/*
 * @(#)FloatingDecimal.java	1.17 00/02/02
 *
 * Copyright 1996-2000 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the proprietary information of Sun Microsystems, Inc.  
 * Use is subject to license terms.
 * 
 */

package java.lang;

class FloatingDecimal{
    boolean	isExceptional;
    boolean	isNegative;
    int		decExponent;
    char	digits[];
    int		nDigits;
    int		bigIntExp;
    int		bigIntNBits;
    boolean	mustSetRoundDir = false;
    int		roundDir; // set by doubleValue

    private	FloatingDecimal( boolean negSign, int decExponent, char []digits, int n,  boolean e )
    {
	isNegative = negSign;
	isExceptional = e;
	this.decExponent = decExponent;
	this.digits = digits;
	this.nDigits = n;
    }

    /*
     * Constants of the implementation
     * Most are IEEE-754 related.
     * (There are more really boring constants at the end.)
     */
    static final long	signMask = 0x8000000000000000L;
    static final long	expMask  = 0x7ff0000000000000L;
    static final long	fractMask= ~(signMask|expMask);
    static final int	expShift = 52;
    static final int	expBias  = 1023;
    static final long	fractHOB = ( 1L<<expShift ); // assumed High-Order bit
    static final long	expOne	 = ((long)expBias)<<expShift; // exponent of 1.0
    static final int	maxSmallBinExp = 62;
    static final int	minSmallBinExp = -( 63 / 3 );
    static final int	maxDecimalDigits = 15;
    static final int	maxDecimalExponent = 308;
    static final int	minDecimalExponent = -324;
    static final int	bigDecimalExponent = 324; // i.e. abs(minDecimalExponent)

    static final long	highbyte = 0xff00000000000000L;
    static final long	highbit  = 0x8000000000000000L;
    static final long	lowbytes = ~highbyte;

    static final int	singleSignMask =    0x80000000;
    static final int	singleExpMask  =    0x7f800000;
    static final int	singleFractMask =   ~(singleSignMask|singleExpMask);
    static final int	singleExpShift	=   23;
    static final int	singleFractHOB	=   1<<singleExpShift;
    static final int	singleExpBias	=   127;
    static final int	singleMaxDecimalDigits = 7;
    static final int	singleMaxDecimalExponent = 38;
    static final int	singleMinDecimalExponent = -45;

    static final int	intDecimalDigits = 9;


    /*
     * count number of bits from high-order 1 bit to low-order 1 bit,
     * inclusive.
     */
    private static int
    countBits( long v ){
	//
	// the strategy is to shift until we get a non-zero sign bit
	// then shift until we have no bits left, counting the difference.
	// we do byte shifting as a hack. Hope it helps.
	//
	if ( v == 0L ) return 0;

	while ( ( v & highbyte ) == 0L ){
	    v <<= 8;
	}
	while ( v > 0L ) { // i.e. while ((v&highbit) == 0L )
	    v <<= 1;
	}

	int n = 0;
	while (( v & lowbytes ) != 0L ){
	    v <<= 8;
	    n += 8;
	}
	while ( v != 0L ){
	    v <<= 1;
	    n += 1;
	}
	return n;
    }

    /*
     * Keep big powers of 5 handy for future reference.
     */
    private static FDBigInt b5p[];

    private static synchronized FDBigInt
    big5pow( int p ){
	if ( p < 0 )
	    throw new RuntimeException( "Assertion botch: negative power of 5");
	if ( b5p == null ){
	    b5p = new FDBigInt[ p+1 ];
	}else if (b5p.length <= p ){
	    FDBigInt t[] = new FDBigInt[ p+1 ];
	    System.arraycopy( b5p, 0, t, 0, b5p.length );
	    b5p = t;
	}
	if ( b5p[p] != null )
	    return b5p[p];
	else if ( p < small5pow.length )
	    return b5p[p] = new FDBigInt( small5pow[p] );
	else if ( p < long5pow.length )
	    return b5p[p] = new FDBigInt( long5pow[p] );
	else {
	    // construct the value.
	    // recursively.
	    int q, r;
	    // in order to compute 5^p,
	    // compute its square root, 5^(p/2) and square.
	    // or, let q = p / 2, r = p -q, then
	    // 5^p = 5^(q+r) = 5^q * 5^r
	    q = p >> 1;
	    r = p - q;
	    FDBigInt bigq =  b5p[q];
	    if ( bigq == null )
		bigq = big5pow ( q );
	    if ( r < small5pow.length ){
		return (b5p[p] = bigq.mult( small5pow[r] ) );
	    }else{
		FDBigInt bigr = b5p[ r ];
		if ( bigr == null )
		    bigr = big5pow( r );
		return (b5p[p] = bigq.mult( bigr ) );
	    }
	}
    }

    //
    // a common operation
    //
    private static FDBigInt
    multPow52( FDBigInt v, int p5, int p2 ){
	if ( p5 != 0 ){
	    if ( p5 < small5pow.length ){
		v = v.mult( small5pow[p5] );
	    } else {
		v = v.mult( big5pow( p5 ) );
	    }
	}
	if ( p2 != 0 ){
	    v.lshiftMe( p2 );
	}
	return v;
    }

    //
    // another common operation
    //
    private static FDBigInt
    constructPow52( int p5, int p2 ){
	FDBigInt v = new FDBigInt( big5pow( p5 ) );
	if ( p2 != 0 ){
	    v.lshiftMe( p2 );
	}
	return v;
    }

    /*
     * Make a floating double into a FDBigInt.
     * This could also be structured as a FDBigInt
     * constructor, but we'd have to build a lot of knowledge
     * about floating-point representation into it, and we don't want to.
     *
     * AS A SIDE EFFECT, THIS METHOD WILL SET THE INSTANCE VARIABLES
     * bigIntExp and bigIntNBits
     *
     */
    private FDBigInt
    doubleToBigInt( double dval ){
	long lbits = Double.doubleToLongBits( dval ) & ~signMask;
	int binexp = (int)(lbits >>> expShift);
	lbits &= fractMask;
	if ( binexp > 0 ){
	    lbits |= fractHOB;
	} else {
	    if ( lbits == 0L )
		throw new RuntimeException("Assertion botch: doubleToBigInt(0.0)");
	    binexp +=1;
	    while ( (lbits & fractHOB ) == 0L){
		lbits <<= 1;
		binexp -= 1;
	    }
	}
	binexp -= expBias;
	int nbits = countBits( lbits );
	/*
	 * We now know where the high-order 1 bit is,
	 * and we know how many there are.
	 */
	int lowOrderZeros = expShift+1-nbits;
	lbits >>>= lowOrderZeros;

	bigIntExp = binexp+1-nbits;
	bigIntNBits = nbits;
	return new FDBigInt( lbits );
    }

    /*
     * Compute a number that is the ULP of the given value,
     * for purposes of addition/subtraction. Generally easy.
     * More difficult if subtracting and the argument
     * is a normalized a power of 2, as the ULP changes at these points.
     */
    private static double
    ulp( double dval, boolean subtracting ){
	long lbits = Double.doubleToLongBits( dval ) & ~signMask;
	int binexp = (int)(lbits >>> expShift);
	double ulpval;
	if ( subtracting && ( binexp >= expShift ) && ((lbits&fractMask) == 0L) ){
	    // for subtraction from normalized, powers of 2,
	    // use next-smaller exponent
	    binexp -= 1;
	}
	if ( binexp > expShift ){
	    ulpval = Double.longBitsToDouble( ((long)(binexp-expShift))<<expShift );
	} else if ( binexp == 0 ){
	    ulpval = Double.MIN_VALUE;
	} else {
	    ulpval = Double.longBitsToDouble( 1L<<(binexp-1) );
	}
	if ( subtracting ) ulpval = - ulpval;

	return ulpval;
    }

    /*
     * Round a double to a float.
     * In addition to the fraction bits of the double,
     * look at the class instance variable roundDir,
     * which should help us avoid double-rounding error.
     * roundDir was set in hardValueOf if the estimate was
     * close enough, but not exact. It tells us which direction
     * of rounding is preferred.
     */
    float
    stickyRound( double dval ){
	long lbits = Double.doubleToLongBits( dval );
	long binexp = lbits & expMask;
	if ( binexp == 0L || binexp == expMask ){
	    // what we have here is special.
	    // don't worry, the right thing will happen.
	    return (float) dval;
	}
	lbits += (long)roundDir; // hack-o-matic.
	return (float)Double.longBitsToDouble( lbits );
    }


