digitlist.java

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            // is more than the maximum fraction digits, then we have an underflow
            // for the printed representation.
            if (-decimalAt > maximumDigits) {
                // Handle an underflow to zero when we round something like
                // 0.0009 to 2 fractional digits.
                count = 0;
                return;
            } else if (-decimalAt == maximumDigits) {
                // If we round 0.0009 to 3 fractional digits, then we have to
                // create a new one digit in the least significant location.
                if (shouldRoundUp(0)) {
                    count = 1;
                    ++decimalAt;
                    digits[0] = '1';
                } else {
                    count = 0;
                }
                return;
            }
            // else fall through
        }

        // Eliminate trailing zeros.
        while (count > 1 && digits[count - 1] == '0')
            --count;

        // Eliminate digits beyond maximum digits to be displayed.
        // Round up if appropriate.
        round(fixedPoint ? (maximumDigits + decimalAt) : maximumDigits);
    }

    /**
     * Round the representation to the given number of digits.
     * @param maximumDigits The maximum number of digits to be shown.
     * Upon return, count will be less than or equal to maximumDigits.
     */
    private final void round(int maximumDigits)
    {
        // Eliminate digits beyond maximum digits to be displayed.
        // Round up if appropriate.
        if (maximumDigits >= 0 && maximumDigits < count)
        {
            if (shouldRoundUp(maximumDigits)) {
                // Rounding up involved incrementing digits from LSD to MSD.
                // In most cases this is simple, but in a worst case situation
                // (9999..99) we have to adjust the decimalAt value.
                for (;;)
                {
                    --maximumDigits;
                    if (maximumDigits < 0)
                    {
                        // We have all 9's, so we increment to a single digit
                        // of one and adjust the exponent.
                        digits[0] = '1';
                        ++decimalAt;
                        maximumDigits = 0; // Adjust the count
                        break;
                    }

                    ++digits[maximumDigits];
                    if (digits[maximumDigits] <= '9') break;
                    // digits[maximumDigits] = '0'; // Unnecessary since we'll truncate this
                }
                ++maximumDigits; // Increment for use as count
            }
            count = maximumDigits;

            // Eliminate trailing zeros.
            while (count > 1 && digits[count-1] == '0') {
                --count;
            }
        }
    }


    /**
     * Return true if truncating the representation to the given number
     * of digits will result in an increment to the last digit.  This
     * method implements half-even rounding, the default rounding mode.
     * [bnf]
     * @param maximumDigits the number of digits to keep, from 0 to
     * <code>count-1</code>.  If 0, then all digits are rounded away, and
     * this method returns true if a one should be generated (e.g., formatting
     * 0.09 with "#.#").
     * @return true if digit <code>maximumDigits-1</code> should be
     * incremented
     */
    private boolean shouldRoundUp(int maximumDigits) {
        boolean increment = false;
        // Implement IEEE half-even rounding
        if (maximumDigits < count) {
            if (digits[maximumDigits] > '5') {
                return true;
            } else if (digits[maximumDigits] == '5' ) {
                for (int i=maximumDigits+1; i<count; ++i) {
                    if (digits[i] != '0') {
                        return true;
                    }
                }
                return maximumDigits > 0 && (digits[maximumDigits-1] % 2 != 0);
            }
	}
        return false;
    }

    /**
     * Utility routine to set the value of the digit list from a long
     */
    public final void set(long source)
    {
        set(source, 0);
    }

