durationimpl.java

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     * 
     * @return New <code>Duration</code> that is <code>factor</code>times longer than this <code>Duration</code>.
     * 
     * @see #multiply(BigDecimal)
     */
    public Duration multiply(int factor) {
        return multiply(BigDecimal.valueOf(factor));
    }
    
    /**
     * Computes a new duration whose value is <code>factor</code> times
     * longer than the value of this duration.
     * 
     * <p>
     * For example,
     * <pre>
     * "P1M" (1 month) * "12" = "P12M" (12 months)
     * "PT1M" (1 min) * "0.3" = "PT18S" (18 seconds)
     * "P1M" (1 month) * "1.5" = IllegalStateException
     * </pre>
     *  
     * <p>
     * Since the {@link Duration} class is immutable, this method
     * doesn't change the value of this object. It simply computes
     * a new Duration object and returns it.
     * 
     * <p>
     * The operation will be performed field by field with the precision
     * of {@link BigDecimal}. Since all the fields except seconds are
     * restricted to hold integers,
     * any fraction produced by the computation will be
     * carried down toward the next lower unit. For example,
     * if you multiply "P1D" (1 day) with "0.5", then it will be 0.5 day,
     * which will be carried down to "PT12H" (12 hours).
     * When fractions of month cannot be meaningfully carried down
     * to days, or year to months, this will cause an
     * {@link IllegalStateException} to be thrown. 
     * For example if you multiple one month by 0.5.</p>
     * 
     * <p>
     * To avoid {@link IllegalStateException}, use
     * the {@link #normalizeWith(Calendar)} method to remove the years
     * and months fields.
     * 
     * @param factor to multiply by
     * 
     * @return
     *      returns a non-null valid {@link Duration} object
     *
     * @throws IllegalStateException if operation produces fraction in 
     * the months field.
     *
     * @throws NullPointerException if the <code>factor</code> parameter is 
     * <code>null</code>.
     *
     */
    public Duration multiply(BigDecimal factor) {
        BigDecimal carry = ZERO;
        int factorSign = factor.signum();
        factor = factor.abs();
        
        BigDecimal[] buf = new BigDecimal[6];
        
        for (int i = 0; i < 5; i++) {
            BigDecimal bd = getFieldAsBigDecimal(FIELDS[i]);
            bd = bd.multiply(factor).add(carry);
            
            buf[i] = bd.setScale(0, BigDecimal.ROUND_DOWN);
            
            bd = bd.subtract(buf[i]);
            if (i == 1) {
                if (bd.signum() != 0) {
                    throw new IllegalStateException(); // illegal carry-down
                } else {
                    carry = ZERO;
                }
            } else {
                carry = bd.multiply(FACTORS[i]);
            }
        }
        
        if (seconds != null) {
            buf[5] = seconds.multiply(factor).add(carry);
        } else {
            buf[5] = carry;
        }
                
        return new DurationImpl(
            this.signum * factorSign >= 0,
            toBigInteger(buf[0], null == years),
            toBigInteger(buf[1], null == months),
            toBigInteger(buf[2], null == days),
            toBigInteger(buf[3], null == hours),
            toBigInteger(buf[4], null == minutes),
            (buf[5].signum() == 0 && seconds == null) ? null : buf[5]);
    }
    
    /**
     * <p>Gets the value of the field as a {@link BigDecimal}.</p>
     * 
     * <p>If the field is unset, return 0.</p>
     * 
     * @param f Field to get value for.
     * 
     * @return  non-null valid {@link BigDecimal}.
     */
    private BigDecimal getFieldAsBigDecimal(DatatypeConstants.Field f) {
        if (f == DatatypeConstants.SECONDS) {
            if (seconds != null) {
                return seconds;
            } else {
                return ZERO;
            }
        } else {
            BigInteger bi = (BigInteger) getField(f);
            if (bi == null) {
                return ZERO;
            } else {
                return new BigDecimal(bi);
            }
        }
    }
    
    /**
     * <p>BigInteger value of BigDecimal value.</p>
     * 
     * @param value Value to convert.
     * @param canBeNull Can returned value be null?
     * 
     * @return BigInteger value of BigDecimal, possibly null.
     */
    private static BigInteger toBigInteger(
        BigDecimal value,
        boolean canBeNull) {
        if (canBeNull && value.signum() == 0) {
            return null;
        } else {
            return value.unscaledValue();
        }
    }
    
    /**
     * 1 unit of FIELDS[i] is equivalent to <code>FACTORS[i]</code> unit of
     * FIELDS[i+1].
     */
    private static final BigDecimal[] FACTORS = new BigDecimal[]{
        BigDecimal.valueOf(12),
        null/*undefined*/,
        BigDecimal.valueOf(24),
        BigDecimal.valueOf(60),
        BigDecimal.valueOf(60)
    };    
    