    /*
     * This is the easy subcase --
     * all the significant bits, after scaling, are held in lvalue.
     * negSign and decExponent tell us what processing and scaling
     * has already been done. Exceptional cases have already been
     * stripped out.
     * In particular:
     * lvalue is a finite number (not Inf, nor NaN)
     * lvalue > 0L (not zero, nor negative).
     *
     * The only reason that we develop the digits here, rather than
     * calling on Long.toString() is that we can do it a little faster,
     * and besides want to treat trailing 0s specially. If Long.toString
     * changes, we should re-evaluate this strategy!
     */
    private void
    developLongDigits( int decExponent, long lvalue, long insignificant ){
	char digits[];
	int  ndigits;
	int  digitno;
	int  c;
	//
	// Discard non-significant low-order bits, while rounding,
	// up to insignificant value.
	int i;
	for ( i = 0; insignificant >= 10L; i++ )
	    insignificant /= 10L;
	if ( i != 0 ){
	    long pow10 = long5pow[i] << i; // 10^i == 5^i * 2^i;
	    long residue = lvalue % pow10;
	    lvalue /= pow10;
	    decExponent += i;
	    if ( residue >= (pow10>>1) ){
		// round up based on the low-order bits we're discarding
		lvalue++;
	    }
	}
	if ( lvalue <= Integer.MAX_VALUE ){
	    if ( lvalue <= 0L )
		throw new RuntimeException("Assertion botch: value "+lvalue+" <= 0");

	    // even easier subcase!
	    // can do int arithmetic rather than long!
	    int  ivalue = (int)lvalue;
	    digits = new char[ ndigits=10 ];
	    digitno = ndigits-1;
	    c = ivalue%10;
	    ivalue /= 10;
	    while ( c == 0 ){
		decExponent++;
		c = ivalue%10;
		ivalue /= 10;
	    }
	    while ( ivalue != 0){
		digits[digitno--] = (char)(c+'0');
		decExponent++;
		c = ivalue%10;
		ivalue /= 10;
	    }
	    digits[digitno] = (char)(c+'0');
	} else {
	    // same algorithm as above (same bugs, too )
	    // but using long arithmetic.
	    digits = new char[ ndigits=20 ];
	    digitno = ndigits-1;
	    c = (int)(lvalue%10L);
	    lvalue /= 10L;
	    while ( c == 0 ){
		decExponent++;
		c = (int)(lvalue%10L);
		lvalue /= 10L;
	    }
	    while ( lvalue != 0L ){
		digits[digitno--] = (char)(c+'0');
		decExponent++;
		c = (int)(lvalue%10L);
		lvalue /= 10;
	    }
	    digits[digitno] = (char)(c+'0');
	}
	char result [];
	ndigits -= digitno;
	if ( digitno == 0 )
	    result = digits;
	else {
	    result = new char[ ndigits ];
	    System.arraycopy( digits, digitno, result, 0, ndigits );
	}
	this.digits = result;
	this.decExponent = decExponent+1;
	this.nDigits = ndigits;
    }

    //
    // add one to the least significant digit.
    // in the unlikely event there is a carry out,
    // deal with it.
    // assert that this will only happen where there
    // is only one digit, e.g. (float)1e-44 seems to do it.
    //
    private void
    roundup(){
	int i;
	int q = digits[ i = (nDigits-1)];
	if ( q == '9' ){
	    while ( q == '9' && i > 0 ){
		digits[i] = '0';
		q = digits[--i];
	    }
	    if ( q == '9' ){
		// carryout! High-order 1, rest 0s, larger exp.
		decExponent += 1;
		digits[0] = '1';
		return;
	    }
	    // else fall through.
	}
	digits[i] = (char)(q+1);
    }

    /*
     * FIRST IMPORTANT CONSTRUCTOR: DOUBLE
     */
    public FloatingDecimal( double d )
    {
	long	dBits = Double.doubleToLongBits( d );
	long	fractBits;
	int	binExp;
	int	nSignificantBits;

	// discover and delete sign
	if ( (dBits&signMask) != 0 ){
	    isNegative = true;
	    dBits ^= signMask;
	} else {
	    isNegative = false;
	}
	// Begin to unpack
	// Discover obvious special cases of NaN and Infinity.
	binExp = (int)( (dBits&expMask) >> expShift );
	fractBits = dBits&fractMask;
	if ( binExp == (int)(expMask>>expShift) ) {
	    isExceptional = true;
	    if ( fractBits == 0L ){
		digits =  infinity;
	    } else {
		digits = notANumber;
		isNegative = false; // NaN has no sign!
	    }
	    nDigits = digits.length;
	    return;
	}
	isExceptional = false;
	// Finish unpacking
	// Normalize denormalized numbers.
	// Insert assumed high-order bit for normalized numbers.
	// Subtract exponent bias.
	if ( binExp == 0 ){
	    if ( fractBits == 0L ){
		// not a denorm, just a 0!
		decExponent = 0;
		digits = zero;
		nDigits = 1;
		return;
	    }
	    while ( (fractBits&fractHOB) == 0L ){
		fractBits <<= 1;
		binExp -= 1;
	    }
	    nSignificantBits = expShift + binExp +1; // recall binExp is  - shift count.
	    binExp += 1;
	} else {
	    fractBits |= fractHOB;
	    nSignificantBits = expShift+1;
	}
	binExp -= expBias;
	// call the routine that actually does all the hard work.
	dtoa( binExp, fractBits, nSignificantBits );
    }

    /*
     * SECOND IMPORTANT CONSTRUCTOR: SINGLE
     */
    public FloatingDecimal( float f )
    {
	int	fBits = Float.floatToIntBits( f );
	int	fractBits;
	int	binExp;
	int	nSignificantBits;

	// discover and delete sign
	if ( (fBits&singleSignMask) != 0 ){
	    isNegative = true;
	    fBits ^= singleSignMask;
	} else {
	    isNegative = false;
	}
	// Begin to unpack
	// Discover obvious special cases of NaN and Infinity.
	binExp = (int)( (fBits&singleExpMask) >> singleExpShift );
	fractBits = fBits&singleFractMask;
	if ( binExp == (int)(singleExpMask>>singleExpShift) ) {
	    isExceptional = true;
	    if ( fractBits == 0L ){
		digits =  infinity;
	    } else {
		digits = notANumber;
		isNegative = false; // NaN has no sign!
	    }
	    nDigits = digits.length;
	    return;
	}
	isExceptional = false;
	// Finish unpacking
	// Normalize denormalized numbers.
	// Insert assumed high-order bit for normalized numbers.
	// Subtract exponent bias.
	if ( binExp == 0 ){
	    if ( fractBits == 0 ){
		// not a denorm, just a 0!
		decExponent = 0;
		digits = zero;
		nDigits = 1;
		return;
	    }
	    while ( (fractBits&singleFractHOB) == 0 ){
		fractBits <<= 1;
		binExp -= 1;
	    }
	    nSignificantBits = singleExpShift + binExp +1; // recall binExp is  - shift count.
	    binExp += 1;
	} else {
	    fractBits |= singleFractHOB;
	    nSignificantBits = singleExpShift+1;
	}
	binExp -= singleExpBias;
	// call the routine that actually does all the hard work.
	dtoa( binExp, ((long)fractBits)<<(expShift-singleExpShift), nSignificantBits );
    }

    private void
    dtoa( int binExp, long fractBits, int nSignificantBits )
    {
	int	nFractBits; // number of significant bits of fractBits;
	int	nTinyBits;  // number of these to the right of the point.
	int	decExp;

	// Examine number. Determine if it is an easy case,
	// which we can do pretty trivially using float/long conversion,
	// or whether we must do real work.
	nFractBits = countBits( fractBits );
	nTinyBits = Math.max( 0, nFractBits - binExp - 1 );
	if ( binExp <= maxSmallBinExp && binExp >= minSmallBinExp ){
	    // Look more closely at the number to decide if,
	    // with scaling by 10^nTinyBits, the result will fit in
	    // a long.
	    if ( (nTinyBits < long5pow.length) && ((nFractBits + n5bits[nTinyBits]) < 64 ) ){
		/*
		 * We can do this:
		 * take the fraction bits, which are normalized.
		 * (a) nTinyBits == 0: Shift left or right appropriately
		 *     to align the binary point at the extreme right, i.e.
		 *     where a long int point is expected to be. The integer
		 *     result is easily converted to a string.
		 * (b) nTinyBits > 0: Shift right by expShift-nFractBits,
		 *     which effectively converts to long and scales by
		 *     2^nTinyBits. Then multiply by 5^nTinyBits to
		 *     complete the scaling. We know this won't overflow
		 *     because we just counted the number of bits necessary
		 *     in the result. The integer you get from this can
		 *     then be converted to a string pretty easily.
		 */
		long halfULP;
		if ( nTinyBits == 0 ) {
		    if ( binExp > nSignificantBits ){
			halfULP = 1L << ( binExp-nSignificantBits-1);
		    } else {
			halfULP = 0L;
		    }
		    if ( binExp >= expShift ){
			fractBits <<= (binExp-expShift);
		    } else {
			fractBits >>>= (expShift-binExp) ;
		    }
		    developLongDigits( 0, fractBits, halfULP );
		    return;
		}
		/*
		 * The following causes excess digits to be printed
		 * out in the single-float case. Our manipulation of
		 * halfULP here is apparently not correct. If we
		 * better understand how this works, perhaps we can
		 * use this special case again. But for the time being,
		 * we do not.
		 * else {
		 *     fractBits >>>= expShift+1-nFractBits;
		 *     fractBits *= long5pow[ nTinyBits ];
		 *     halfULP = long5pow[ nTinyBits ] >> (1+nSignificantBits-nFractBits);
		 *     developLongDigits( -nTinyBits, fractBits, halfULP );
		 *     return;
		 * }
		 */
	    }
	}
	/*
	 * This is the hard case. We are going to compute large positive
	 * integers B and S and integer decExp, s.t.
	 *	d = ( B / S ) * 10^decExp
	 *	1 <= B / S < 10
	 * Obvious choices are:
	 *	decExp = floor( log10(d) )
	 * 	B      = d * 2^nTinyBits * 10^max( 0, -decExp )
	 *	S      = 10^max( 0, decExp) * 2^nTinyBits
	 * (noting that nTinyBits has already been forced to non-negative)
	 * I am also going to compute a large positive integer
	 *	M      = (1/2^nSignificantBits) * 2^nTinyBits * 10^max( 0, -decExp )
	 * i.e. M is (1/2) of the ULP of d, scaled like B.
	 * When we iterate through dividing B/S and picking off the
	 * quotient bits, we will know when to stop when the remainder
	 * is <= M.
	 *
	 * We keep track of powers of 2 and powers of 5.
	 */

