/**
* 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;
}
/**
* Extracts the significant digits in the decimal representation of the argument. A decimal point
* may be optionally inserted in the string of digits (as long as its position lies within the
* extracted digits - if not, the caller must prepend or append the appropriate zeroes and decimal
* point).
*
* @param insertDecimalPoint the insert decimal point
* @param magnitude the magnitude
* @return the string containing the significant digits and possibly a decimal point
*/
private String extractSignificantDigits(final boolean insertDecimalPoint, final int[] magnitude) {
WB_DoubleDouble y = this.abs();
// compute *correct* magnitude of y
int mag = magnitude(y.hi);
final WB_DoubleDouble scale = TEN.pow(mag);
y = y.divide(scale);
// fix magnitude if off by one
if (y.gt(TEN)) {
y = y.divide(TEN);
mag += 1;
} else if (y.lt(ONE)) {
y = y.multiply(TEN);
mag -= 1;
}
final int decimalPointPos = mag + 1;
final StringBuffer buf = new StringBuffer();
final int numDigits = MAX_PRINT_DIGITS - 1;
for (int i = 0; i <= numDigits; i++) {
if (insertDecimalPoint && (i == decimalPointPos)) {
buf.append('.');
}
final int digit = (int) y.hi;
// System.out.println("printDump: [" + i + "] digit: " + digit +
// " y: " + y.dump() + " buf: " + buf);
/** This should never happen, due to heuristic checks on remainder below */
if ((digit < 0) || (digit > 9)) {
// System.out.println("digit > 10 : " + digit);
// throw new
// IllegalStateException("Internal errror: found digit = " +
// digit);
}
/**
* If a negative remainder is encountered, simply terminate the extraction. This is robust,
* but maybe slightly inaccurate. My current hypothesis is that negative remainders only occur
* for very small lo components, so the inaccuracy is tolerable
*/
if (digit < 0) {
break;
// throw new
// IllegalStateException("Internal errror: found digit = " +
// digit);
}
boolean rebiasBy10 = false;
char digitChar = 0;
if (digit > 9) {
// set flag to re-bias after next 10-shift
rebiasBy10 = true;
// output digit will end up being '9'
digitChar = '9';
} else {
digitChar = (char) ('0' + digit);
}
buf.append(digitChar);
y = (y.subtract(WB_DoubleDouble.valueOf(digit)).multiply(TEN));
if (rebiasBy10) {
y.selfAdd(TEN);
}
boolean continueExtractingDigits = true;
/**
* Heuristic check: if the remaining portion of y is non-positive, assume that output is
* complete
*/
// if (y.hi <= 0.0)
// if (y.hi < 0.0)
// continueExtractingDigits = false;
/**
* Check if remaining digits will be 0, and if so don't output them. Do this by comparing the
* magnitude of the remainder with the expected precision.
*/
final int remMag = magnitude(y.hi);
if ((remMag < 0) && (Math.abs(remMag) >= (numDigits - i))) {
continueExtractingDigits = false;
}
if (!continueExtractingDigits) {
break;
}
}
magnitude[0] = mag;
return buf.toString();
}
