/**
* Computes a new DoubleDouble object whose value is <tt>(this - y)</tt>.
*
* @param y the subtrahend
* @return <tt>(this - y)</tt>
*/
public WB_DoubleDouble subtract(final WB_DoubleDouble y) {
return add(y.negate());
}
/**
* Converts a string representation of a real number into a DoubleDouble value. The format
* accepted is similar to the standard Java real number syntax. It is defined by the following
* regular expression:
*
* <pre>
* [<tt>+</tt>|<tt>-</tt>] {<i>digit</i>} [ <tt>.</tt> {<i>digit</i>} ] [ ( <tt>e</tt> | <tt>E</tt> ) [<tt>+</tt>|<tt>-</tt>
* ] {<i>digit</i>}+
*
* </pre>
*
* @param str the string to parse
* @return the value of the parsed number
* @throws NumberFormatException if <tt>str</tt> is not a valid representation of a number
*/
public static WB_DoubleDouble parse(final String str) throws NumberFormatException {
int i = 0;
final int strlen = str.length();
// skip leading whitespace
while (Character.isWhitespace(str.charAt(i))) {
i++;
}
// check for sign
boolean isNegative = false;
if (i < strlen) {
final char signCh = str.charAt(i);
if ((signCh == '-') || (signCh == '+')) {
i++;
if (signCh == '-') {
isNegative = true;
}
}
}
// scan all digits and accumulate into an integral value
// Keep track of the location of the decimal point (if any) to allow
// scaling later
final WB_DoubleDouble val = new WB_DoubleDouble();
int numDigits = 0;
int numBeforeDec = 0;
int exp = 0;
while (true) {
if (i >= strlen) {
break;
}
final char ch = str.charAt(i);
i++;
if (Character.isDigit(ch)) {
final double d = ch - '0';
val.selfMultiply(TEN);
// MD: need to optimize this
val.selfAdd(d);
numDigits++;
continue;
}
if (ch == '.') {
numBeforeDec = numDigits;
continue;
}
if ((ch == 'e') || (ch == 'E')) {
final String expStr = str.substring(i);
// this should catch any format problems with the exponent
try {
exp = Integer.parseInt(expStr);
} catch (final NumberFormatException ex) {
throw new NumberFormatException("Invalid exponent " + expStr + " in string " + str);
}
break;
}
throw new NumberFormatException(
"Unexpected character '" + ch + "' at position " + i + " in string " + str);
}
WB_DoubleDouble val2 = val;
// scale the number correctly
final int numDecPlaces = numDigits - numBeforeDec - exp;
if (numDecPlaces == 0) {
val2 = val;
} else if (numDecPlaces > 0) {
final WB_DoubleDouble scale = TEN.pow(numDecPlaces);
val2 = val.divide(scale);
} else if (numDecPlaces < 0) {
final WB_DoubleDouble scale = TEN.pow(-numDecPlaces);
val2 = val.multiply(scale);
}
// apply leading sign, if any
if (isNegative) {
return val2.negate();
}
return val2;
}