	/*
	 * Estimate decimal exponent. (If it is small-ish,
	 * we could double-check.)
	 *
	 * First, scale the mantissa bits such that 1 <= d2 < 2.
	 * We are then going to estimate
	 *	    log10(d2) ~=~  (d2-1.5)/1.5 + log(1.5)
	 * and so we can estimate
	 *      log10(d) ~=~ log10(d2) + binExp * log10(2)
	 * take the floor and call it decExp.
	 * FIXME -- use more precise constants here. It costs no more.
	 */
	double d2 = Double.longBitsToDouble(
	    expOne | ( fractBits &~ fractHOB ) );
	decExp = (int)Math.floor(
	    (d2-1.5D)*0.289529654D + 0.176091259 + (double)binExp * 0.301029995663981 );
	int B2, B5; // powers of 2 and powers of 5, respectively, in B
	int S2, S5; // powers of 2 and powers of 5, respectively, in S
	int M2, M5; // powers of 2 and powers of 5, respectively, in M
	int Bbits; // binary digits needed to represent B, approx.
	int tenSbits; // binary digits needed to represent 10*S, approx.
	FDBigInt Sval, Bval, Mval;

	B5 = Math.max( 0, -decExp );
	B2 = B5 + nTinyBits + binExp;

	S5 = Math.max( 0, decExp );
	S2 = S5 + nTinyBits;

	M5 = B5;
	M2 = B2 - nSignificantBits;

	/*
	 * the long integer fractBits contains the (nFractBits) interesting
	 * bits from the mantissa of d ( hidden 1 added if necessary) followed
	 * by (expShift+1-nFractBits) zeros. In the interest of compactness,
	 * I will shift out those zeros before turning fractBits into a
	 * FDBigInt. The resulting whole number will be
	 * 	d * 2^(nFractBits-1-binExp).
	 */
	fractBits >>>= (expShift+1-nFractBits);
	B2 -= nFractBits-1;
	int common2factor = Math.min( B2, S2 );
	B2 -= common2factor;
	S2 -= common2factor;
	M2 -= common2factor;

	/*
	 * HACK!! For exact powers of two, the next smallest number
	 * is only half as far away as we think (because the meaning of
	 * ULP changes at power-of-two bounds) for this reason, we
	 * hack M2. Hope this works.
	 */
	if ( nFractBits == 1 )
	    M2 -= 1;

	if ( M2 < 0 ){
	    // oops.
	    // since we cannot scale M down far enough,
	    // we must scale the other values up.
	    B2 -= M2;
	    S2 -= M2;
	    M2 =  0;
	}
	/*
	 * Construct, Scale, iterate.
	 * Some day, we'll write a stopping test that takes
	 * account of the assymetry of the spacing of floating-point
	 * numbers below perfect powers of 2
	 * 26 Sept 96 is not that day.
	 * So we use a symmetric test.
	 */
	char digits[] = this.digits = new char[18];
	int  ndigit = 0;
	boolean low, high;
	long lowDigitDifference;
	int  q;

	/*
	 * Detect the special cases where all the numbers we are about
	 * to compute will fit in int or long integers.
	 * In these cases, we will avoid doing FDBigInt arithmetic.
	 * We use the same algorithms, except that we "normalize"
	 * our FDBigInts before iterating. This is to make division easier,
	 * as it makes our fist guess (quotient of high-order words)
	 * more accurate!
	 *
	 * Some day, we'll write a stopping test that takes
	 * account of the assymetry of the spacing of floating-point
	 * numbers below perfect powers of 2
	 * 26 Sept 96 is not that day.
	 * So we use a symmetric test.
	 */
	Bbits = nFractBits + B2 + (( B5 < n5bits.length )? n5bits[B5] : ( B5*3 ));
	tenSbits = S2+1 + (( (S5+1) < n5bits.length )? n5bits[(S5+1)] : ( (S5+1)*3 ));
	if ( Bbits < 64 && tenSbits < 64){
	    if ( Bbits < 32 && tenSbits < 32){
		// wa-hoo! They're all ints!
		int b = ((int)fractBits * small5pow[B5] ) << B2;
		int s = small5pow[S5] << S2;
		int m = small5pow[M5] << M2;
		int tens = s * 10;
		/*
		 * Unroll the first iteration. If our decExp estimate
		 * was too high, our first quotient will be zero. In this
		 * case, we discard it and decrement decExp.
		 */
		ndigit = 0;
		q = (int) ( b / s );
		b = 10 * ( b % s );
		m *= 10;
		low  = (b <  m );
		high = (b+m > tens );
		if ( q >= 10 ){
		    // bummer, dude
		    throw new RuntimeException( "Assertion botch: excessivly large digit "+q);
		} else if ( (q == 0) && ! high ){
		    // oops. Usually ignore leading zero.
		    decExp--;
		} else {
		    digits[ndigit++] = (char)('0' + q);
		}
		/*
		 * HACK! Java spec sez that we always have at least
		 * one digit after the . in either F- or E-form output.
		 * Thus we will need more than one digit if we're using
		 * E-form
		 */
		if ( decExp <= -3 || decExp >= 8 ){
		    high = low = false;
		}
		while( ! low && ! high ){
		    q = (int) ( b / s );
		    b = 10 * ( b % s );
		    m *= 10;
		    if ( q >= 10 ){
			// bummer, dude
			throw new RuntimeException( "Assertion botch: excessivly large digit "+q);
		    }
		    if ( m > 0L ){
			low  = (b <  m );
			high = (b+m > tens );
		    } else {
			// hack -- m might overflow!
			// in this case, it is certainly > b,
			// which won't
			// and b+m > tens, too, since that has overflowed
			// either!
			low = true;
			high = true;
		    }
		    digits[ndigit++] = (char)('0' + q);
		}
		lowDigitDifference = (b<<1) - tens;
	    } else {
		// still good! they're all longs!
		long b = (fractBits * long5pow[B5] ) << B2;
		long s = long5pow[S5] << S2;
		long m = long5pow[M5] << M2;
		long tens = s * 10L;
		/*
		 * Unroll the first iteration. If our decExp estimate
		 * was too high, our first quotient will be zero. In this
		 * case, we discard it and decrement decExp.
		 */
		ndigit = 0;
		q = (int) ( b / s );
		b = 10L * ( b % s );
		m *= 10L;
		low  = (b <  m );
		high = (b+m > tens );
		if ( q >= 10 ){
		    // bummer, dude
		    throw new RuntimeException( "Assertion botch: excessivly large digit "+q);
		} else if ( (q == 0) && ! high ){
		    // oops. Usually ignore leading zero.
		    decExp--;
		} else {
		    digits[ndigit++] = (char)('0' + q);
		}
		/*
		 * HACK! Java spec sez that we always have at least
		 * one digit after the . in either F- or E-form output.
		 * Thus we will need more than one digit if we're using
		 * E-form
		 */
		if ( decExp <= -3 || decExp >= 8 ){
		    high = low = false;
		}
		while( ! low && ! high ){
		    q = (int) ( b / s );
		    b = 10 * ( b % s );
		    m *= 10;
		    if ( q >= 10 ){
			// bummer, dude
			throw new RuntimeException( "Assertion botch: excessivly large digit "+q);
		    }
		    if ( m > 0L ){
			low  = (b <  m );
			high = (b+m > tens );
		    } else {
			// hack -- m might overflow!
			// in this case, it is certainly > b,
			// which won't
			// and b+m > tens, too, since that has overflowed
			// either!
			low = true;
			high = true;
		    }
		    digits[ndigit++] = (char)('0' + q);
		}
		lowDigitDifference = (b<<1) - tens;
	    }
	} else {
	    FDBigInt tenSval;
	    int  shiftBias;

	    /*
	     * We really must do FDBigInt arithmetic.
	     * Fist, construct our FDBigInt initial values.
	     */
	    Bval = multPow52( new FDBigInt( fractBits  ), B5, B2 );
	    Sval = constructPow52( S5, S2 );
	    Mval = constructPow52( M5, M2 );