    /**
     * Set the digit list to a representation of the given long value.
     * @param source Value to be converted; must be >= 0 or ==
     * Long.MIN_VALUE.
     * @param maximumDigits The most digits which should be converted.
     * If maximumDigits is lower than the number of significant digits
     * in source, the representation will be rounded.  Ignored if <= 0.
     */
    public final void set(long source, int maximumDigits)
    {
        // This method does not expect a negative number. However,
        // "source" can be a Long.MIN_VALUE (-9223372036854775808),
        // if the number being formatted is a Long.MIN_VALUE.  In that
        // case, it will be formatted as -Long.MIN_VALUE, a number
        // which is outside the legal range of a long, but which can
        // be represented by DigitList.
        if (source <= 0) {
            if (source == Long.MIN_VALUE) {
                decimalAt = count = MAX_COUNT;
                System.arraycopy(LONG_MIN_REP, 0, digits, 0, count);
            } else {
                decimalAt = count = 0; // Values <= 0 format as zero
            }
        } else {
            // Rewritten to improve performance.  I used to call
            // Long.toString(), which was about 4x slower than this code.
            int left = MAX_COUNT;
            int right;
            while (source > 0) {
                digits[--left] = (char)('0' + (source % 10));
                source /= 10;
            }
            decimalAt = MAX_COUNT - left;
            // Don't copy trailing zeros.  We are guaranteed that there is at
            // least one non-zero digit, so we don't have to check lower bounds.
            for (right = MAX_COUNT - 1; digits[right] == '0'; --right)
		;
            count = right - left + 1;
            System.arraycopy(digits, left, digits, 0, count);
        }        
        if (maximumDigits > 0) round(maximumDigits);
    }

    /**
     * equality test between two digit lists.
     */
    public boolean equals(Object obj) {
        if (this == obj)                      // quick check
            return true;
        if (!(obj instanceof DigitList))         // (1) same object?
            return false;
        DigitList other = (DigitList) obj;
        if (count != other.count ||
        decimalAt != other.decimalAt)
            return false;
        for (int i = 0; i < count; i++)
            if (digits[i] != other.digits[i])
                return false;
        return true;
    }

    /**
     * Generates the hash code for the digit list.
     */
    public int hashCode() {
        int hashcode = decimalAt;

        for (int i = 0; i < count; i++)
            hashcode = hashcode * 37 + digits[i];

        return hashcode;
    }

    /**
     * Creates a copy of this object.
     * @return a clone of this instance.
     */
    public Object clone() {
	try {
	    DigitList other = (DigitList) super.clone();
	    char[] newDigits = new char[digits.length];
	    System.arraycopy(digits, 0, newDigits, 0, digits.length);
	    other.digits = newDigits;
	    return other;
	} catch (CloneNotSupportedException e) {
	    throw new InternalError();
	}
    }

    /**
     * Returns true if this DigitList represents Long.MIN_VALUE;
     * false, otherwise.  This is required so that getLong() works.
     */
    private boolean isLongMIN_VALUE()
    {
        if (decimalAt != count || count != MAX_COUNT)
            return false;

	for (int i = 0; i < count; ++i)
        {
            if (digits[i] != LONG_MIN_REP[i]) return false;
        }

        return true;
    }

    private static final int parseInt(char[] str, int offset) {
	char c;
	boolean positive = true;
	if ((c = str[offset]) == '-') {
	    positive = false;
	    offset++;
	} else if (c == '+') {
	    offset++;
	}

	int value = 0;
	while (offset < str.length) {
	    c = str[offset++];
	    if (c >= '0' && c <= '9') {
		value = value * 10 + (c - '0');
	    } else {
		break;
	    }
	}
	return positive ? value : -value;
    }

    // The digit part of -9223372036854775808L
    private static final char[] LONG_MIN_REP = "9223372036854775808".toCharArray();

    public String toString()
    {
        if (isZero()) return "0";
        StringBuffer buf = getStringBuffer();
	buf.append("0.").append(digits, 0, count);
        buf.append("x10^");
        buf.append(decimalAt);
        return buf.toString();
    }

    private StringBuffer tempBuffer;

    private StringBuffer getStringBuffer() {
	if (tempBuffer == null) {
	    tempBuffer = new StringBuffer(MAX_COUNT);
	} else {
	    tempBuffer.setLength(0);
	}
	return tempBuffer;
    }
}