    /**
     * <p>Computes a new duration whose value is <code>this+rhs</code>.</p>
     * 
     * <p>For example,</p>
     * <pre>
     * "1 day" + "-3 days" = "-2 days"
     * "1 year" + "1 day" = "1 year and 1 day"
     * "-(1 hour,50 minutes)" + "-20 minutes" = "-(1 hours,70 minutes)"
     * "15 hours" + "-3 days" = "-(2 days,9 hours)"
     * "1 year" + "-1 day" = IllegalStateException
     * </pre>
     * 
     * <p>Since there's no way to meaningfully subtract 1 day from 1 month,
     * there are cases where the operation fails in
     * {@link IllegalStateException}.</p> 
     * 
     * <p>
     * Formally, the computation is defined as follows.</p>
     * <p>
     * Firstly, we can assume that two {@link Duration}s to be added
     * are both positive without losing generality (i.e.,
     * <code>(-X)+Y=Y-X</code>, <code>X+(-Y)=X-Y</code>,
     * <code>(-X)+(-Y)=-(X+Y)</code>)
     * 
     * <p>
     * Addition of two positive {@link Duration}s are simply defined as  
     * field by field addition where missing fields are treated as 0.
     * <p>
     * A field of the resulting {@link Duration} will be unset if and
     * only if respective fields of two input {@link Duration}s are unset. 
     * <p>
     * Note that <code>lhs.add(rhs)</code> will be always successful if
     * <code>lhs.signum()*rhs.signum()!=-1</code> or both of them are
     * normalized.</p>
     * 
     * @param rhs <code>Duration</code> to add to this <code>Duration</code>
     * 
     * @return
     *      non-null valid Duration object.
     * 
     * @throws NullPointerException
     *      If the rhs parameter is null.
     * @throws IllegalStateException
     *      If two durations cannot be meaningfully added. For
     *      example, adding negative one day to one month causes
     *      this exception.
     * 
     * 
     * @see #subtract(Duration)
     */
    public Duration add(final Duration rhs) {
        Duration lhs = this;
        BigDecimal[] buf = new BigDecimal[6];
        
        buf[0] = sanitize((BigInteger) lhs.getField(DatatypeConstants.YEARS),
        	lhs.getSign()).add(sanitize((BigInteger) rhs.getField(DatatypeConstants.YEARS),  rhs.getSign()));
        buf[1] = sanitize((BigInteger) lhs.getField(DatatypeConstants.MONTHS),
        	lhs.getSign()).add(sanitize((BigInteger) rhs.getField(DatatypeConstants.MONTHS), rhs.getSign()));
        buf[2] = sanitize((BigInteger) lhs.getField(DatatypeConstants.DAYS),
        	lhs.getSign()).add(sanitize((BigInteger) rhs.getField(DatatypeConstants.DAYS),   rhs.getSign()));
        buf[3] = sanitize((BigInteger) lhs.getField(DatatypeConstants.HOURS),
        	lhs.getSign()).add(sanitize((BigInteger) rhs.getField(DatatypeConstants.HOURS),  rhs.getSign()));
        buf[4] = sanitize((BigInteger) lhs.getField(DatatypeConstants.MINUTES),
        	lhs.getSign()).add(sanitize((BigInteger) rhs.getField(DatatypeConstants.MINUTES), rhs.getSign()));
        buf[5] = sanitize((BigDecimal) lhs.getField(DatatypeConstants.SECONDS),
        	lhs.getSign()).add(sanitize((BigDecimal) rhs.getField(DatatypeConstants.SECONDS), rhs.getSign()));
        
        // align sign
        alignSigns(buf, 0, 2); // Y,M
        alignSigns(buf, 2, 6); // D,h,m,s
        
        // make sure that the sign bit is consistent across all 6 fields.
        int s = 0;
        for (int i = 0; i < 6; i++) {
            if (s * buf[i].signum() < 0) {
                throw new IllegalStateException();
            }
            if (s == 0) {
                s = buf[i].signum();
            }
        }
        