	    // normalize so that division works better
	    Bval.lshiftMe( shiftBias = Sval.normalizeMe() );
	    Mval.lshiftMe( shiftBias );
	    tenSval = Sval.mult( 10 );
	    /*
	     * Unroll the first iteration. If our decExp estimate
	     * was too high, our first quotient will be zero. In this
	     * case, we discard it and decrement decExp.
	     */
	    ndigit = 0;
	    q = Bval.quoRemIteration( Sval );
	    Mval = Mval.mult( 10 );
	    low  = (Bval.cmp( Mval ) < 0);
	    high = (Bval.add( Mval ).cmp( tenSval ) > 0 );
	    if ( q >= 10 ){
		// bummer, dude
		throw new RuntimeException( "Assertion botch: excessivly large digit "+q);
	    } else if ( (q == 0) && ! high ){
		// oops. Usually ignore leading zero.
		decExp--;
	    } else {
		digits[ndigit++] = (char)('0' + q);
	    }
	    /*
	     * HACK! Java spec sez that we always have at least
	     * one digit after the . in either F- or E-form output.
	     * Thus we will need more than one digit if we're using
	     * E-form
	     */
	    if ( decExp <= -3 || decExp >= 8 ){
		high = low = false;
	    }
	    while( ! low && ! high ){
		q = Bval.quoRemIteration( Sval );
		Mval = Mval.mult( 10 );
		if ( q >= 10 ){
		    // bummer, dude
		    throw new RuntimeException( "Assertion botch: excessivly large digit "+q);
		}
		low  = (Bval.cmp( Mval ) < 0);
		high = (Bval.add( Mval ).cmp( tenSval ) > 0 );
		digits[ndigit++] = (char)('0' + q);
	    }
	    if ( high && low ){
		Bval.lshiftMe(1);
		lowDigitDifference = Bval.cmp(tenSval);
	    } else
		lowDigitDifference = 0L; // this here only for flow analysis!
	}
	this.decExponent = decExp+1;
	this.digits = digits;
	this.nDigits = ndigit;
	/*
	 * Last digit gets rounded based on stopping condition.
	 */
	if ( high ){
	    if ( low ){
		if ( lowDigitDifference == 0L ){
		    // it's a tie!
		    // choose based on which digits we like.
		    if ( (digits[nDigits-1]&1) != 0 ) roundup();
		} else if ( lowDigitDifference > 0 ){
		    roundup();
		}
	    } else {
		roundup();
	    }
	}
    }

    public String
    toString(){
	// most brain-dead version
	StringBuffer result = new StringBuffer( nDigits+8 );
	if ( isNegative ){ result.append( '-' ); }
	if ( isExceptional ){
	    result.append( digits, 0, nDigits );
	} else {
	    result.append( "0.");
	    result.append( digits, 0, nDigits );
	    result.append('e');
	    result.append( decExponent );
	}
	return new String(result);
    }

    public String
    toJavaFormatString(){
	char result[] = new char[ nDigits + 10 ];
	int  i = 0;
	if ( isNegative ){ result[0] = '-'; i = 1; }
	if ( isExceptional ){
	    System.arraycopy( digits, 0, result, i, nDigits );
	    i += nDigits;
	} else {
	    if ( decExponent > 0 && decExponent < 8 ){
		// print digits.digits.
		int charLength = Math.min( nDigits, decExponent );
		System.arraycopy( digits, 0, result, i, charLength );
		i += charLength;
		if ( charLength < decExponent ){
		    charLength = decExponent-charLength;
		    System.arraycopy( zero, 0, result, i, charLength );
		    i += charLength;
		    result[i++] = '.';
		    result[i++] = '0';
		} else {
		    result[i++] = '.';
		    if ( charLength < nDigits ){
			int t = nDigits - charLength;
			System.arraycopy( digits, charLength, result, i, t );
			i += t;
		    } else{
			result[i++] = '0';
		    }
		}
	    } else if ( decExponent <=0 && decExponent > -3 ){
		result[i++] = '0';
		result[i++] = '.';
		if ( decExponent != 0 ){
		    System.arraycopy( zero, 0, result, i, -decExponent );
		    i -= decExponent;
		}
		System.arraycopy( digits, 0, result, i, nDigits );
		i += nDigits;
	    } else {
		result[i++] = digits[0];
		result[i++] = '.';
		if ( nDigits > 1 ){
		    System.arraycopy( digits, 1, result, i, nDigits-1 );
		    i += nDigits-1;
		} else {
		    result[i++] = '0';
		}
		result[i++] = 'E';
		int e;
		if ( decExponent <= 0 ){
		    result[i++] = '-';
		    e = -decExponent+1;
		} else {
		    e = decExponent-1;
		}
		// decExponent has 1, 2, or 3, digits
		if ( e <= 9 ) {
		    result[i++] = (char)( e+'0' );
		} else if ( e <= 99 ){
		    result[i++] = (char)( e10 +'0' );
		    result[i++] = (char)( e%10 + '0' );
		} else {
		    result[i++] = (char)(e100+'0');
		    e %= 100;
		    result[i++] = (char)(e10+'0');
		    result[i++] = (char)( e%10 + '0' );
		}
	    }
	}
	return new String(result, 0, i);
    }

    public static FloatingDecimal
    readJavaFormatString( String in ) throws NumberFormatException {
	boolean isNegative = false;
	boolean signSeen   = false;
	int     decExp;
	char	c;

    parseNumber:
	try{
	    in = in.trim(); // don't fool around with white space.
			   // throws NullPointerException if null
	    int	l = in.length();
	    if ( l == 0 ) throw new NumberFormatException("empty String");
	    int	i = 0;
	    switch ( c = in.charAt( i ) ){
	    case '-':
		isNegative = true;
		//FALLTHROUGH
	    case '+':
		i++;
		signSeen = true;
	    }
	    // Would handle NaN and Infinity here, but it isn't
	    // part of the spec!
	    //
	    char[] digits = new char[ l ];
	    int    nDigits= 0;
	    boolean decSeen = false;
	    int	decPt = 0;
	    int	nLeadZero = 0;
	    int	nTrailZero= 0;
	digitLoop:
	    while ( i < l ){
		switch ( c = in.charAt( i ) ){
		case '0':
		    if ( nDigits > 0 ){
			nTrailZero += 1;
		    } else {
			nLeadZero += 1;
		    }
		    break; // out of switch.
		case '1':
		case '2':
		case '3':
		case '4':
		case '5':
		case '6':
		case '7':
		case '8':
		case '9':
		    while ( nTrailZero > 0 ){
			digits[nDigits++] = '0';
			nTrailZero -= 1;
		    }
		    digits[nDigits++] = c;
		    break; // out of switch.
		case '.':
		    if ( decSeen ){
			// already saw one ., this is the 2nd.
			throw new NumberFormatException("multiple points");
		    }
		    decPt = i;
		    if ( signSeen ){
			decPt -= 1;
		    }
		    decSeen = true;
		    break; // out of switch.
		default:
		    break digitLoop;
		}
		i++;
	    }
	    /*
	     * At this point, we've scanned all the digits and decimal
	     * point we're going to see. Trim off leading and trailing
	     * zeros, which will just confuse us later, and adjust
	     * our initial decimal exponent accordingly.
	     * To review:
	     * we have seen i total characters.
	     * nLeadZero of them were zeros before any other digits.
	     * nTrailZero of them were zeros after any other digits.
	     * if ( decSeen ), then a . was seen after decPt characters
	     * ( including leading zeros which have been discarded )
	     * nDigits characters were neither lead nor trailing
	     * zeros, nor point
	     */
	    /*
	     * special hack: if we saw no non-zero digits, then the
	     * answer is zero!
	     * Unfortunately, we feel honor-bound to keep parsing!
	     */
	    if ( nDigits == 0 ){
		digits = zero;
		nDigits = 1;
		if ( nLeadZero == 0 ){
		    // we saw NO DIGITS AT ALL,
		    // not even a crummy 0!
		    // this is not allowed.
		    break parseNumber; // go throw exception
		}

	    }

	    /* Our initial exponent is decPt, adjusted by the number of
	     * discarded zeros. Or, if there was no decPt,
	     * then its just nDigits adjusted by discarded trailing zeros.
	     */
	    if ( decSeen ){
		decExp = decPt - nLeadZero;
	    } else {
		decExp = nDigits+nTrailZero;
	    }

