - m_precision); ++i)
            *next++ = '0';

        return next - buffer;
    }

    // If we get here, number starts before the decimal point, and ends after it,
    // as such is of the form:
    // [<sign>]<significand-begin>.<significand-end>

    if (m_sign)
        *next++ = '-';
    for (unsigned i = 0; i < digitsBeforeDecimalPoint; ++i)
        *next++ = m_significand[i];
    *next++ = '.';
    for (unsigned i = digitsBeforeDecimalPoint; i < m_precision; ++i)
        *next++ = m_significand[i];

    return next - buffer;
}

unsigned DecimalNumber::toStringExponential(LChar* buffer, unsigned bufferLength) const
{
    ASSERT_UNUSED(bufferLength, bufferLength >= bufferLengthForStringExponential());

    // Should always be at least one digit to add to the string!
    ASSERT(m_precision);
    LChar* next = buffer;

    // Add the sign
    if (m_sign)
        *next++ = '-';

    // Add the significand
    *next++ = m_significand[0];
    if (m_precision > 1) {
        *next++ = '.';
        for (unsigned i = 1; i < m_precision; ++i)
            *next++ = m_significand[i];
    }

    // Add "e+" or "e-"
    *next++ = 'e';
    int exponent;
    if (m_exponent >= 0) {
        *next++ = '+';
        exponent = m_exponent;
    } else {
        *next++ = '-';
        exponent = -m_exponent;
    }

    // Add the exponent
    if (exponent >= 100)
        *next++ = '0' + exponent / 100;
    if (exponent >= 10)
        *next++ = '0' + (exponent % 100) / 10;
    *next++ = '0' + exponent % 10;

    return next - buffer;
}

} // namespace WTF