        return new DurationImpl(
            s >= 0,
            toBigInteger(sanitize(buf[0], s),
            	lhs.getField(DatatypeConstants.YEARS) == null && rhs.getField(DatatypeConstants.YEARS) == null),
            toBigInteger(sanitize(buf[1], s),
            	lhs.getField(DatatypeConstants.MONTHS) == null && rhs.getField(DatatypeConstants.MONTHS) == null),
            toBigInteger(sanitize(buf[2], s),
            	lhs.getField(DatatypeConstants.DAYS) == null && rhs.getField(DatatypeConstants.DAYS) == null),
            toBigInteger(sanitize(buf[3], s),
            	lhs.getField(DatatypeConstants.HOURS) == null && rhs.getField(DatatypeConstants.HOURS) == null),
            toBigInteger(sanitize(buf[4], s),
            	lhs.getField(DatatypeConstants.MINUTES) == null && rhs.getField(DatatypeConstants.MINUTES) == null),
             (buf[5].signum() == 0
             && lhs.getField(DatatypeConstants.SECONDS) == null
             && rhs.getField(DatatypeConstants.SECONDS) == null) ? null : sanitize(buf[5], s));
    }
    
    private static void alignSigns(BigDecimal[] buf, int start, int end) {
        // align sign
        boolean touched;
        
        do { // repeat until all the sign bits become consistent
            touched = false;
            int s = 0; // sign of the left fields

            for (int i = start; i < end; i++) {
                if (s * buf[i].signum() < 0) {
                    // this field has different sign than its left field.
                    touched = true;

                    // compute the number of unit that needs to be borrowed.
                    BigDecimal borrow =
                        buf[i].abs().divide(
                            FACTORS[i - 1],
                            BigDecimal.ROUND_UP);
                    if (buf[i].signum() > 0) {
                        borrow = borrow.negate();
                    }

                    // update values
                    buf[i - 1] = buf[i - 1].subtract(borrow);
                    buf[i] = buf[i].add(borrow.multiply(FACTORS[i - 1]));
                }
                if (buf[i].signum() != 0) {
                    s = buf[i].signum();
                }
            }
        } while (touched);
    }
    
    /**
     * Compute <code>value*signum</code> where value==null is treated as
     * value==0.
     * @param value Value to sanitize.
     * @param signum 0 to sanitize to 0, > 0 to sanitize to <code>value</code>, < 0 to sanitize to negative <code>value</code>.
     *
     * @return non-null {@link BigDecimal}.
     */
    private static BigDecimal sanitize(BigInteger value, int signum) {
        if (signum == 0 || value == null) {
            return ZERO;
        }
        if (signum > 0) {
            return new BigDecimal(value);
        }
        return new BigDecimal(value.negate());
    }
        
    /**
     * <p>Compute <code>value*signum</code> where <code>value==null</code> is treated as <code>value==0</code></p>.
     * 
     * @param value Value to sanitize.
     * @param signum 0 to sanitize to 0, > 0 to sanitize to <code>value</code>, < 0 to sanitize to negative <code>value</code>.
     * 
     * @return non-null {@link BigDecimal}.
     */
    static BigDecimal sanitize(BigDecimal value, int signum) {
        if (signum == 0 || value == null) {
            return ZERO;
        }
        if (signum > 0) {
            return value;
        }
        return value.negate();
    }
    
    /**
     * <p>Computes a new duration whose value is <code>this-rhs</code>.</p>
     * 
     * <p>For example:</p>
     * <pre>
     * "1 day" - "-3 days" = "4 days"
     * "1 year" - "1 day" = IllegalStateException
     * "-(1 hour,50 minutes)" - "-20 minutes" = "-(1hours,30 minutes)"
     * "15 hours" - "-3 days" = "3 days and 15 hours"
     * "1 year" - "-1 day" = "1 year and 1 day"
     * </pre>
     * 
     * <p>Since there's no way to meaningfully subtract 1 day from 1 month,
     * there are cases where the operation fails in {@link IllegalStateException}.</p> 
     * 
     * <p>Formally the computation is defined as follows.
     * First, we can assume that two {@link Duration}s are both positive
     * without losing generality.  (i.e.,
     * <code>(-X)-Y=-(X+Y)</code>, <code>X-(-Y)=X+Y</code>,
     * <code>(-X)-(-Y)=-(X-Y)</code>)</p>
     *  
     * <p>Then two durations are subtracted field by field.
     * If the sign of any non-zero field <tt>F</tt> is different from
     * the sign of the most significant field,
     * 1 (if <tt>F</tt> is negative) or -1 (otherwise)
     * will be borrowed from the next bigger unit of <tt>F</tt>.</p>
     * 
     * <p>This process is repeated until all the non-zero fields have
     * the same sign.</p> 
     * 
     * <p>If a borrow occurs in the days field (in other words, if
     * the computation needs to borrow 1 or -1 month to compensate
     * days), then the computation fails by throwing an
     * {@link IllegalStateException}.</p>
     * 
     * @param rhs <code>Duration</code> to substract from this <code>Duration</code>.
     *  
     * @return New <code>Duration</code> created from subtracting <code>rhs</code> from this <code>Duration</code>.
     * 
     * @throws IllegalStateException
     *      If two dur