	    /*
	     * Look for 'e' or 'E' and an optionally signed integer.
	     */
	    if ( (i < l) &&  ((c = in.charAt(i) )=='e') || (c == 'E') ){
		int expSign = 1;
		int expVal  = 0;
		int reallyBig = Integer.MAX_VALUE / 10;
		boolean expOverflow = false;
		switch( in.charAt(++i) ){
		case '-':
		    expSign = -1;
		    //FALLTHROUGH
		case '+':
		    i++;
		}
		int expAt = i;
	    expLoop:
		while ( i < l  ){
		    if ( expVal >= reallyBig ){
			// the next character will cause integer
			// overflow.
			expOverflow = true;
		    }
		    switch ( c = in.charAt(i++) ){
		    case '0':
		    case '1':
		    case '2':
		    case '3':
		    case '4':
		    case '5':
		    case '6':
		    case '7':
		    case '8':
		    case '9':
			expVal = expVal*10 + ( (int)c - (int)'0' );
			continue;
		    default:
			i--;	       // back up.
			break expLoop; // stop parsing exponent.
		    }
		}
		int expLimit = bigDecimalExponent+nDigits+nTrailZero;
		if ( expOverflow || ( expVal > expLimit ) ){
		    //
		    // The intent here is to end up with
		    // infinity or zero, as appropriate.
		    // The reason for yielding such a small decExponent,
		    // rather than something intuitive such as
		    // expSign*Integer.MAX_VALUE, is that this value
		    // is subject to further manipulation in
		    // doubleValue() and floatValue(), and I don't want
		    // it to be able to cause overflow there!
		    // (The only way we can get into trouble here is for
		    // really outrageous nDigits+nTrailZero, such as 2 billion. )
		    //
		    decExp = expSign*expLimit;
		} else {
		    // this should not overflow, since we tested
		    // for expVal > (MAX+N), where N >= abs(decExp)
		    decExp = decExp + expSign*expVal;
		}

		// if we saw something not a digit ( or end of string )
		// after the [Ee][+-], without seeing any digits at all
		// this is certainly an error. If we saw some digits,
		// but then some trailing garbage, that might be ok.
		// so we just fall through in that case.
		// HUMBUG
                if ( i == expAt ) 
		    break parseNumber; // certainly bad
	    }
	    /*
	     * We parsed everything we could.
	     * If there are leftovers, then this is not good input!
	     */
	    if ( i < l &&
                ((i != l - 1) ||
                (in.charAt(i) != 'f' &&
                 in.charAt(i) != 'F' &&
                 in.charAt(i) != 'd' &&
                 in.charAt(i) != 'D'))) {
                break parseNumber; // go throw exception
            }

	    return new FloatingDecimal( isNegative, decExp, digits, nDigits,  false );
	} catch ( StringIndexOutOfBoundsException e ){ }
	throw new NumberFormatException( in );
    }

    /*
     * Take a FloatingDecimal, which we presumably just scanned in,
     * and find out what its value is, as a double.
     *
     * AS A SIDE EFFECT, SET roundDir TO INDICATE PREFERRED
     * ROUNDING DIRECTION in case the result is really destined
     * for a single-precision float.
     */

    public double
    doubleValue(){
	int	kDigits = Math.min( nDigits, maxDecimalDigits+1 );
	long	lValue;
	double	dValue;
	double  rValue, tValue;

	roundDir = 0;

	/*
	 * convert the lead kDigits to a long integer.
	 */
	// (special performance hack: start to do it using int)
	int iValue = (int)digits[0]-(int)'0';
	int iDigits = Math.min( kDigits, intDecimalDigits );
	for ( int i=1; i < iDigits; i++ ){
	    iValue = iValue*10 + (int)digits[i]-(int)'0';
	}
	lValue = (long)iValue;
	for ( int i=iDigits; i < kDigits; i++ ){
	    lValue = lValue*10L + (long)((int)digits[i]-(int)'0');
	}
	dValue = (double)lValue;
	int exp = decExponent-kDigits;
	/*
	 * lValue now contains a long integer with the value of
	 * the first kDigits digits of the number.
	 * dValue contains the (double) of the same.
	 */

	if ( nDigits <= maxDecimalDigits ){
	    /*
	     * possibly an easy case.
	     * We know that the digits can be represented
	     * exactly. And if the exponent isn't too outrageous,
	     * the whole thing can be done with one operation,
	     * thus one rounding error.
             * Note that all our constructors trim all leading and
             * trailing zeros, so simple values (including zero)
             * will always end up here
	     */
	    if (exp == 0 || dValue == 0.0)
                return (isNegative)? -dValue : dValue; // small floating integer
	    else if ( exp >= 0 ){
		if ( exp <= maxSmallTen ){
		    /*
		     * Can get the answer with one operation,
		     * thus one roundoff.
		     */
		    rValue = dValue * small10pow[exp];
		    if ( mustSetRoundDir ){
			tValue = rValue / small10pow[exp];
			roundDir = ( tValue ==  dValue ) ? 0
			          :( tValue < dValue ) ? 1
			          : -1;
		    }
		    return (isNegative)? -rValue : rValue;
		}
		int slop = maxDecimalDigits - kDigits;
		if ( exp <= maxSmallTen+slop ){
		    /*
		     * We can multiply dValue by 10^(slop)
		     * and it is still "small" and exact.
		     * Then we can multiply by 10^(exp-slop)
		     * with one rounding.
		     */
		    dValue *= small10pow[slop];
		    rValue = dValue * small10pow[exp-slop];

		    if ( mustSetRoundDir ){
			tValue = rValue / small10pow[exp-slop];
			roundDir = ( tValue ==  dValue ) ? 0
				  :( tValue < dValue ) ? 1
				  : -1;
		    }
		    return (isNegative)? -rValue : rValue;
		}
		/*
		 * Else we have a hard case with a positive exp.
		 */
	    } else {
		if ( exp >= -maxSmallTen ){
		    /*
		     * Can get the answer in one division.
		     */
		    rValue = dValue / small10pow[-exp];
		    tValue = rValue * small10pow[-exp];
		    if ( mustSetRoundDir ){
			roundDir = ( tValue ==  dValue ) ? 0
				  :( tValue < dValue ) ? 1
				  : -1;
		    }
		    return (isNegative)? -rValue : rValue;
		}
		/*
		 * Else we have a hard case with a negative exp.
		 */
	    }
	}

	/*
	 * Harder cases:
	 * The sum of digits plus exponent is greater than
	 * what we think we can do with one error.
	 *
	 * Start by approximating the right answer by,
	 * naively, scaling by powers of 10.
	 */
	if ( exp > 0 ){
	    if ( decExponent > maxDecimalExponent+1 ){
		/*
		 * Lets face it. This is going to be
		 * Infinity. Cut to the chase.
		 */
		return (isNegative)? Double.NEGATIVE_INFINITY : Double.POSITIVE_INFINITY;
	    }
	    if ( (exp&15) != 0 ){
		dValue *= small10pow[exp&15];
	    }
	    if ( (exp>>=4) != 0 ){
		int j;
		for( j = 0; exp > 1; j++, exp>>=1 ){
		    if ( (exp&1)!=0)
			dValue *= big10pow[j];
		}
		/*
		 * The reason for the weird exp > 1 condition
		 * in the above loop was so that the last multiply
		 * would get unrolled. We handle it here.
		 * It could overflow.
		 */
		double t = dValue * big10pow[j];
		if ( Double.isInfinite( t ) ){
		    /*
		     * It did overflow.
		     * Look more closely at the result.
		     * If the exponent is just one too large,
		     * then use the maximum finite as our estimate
		     * value. Else call the result infinity
		     * and punt it.
		     * ( I presume this could happen because
		     * rounding forces the result here to be
		     * an ULP or two larger than
		     * Double.MAX_VALUE ).
		     */
		    t = dValue / 2.0;
		    t *= big10pow[j];
		    if ( Double.isInfinite( t ) ){
			return (isNegative)? Double.NEGATIVE_INFINITY : Double.POSITIVE_INFINITY;
		    }
		    t = Double.MAX_VALUE;
		}
		dValue = t;
	    }
	} else if ( exp < 0 ){
	    exp = -exp;
	    if ( decExponent < minDecimalExponent-1 ){
		/*
		 * Lets face it. This is going to be
		 * zero. Cut to the chase.
		 */
		return (isNegative)? -0.0 : 0.0;
	    }
	    if ( (exp&15) != 0 ){
		dValue /= small10pow[exp&15];
	    }
	    if ( (exp>>=4) != 0 ){
		int j;
		for( j = 0; exp > 1; j++, exp>>=1 ){
		    if ( (exp&1)!=0)
			dValue *= tiny10pow[j];
		}
		/*
		 * The reason for the weird exp > 1 condition
		 * in the above loop was so that the last multiply
		 * would get unrolled. We handle it here.
		 * It could underflow.
		 */
		double t = dValue * tiny10pow[j];
		if ( t == 0.0 ){
		    /*
		     * It did underflow.
		     * Look more closely at the result.
		     * If the exponent is just one too small,
		     * then use the minimum finite as our estimate
		     * value. Else call the result 0.0
		     * and punt it.
		     * ( I presume this could happen because
		     * rounding forces the result here to be
		     * an ULP or two less than
		     * Double.MIN_VALUE ).
		     */
		    t = dValue * 2.0;
		    t *= tiny10pow[j];
		    if ( t == 0.0 ){
			return (isNegative)? -0.0 : 0.0;
		    }
		    t = Double.MIN_VALUE;
		}
		dValue = t;
	    }
	}

	/*
	 * dValue is now approximately the result.
	 * The hard part is adjusting it, by comparison
	 * with FDBigInt arithmetic.
	 * Formulate the EXACT big-number result as
	 * bigD0 * 10^exp
	 */
	FDBigInt bigD0 = new FDBigInt( lValue, digits, kDigits, nDigits );
	exp   = decExponent - nDigits;

    correctionLoop:
	while(true){
	    /* AS A SIDE EFFECT, THIS METHOD WILL SET THE INSTANCE VARIABLES
	     * bigIntExp and bigIntNBits
	     */
	    FDBigInt bigB = doubleToBigInt( dValue );

	    /*
	     * Scale bigD, bigB appropriately for
	     * big-integer operations.
	     * Naively, we multipy by powers of ten
	     * and powers of two. What we actually do
	     * is keep track of the powers of 5 and
	     * powers of 2 we would use, then factor out
	     * common divisors before doing the work.
	     */
	    int B2, B5; // powers of 2, 5 in bigB
	    int	D2, D5;	// powers of 2, 5 in bigD
	    int Ulp2;   // powers of 2 in halfUlp.
	    if ( exp >= 0 ){
		B2 = B5 = 0;
		D2 = D5 = exp;
	    } else {
		B2 = B5 = -exp;
		D2 = D5 = 0;
	    }
	    if ( bigIntExp >= 0 ){
		B2 += bigIntExp;
	    } else {
		D2 -= bigIntExp;
	    }
	    Ulp2 = B2;
	    // shift bigB and bigD left by a number s. t.
	    // halfUlp is still an integer.
	    int hulpbias;
	    if ( bigIntExp+bigIntNBits <= -expBias+1 ){
		// This is going to be a denormalized number
		// (if not actually zero).
		// half an ULP is at 2^-(expBias+expShift+1)
		hulpbias = bigIntExp+ expBias + expShift;
	    } else {
		hulpbias = expShift + 2 - bigIntNBits;
	    }
	    B2 += hulpbias;
	    D2 += hulpbias;
	    // if there are common factors of 2, we might just as well
	    // factor them out, as they add nothing useful.
	    int common2 = Math.min( B2, Math.min( D2, Ulp2 ) );
	    B2 -= common2;
	    D2 -= common2;
	    Ulp2 -= common2;
	    // do multiplications by powers of 5 and 2
	    bigB = multPow52( bigB, B5, B2 );
	    FDBigInt bigD = multPow52( new FDBigInt( bigD0 ), D5, D2 );
	    //
	    // to recap:
	    // bigB is the scaled-big-int version of our floating-point
	    // candidate.
	    // bigD is the scaled-big-int version of the exact value
	    // as we understand it.
	    // halfUlp is 1/2 an ulp of bigB, except for special cases
	    // of exact powers of 2
	    //
	    // the plan is to compare bigB with bigD, and if the difference
	    // is less than halfUlp, then we're satisfied. Otherwise,
	    // use the ratio of difference to halfUlp to calculate a fudge
	    // factor to add to the floating value, then go 'round again.
	    //
	    FDBigInt diff;
	    int cmpResult;
	    boolean overvalue;
	    if ( (cmpResult = bigB.cmp( bigD ) ) > 0 ){
		overvalue = true; // our candidate is too big.
		diff = bigB.sub( bigD );
		if ( (bigIntNBits == 1) && (bigIntExp > -expBias) ){
		    // candidate is a normalized exact power of 2 and
		    // is too big. We will be subtracting.
		    // For our purposes, ulp is the ulp of the
		    // next smaller range.
		    Ulp2 -= 1;
		    if ( Ulp2 < 0 ){
			// rats. Cannot de-scale ulp this far.
			// must scale diff in other direction.
			Ulp2 = 0;
			diff.lshiftMe( 1 );
		    }
		}
	    } else if ( cmpResult < 0 ){
		overvalue = false; // our candidate is too small.
		diff = bigD.sub( bigB );
	    } else {
		// the candidate is exactly right!
		// this happens with surprising fequency
		break correctionLoop;
	    }
	    FDBigInt halfUlp = constructPow52( B5, Ulp2 );
	    if ( (cmpResult = diff.cmp( halfUlp ) ) < 0 ){
		// difference is small.
		// this is close enough
		roundDir = overvalue ? -1 : 1;
		break correctionLoop;
	    } else if ( cmpResult == 0 ){
		// difference is exactly half an ULP
		// round to some other value maybe, then finish
		dValue += 0.5*ulp( dValue, overvalue );
		// should check for bigIntNBits == 1 here??
		roundDir = overvalue ? -1 : 1;
		break correctionLoop;
	    } else {
		// difference is non-trivial.
		// could scale addend by ratio of difference to
		// halfUlp here, if we bothered to compute that difference.
		// Most of the time ( I hope ) it is about 1 anyway.
		dValue += ulp( dValue, overvalue );
		if ( dValue == 0.0 || dValue == Double.POSITIVE_INFINITY )
		     break correctionLoop; // oops. Fell off end of range.
		continue; // try again.
	    }

	}
	return (isNegative)? -dValue : dValue;
    }

    /*
     * Take a FloatingDecimal, which we presumably just scanned in,
     * and find out what its value is, as a float.
     * This is distinct from doubleValue() to avoid the extremely
     * unlikely case of a double rounding error, wherein the converstion
     * to double has one rounding error, and the conversion of that double
     * to a float has another rounding error, IN THE WRONG DIRECTION,
     * ( because of the preference to a zero low-order bit ).
     */

    public float
    floatValue(){
	int	kDigits = Math.min( nDigits, singleMaxDecimalDigits+1 );
	int	iValue;
	float	fValue;

	/*
	 * convert the lead kDigits to an integer.
	 */
	iValue = (int)digits[0]-(int)'0';
	for ( int i=1; i < kDigits; i++ ){
	    iValue = iValue*10 + (int)digits[i]-(int)'0';
	}
	fValue = (float)iValue;
	int exp = decExponent-kDigits;
	/*
	 * iValue now contains an integer with the value of
	 * the first kDigits digits of the number.
	 * fValue contains the (float) of the same.
	 */

	if ( nDigits <= singleMaxDecimalDigits ){
	    /*
	     * possibly an easy case.
	     * We know that the digits can be represented
	     * exactly. And if the exponent isn't too outrageous,
	     * the whole thing can be done with one operation,
	     * thus one rounding error.
             * Note that all our constructors trim all leading and
             * trailing zeros, so simple values (including zero)
             * will always end up here.
	     */
	    if (exp == 0 || fValue == 0.0f)
                return (isNegative)? -fValue : fValue; // small floating integer
	    else if ( exp >= 0 ){
		if ( exp <= singleMaxSmallTen ){
		    /*
		     * Can get the answer with one operation,
		     * thus one roundoff.
		     */
		    fValue *= singleSmall10pow[exp];
		    return (isNegative)? -fValue : fValue;
		}
		int slop = singleMaxDecimalDigits - kDigits;
		if ( exp <= singleMaxSmallTen+slop ){
		    /*
		     * We can multiply dValue by 10^(slop)
		     * and it is still "small" and exact.
		     * Then we can multiply by 10^(exp-slop)
		     * with one rounding.
		     */
		    fValue *= singleSmall10pow[slop];
		    fValue *= singleSmall10pow[exp-slop];
		    return (isNegative)? -fValue : fValue;
		}
		/*
		 * Else we have a hard case with a positive exp.
		 */
	    } else {
		if ( exp >= -singleMaxSmallTen ){
		    /*
		     * Can get the answer in one division.
		     */
		    fValue /= singleSmall10pow[-exp];
		    return (isNegative)? -fValue : fValue;
		}
		/*
		 * Else we have a hard case with a negative exp.
		 */
	    }
	} else if ( (decExponent >= nDigits) && (nDigits+decExponent <= maxDecimalDigits) ){
	    /*
	     * In double-precision, this is an exact floating integer.
	     * So we can compute to double, then shorten to float
	     * with one round, and get the right answer.
	     *
	     * First, finish accumulating digits.
	     * Then convert that integer to a double, multiply
	     * by the appropriate power of ten, and convert to float.
	     */
	    long lValue = (long)iValue;
	    for ( int i=kDigits; i < nDigits; i++ ){
		lValue = lValue*10L + (long)((int)digits[i]-(int)'0');
	    }
	    double dValue = (double)lValue;
	    exp = decExponent-nDigits;
	    dValue *= small10pow[exp];
	    fValue = (float)dValue;
	    return (isNegative)? -fValue : fValue;

	}
	/*
	 * Harder cases:
	 * The sum of digits plus exponent is greater than
	 * what we think we can do with one error.
	 *
	 * Start by weeding out obviously out-of-range
	 * results, then convert to double and go to
	 * common hard-case code.
	 */
	if ( decExponent > singleMaxDecimalExponent+1 ){
	    /*
	     * Lets face it. This is going to be
	     * Infinity. Cut to the chase.
	     */
	    return (isNegative)? Float.NEGATIVE_INFINITY : Float.POSITIVE_INFINITY;
	} else if ( decExponent < singleMinDecimalExponent-1 ){
	    /*
	     * Lets face it. This is going to be
	     * zero. Cut to the chase.
	     */
	    return (isNegative)? -0.0f : 0.0f;
	}

	/*
	 * Here, we do 'way too much work, but throwing away
	 * our partial results, and going and doing the whole
	 * thing as double, then throwing away half the bits that computes
	 * when we convert back to float.
	 *
	 * The alternative is to reproduce the whole multiple-precision
	 * algorythm for float precision, or to try to parameterize it
	 * for common usage. The former will take about 400 lines of code,
	 * and the latter I tried without success. Thus the semi-hack
	 * answer here.
	 */
	mustSetRoundDir = true;
	double dValue = doubleValue();
	return stickyRound( dValue );
    }


    /*
     * All the positive powers of 10 that can be
     * represented exactly in double/float.
     */
    private static final double small10pow[] = {
	1.0e0,
	1.0e1, 1.0e2, 1.0e3, 1.0e4, 1.0e5,
	1.0e6, 1.0e7, 1.0e8, 1.0e9, 1.0e10,
	1.0e11, 1.0e12, 1.0e13, 1.0e14, 1.0e15,
	1.0e16, 1.0e17, 1.0e18, 1.0e19, 1.0e20,
	1.0e21, 1.0e22
    };

    private static final float singleSmall10pow[] = {
	1.0e0f,
	1.0e1f, 1.0e2f, 1.0e3f, 1.0e4f, 1.0e5f,
	1.0e6f, 1.0e7f, 1.0e8f, 1.0e9f, 1.0e10f
    };

    private static final double big10pow[] = {
	1e16, 1e32, 1e64, 1e128, 1e256 };
    private static final double tiny10pow[] = {
	1e-16, 1e-32, 1e-64, 1e-128, 1e-256 };

    private static final int maxSmallTen = small10pow.length-1;
    private static final int singleMaxSmallTen = singleSmall10pow.length-1;

    private static final int small5pow[] = {
	1,
	5,
	5*5,
	5*5*5,
	5*5*5*5,
	5*5*5*5*5,
	5*5*5*5*5*5,
	5*5*5*5*5*5*5,
	5*5*5*5*5*5*5*5,
	5*5*5*5*5*5*5*5*5,
	5*5*5*5*5*5*5*5*5*5,
	5*5*5*5*5*5*5*5*5*5*5,
	5*5*5*5*5*5*5*5*5*5*5*5,
	5*5*5*5*5*5*5*5*5*5*5*5*5
    };


    private static final long long5pow[] = {
	1L,
	5L,
	5L*5,
	5L*5*5,
	5L*5*5*5,
	5L*5*5*5*5,
	5L*5*5*5*5*5,
	5L*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5,
	5L*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5*5,
    };

    // approximately ceil( log2( long5pow[i] ) )
    private static final int n5bits[] = {
	0,
	3,
	5,
	7,
	10,
	12,
	14,
	17,
	19,
	21,
	24,
	26,
	28,
	31,
	33,
	35,
	38,
	40,
	42,
	45,
	47,
	49,
	52,
	54,
	56,
	59,
	61,
    };

    private static final char infinity[] = { 'I', 'n', 'f', 'i', 'n', 'i', 't', 'y' };
    private static final char notANumber[] = { 'N', 'a', 'N' };
    private static final char zero[] = { '0', '0', '0', '0', '0', '0', '0', '0' };

}

/*
 * A really, really simple bigint package
 * tailored to the needs of floating base conversion.
 */
class FDBigInt {
    int	nWords; // number of words used
    int data[]; // value: data[0] is least significant


    public FDBigInt( int v ){
	nWords = 1;
	data = new int[1];
	data[0] = v;
    }

    public FDBigInt( long v ){
	data = new int[2];
	data[0] = (int)v;
	data[1] = (int)(v>>>32);
	nWords = (data[1]==0) ? 1 : 2;
    }

    public FDBigInt( FDBigInt other ){
	data = new int[nWords = other.nWords];
	System.arraycopy( other.data, 0, data, 0, nWords );
    }

    private FDBigInt( int [] d, int n ){
	data = d;
	nWords = n;
    }

    public FDBigInt( long seed, char digit[], int nd0, int nd ){
	int n= (nd+8)/9;	// estimate size needed.
	if ( n < 2 ) n = 2;
	data = new int[n];	// allocate enough space
	data[0] = (int)seed;	// starting value
	data[1] = (int)(seed>>>32);
	nWords = (data[1]==0) ? 1 : 2;
	int i = nd0;
	int limit = nd-5;	// slurp digits 5 at a time.
	int v;
	while ( i < limit ){
	    int ilim = i+5;
	    v = (int)digit[i++]-(int)'0';
	    while( i <ilim ){
		v = 10*v + (int)digit[i++]-(int)'0';
	    }
	    multaddMe( 100000, v); // ... where 100000 is 10^5.
	}
	int factor = 1;
	v = 0;
	while ( i < nd ){
	    v = 10*v + (int)digit[i++]-(int)'0';
	    factor *= 10;
	}
	if ( factor != 1 ){
	    multaddMe( factor, v );
	}
    }

    /*
     * Left shift by c bits.
     * Shifts this in place.
     */
    public void
    lshiftMe( int c )throws IllegalArgumentException {
	if ( c <= 0 ){
	    if ( c == 0 )
		return; // silly.
	    else
		throw new IllegalArgumentException("negative shift count");
	}
	int wordcount = c>>5;
	int bitcount  = c & 0x1f;
	int anticount = 32-bitcount;
	int t[] = data;
	int s[] = data;
	if ( nWords+wordcount+1 > t.length ){
	    // reallocate.
	    t = new int[ nWords+wordcount+1 ];
	}
	int target = nWords+wordcount;
	int src    = nWords-1;
	if ( bitcount == 0 ){
	    // special hack, since an anticount of 32 won't go!
	    System.arraycopy( s, 0, t, wordcount, nWords );
	    target = wordcount-1;
	} else {
	    t[target--] = s[src]>>>anticount;
	    while ( src >= 1 ){
		t[target--] = (s[src]<<bitcount) | (s[--src]>>>anticount);
	    }
	    t[target--] = s[src]<<bitcount;
	}
	while( target >= 0 ){
	    t[target--] = 0;
	}
	data = t;
	nWords += wordcount + 1;
	// may have constructed high-order word of 0.
	// if so, trim it
	while ( nWords > 1 && data[nWords-1] == 0 )
	    nWords--;
    }

    /*
     * normalize this number by shifting until
     * the MSB of the number is at 0x08000000.
     * This is in preparation for quoRemIteration, below.
     * The idea is that, to make division easier, we want the
     * divisor to be "normalized" -- usually this means shifting
     * the MSB into the high words sign bit. But because we know that
     * the quotient will be 0 < q < 10, we would like to arrange that
     * the dividend not span up into another word of precision.
     * (This needs to be explained more clearly!)
     */
    public int
    normalizeMe() throws IllegalArgumentException {
	int src;
	int wordcount = 0;
	int bitcount  = 0;
	int v = 0;
	for ( src= nWords-1 ; src >= 0 && (v=data[src]) == 0 ; src--){
	    wordcount += 1;
	}
	if ( src < 0 ){
	    // oops. Value is zero. Cannot normalize it!
	    throw new IllegalArgumentException("zero value");
	}
	/*
	 * In most cases, we assume that wordcount is zero. This only
	 * makes sense, as we try not to maintain any high-order
	 * words full of zeros. In fact, if there are zeros, we will
	 * simply SHORTEN our number at this point. Watch closely...
	 */
	nWords -= wordcount;
	/*
	 * Compute how far left we have to shift v s.t. its highest-
	 * order bit is in the right place. Then call lshiftMe to
	 * do the work.
	 */
	if ( (v & 0xf0000000) != 0 ){
	    // will have to shift up into the next word.
	    // too bad.
	    for( bitcount = 32 ; (v & 0xf0000000) != 0 ; bitcount-- )
		v >>>= 1;
	} else {
	    while ( v <= 0x000fffff ){
		// hack: byte-at-a-time shifting
		v <<= 8;
		bitcount += 8;
	    }
	    while ( v <= 0x07ffffff ){
		v <<= 1;
		bitcount += 1;
	    }
	}
	if ( bitcount != 0 )
	    lshiftMe( bitcount );
	return bitcount;
    }

    /*
     * Multiply a FDBigInt by an int.
     * Result is a new FDBigInt.
     */
    public FDBigInt
    mult( int iv ) {
	long v = iv;
	int r[];
	long p;

	// guess adequate size of r.
	r = new int[ ( v * ((long)data[nWords-1]&0xffffffffL) > 0xfffffffL ) ? nWords+1 : nWords ];
	p = 0L;
	for( int i=0; i < nWords; i++ ) {
	    p += v * ((long)data[i]&0xffffffffL);
	    r[i] = (int)p;
	    p >>>= 32;
	}
	if ( p == 0L){
	    return new FDBigInt( r, nWords );
	} else {
	    r[nWords] = (int)p;
	    return new FDBigInt( r, nWords+1 );
	}
    }

    /*
     * Multiply a FDBigInt by an int and add another int.
     * Result is computed in place.
     * Hope it fits!
     */
    public void
    multaddMe( int iv, int addend ) {
	long v = iv;
	long p;

	// unroll 0th iteration, doing addition.
	p = v * ((long)data[0]&0xffffffffL) + ((long)addend&0xffffffffL);
	data[0] = (int)p;
	p >>>= 32;
	for( int i=1; i < nWords; i++ ) {
	    p += v * ((long)data[i]&0xffffffffL);
	    data[i] = (int)p;
	    p >>>= 32;
	}
	if ( p != 0L){
	    data[nWords] = (int)p; // will fail noisily if illegal!
	    nWords++;
	}
    }

    /*
     * Multiply a FDBigInt by another FDBigInt.
     * Result is a new FDBigInt.
     */
    public FDBigInt
    mult( FDBigInt other ){
	// crudely guess adequate size for r
	int r[] = new int[ nWords + other.nWords ];
	int i;
	// I think I am promised zeros...

	for( i = 0; i < this.nWords; i++ ){
	    long v = (long)this.data[i] & 0xffffffffL; // UNSIGNED CONVERSION
	    long p = 0L;
	    int j;
	    for( j = 0; j < other.nWords; j++ ){
		p += ((long)r[i+j]&0xffffffffL) + v*((long)other.data[j]&0xffffffffL); // UNSIGNED CONVERSIONS ALL 'ROUND.
		r[i+j] = (int)p;
		p >>>= 32;
	    }
	    r[i+j] = (int)p;
	}
	// compute how much of r we actually needed for all that.
	for ( i = r.length-1; i> 0; i--)
	    if ( r[i] != 0 )
		break;
	return new FDBigInt( r, i+1 );
    }

    /*
     * Add one FDBigInt to another. Return a FDBigInt
     */
    public FDBigInt
    add( FDBigInt other ){
	int i;
	int a[], b[];
	int n, m;
	long c = 0L;
	// arrange such that a.nWords >= b.nWords;
	// n = a.nWords, m = b.nWords
	if ( this.nWords >= other.nWords ){
	    a = this.data;
	    n = this.nWords;
	    b = other.data;
	    m = other.nWords;
	} else {
	    a = other.data;
	    n = other.nWords;
	    b = this.data;
	    m = this.nWords;
	}
	int r[] = new int[ n ];
	for ( i = 0; i < n; i++ ){
	    c += (long)a[i] & 0xffffffffL;
	    if ( i < m ){
		c += (long)b[i] & 0xffffffffL;
	    }
	    r[i] = (int) c;
	    c >>= 32; // signed shift.
	}
	if ( c != 0L ){
	    // oops -- carry out -- need longer result.
	    int s[] = new int[ r.length+1 ];
	    System.arraycopy( r, 0, s, 0, r.length );
	    s[i++] = (int)c;
	    return new FDBigInt( s, i );
	}
	return new FDBigInt( r, i );
    }

    /*
     * Subtract one FDBigInt from another. Return a FDBigInt
     * Assert that the result is positive.
     */
    public FDBigInt
    sub( FDBigInt other ){
	int r[] = new int[ this.nWords ];
	int i;
	int n = this.nWords;
	int m = other.nWords;
	int nzeros = 0;
	long c = 0L;
	for ( i = 0; i < n; i++ ){
	    c += (long)this.data[i] & 0xffffffffL;
	    if ( i < m ){
		c -= (long)other.data[i] & 0xffffffffL;
	    }
	    if ( ( r[i] = (int) c ) == 0 )
		nzeros++;
	    else
		nzeros = 0;
	    c >>= 32; // signed shift.
	}
	if ( c != 0L )
	    throw new RuntimeException("Assertion botch: borrow out of subtract");
	while ( i < m )
	    if ( other.data[i++] != 0 )
		throw new RuntimeException("Assertion botch: negative result of subtract");
	return new FDBigInt( r, n-nzeros );
    }

    /*
     * Compare FDBigInt with another FDBigInt. Return an integer
     * >0: this > other
     *  0: this == other
     * <0: this < other
     */
    public int
    cmp( FDBigInt other ){
        int i;
	if ( this.nWords > other.nWords ){
	    // if any of my high-order words is non-zero,
	    // then the answer is evident
	    int j = other.nWords-1;
	    for ( i = this.nWords-1; i > j ; i-- )
		if ( this.data[i] != 0 ) return 1;
	}else if ( this.nWords < other.nWords ){
	    // if any of other's high-order words is non-zero,
	    // then the answer is evident
	    int j = this.nWords-1;
	    for ( i = other.nWords-1; i > j ; i-- )
		if ( other.data[i] != 0 ) return -1;
	} else{
	    i = this.nWords-1;
	}
	for ( ; i > 0 ; i-- )
	    if ( this.data[i] != other.data[i] )
		break;
	// careful! want unsigned compare!
	// use brute force here.
	int a = this.data[i];
	int b = other.data[i];
	if ( a < 0 ){
	    // a is really big, unsigned
	    if ( b < 0 ){
		return a-b; // both big, negative
	    } else {
		return 1; // b not big, answer is obvious;
	    }
	} else {
	    // a is not really big
	    if ( b < 0 ) {
		// but b is really big
		return -1;
	    } else {
		return a - b;
	    }
	}
    }

    /*
     * Compute
     * q = (int)( this / S )
     * this = 10 * ( this mod S )
     * Return q.
     * This is the iteration step of digit development for output.
     * We assume that S has been normalized, as above, and that
     * "this" has been lshift'ed accordingly.
     * Also assume, of course, that the result, q, can be expressed
     * as an integer, 0 <= q < 10.
     */
    public int
    quoRemIteration( FDBigInt S )throws IllegalArgumentException {
	// ensure that this and S have the same number of
	// digits. If S is properly normalized and q < 10 then
	// this must be so.
	if ( nWords != S.nWords ){
	    throw new IllegalArgumentException("disparate values");
	}
	// estimate q the obvious way. We will usually be
	// right. If not, then we're only off by a little and
	// will re-add.
	int n = nWords-1;
	long q = ((long)data[n]&0xffffffffL) / (long)S.data[n];
	long diff = 0L;
	for ( int i = 0; i <= n ; i++ ){
	    diff += ((long)data[i]&0xffffffffL) -  q*((long)S.data[i]&0xffffffffL);
	    data[i] = (int)diff;
	    diff >>= 32; // N.B. SIGNED shift.
	}
	if ( diff != 0L ) {
	    // damn, damn, damn. q is too big.
	    // add S back in until this turns +. This should
	    // not be very many times!
	    long sum = 0L;
	    while ( sum ==  0L ){
		sum = 0L;
		for ( int i = 0; i <= n; i++ ){
		    sum += ((long)data[i]&0xffffffffL) +  ((long)S.data[i]&0xffffffffL);
		    data[i] = (int) sum;
		    sum >>= 32; // Signed or unsigned, answer is 0 or 1
		}
		/*
		 * Originally the following line read
		 * "if ( sum !=0 && sum != -1 )"
		 * but that would be wrong, because of the
		 * treatment of the two values as entirely unsigned,
		 * it would be impossible for a carry-out to be interpreted
		 * as -1 -- it would have to be a single-bit carry-out, or
		 * +1.
		 */
		if ( sum !=0 && sum != 1 )
		    throw new RuntimeException("Assertion botch: "+sum+" carry out of division correction");
		q -= 1;
	    }
	}
	// finally, we can multiply this by 10.
	// it cannot overflow, right, as the high-order word has
	// at least 4 high-order zeros!
	long p = 0L;
	for ( int i = 0; i <= n; i++ ){
	    p += 10*((long)data[i]&0xffffffffL);
	    data[i] = (int)p;
	    p >>= 32; // SIGNED shift.
	}
	if ( p != 0L )
	    throw new RuntimeException("Assertion botch: carry out of *10");

	return (int)q;
    }

    public long
    longValue(){
	// if this can be represented as a long,
	// return the value
	int i;
	for ( i = this.nWords-1; i > 1 ; i-- ){
	    if ( data[i] != 0 ){
		throw new RuntimeException("Assertion botch: value too big");
	    }
	}
	switch(i){
	case 1:
	    if ( data[1] < 0 )
		throw new RuntimeException("Assertion botch: value too big");
	    return ((long)(data[1]) << 32) | ((long)data[0]&0xffffffffL);
	case 0:
	    return ((long)data[0]&0xffffffffL);
	default:
	    throw new RuntimeException("Assertion botch: longValue confused");
	}
    }

    public String
    toString() {
	StringBuffer r = new StringBuffer(30);
	r.append('[');
	int i = Math.min( nWords-1, data.length-1) ;
	if ( nWords > data.length ){
	    r.append( "("+data.length+"<"+nWords+"!)" );
	}
	for( ; i> 0 ; i-- ){
	    r.append( Integer.toHexString( data[i] ) );
	    r.append( (char) ' ' );
	}
	r.append( Integer.toHexString( data[0] ) );
	r.append( (char) ']' );
	return new String( r );
    }
}