private void test(
final BigDecimal valueToSplit, final int childrenCount, final MathContext mathContext) {
final String info =
"ValueToSplit="
+ valueToSplit
+ ", childrenCount="
+ childrenCount
+ ", mathContext="
+ mathContext;
final int precision = mathContext.getPrecision();
final BigDecimal splitValueExpected =
valueToSplit.divide(BigDecimal.valueOf(childrenCount), mathContext);
// Delta: tolerated difference between calculated split value and actual split value
// i.e. 1^(-precision) = 1/(1^precision) ... because BigDecimal does not support negative powers
final BigDecimal splitValueExpectedDelta = BigDecimal.ONE.divide(BigDecimal.ONE.pow(precision));
// Example: For ValueToSplit=100, childrenCount=33, precision=2
// splitValueExpected = 0.03
// splitValueExpectedDelta = 1^(-2) = 0.01
final MutableAttributeSplitRequest request = createRequest(valueToSplit, childrenCount);
BigDecimal splitValueSUM = BigDecimal.ZERO;
for (int index = 0; index < childrenCount; index++) {
//
// Update request current index
request.setAttributeStorageCurrent(request.getAttributeStorages().get(index));
request.setAttributeStorageCurrentIndex(index);
//
// Execute splitting
final IAttributeSplitResult result = splitter.split(request);
//
// Get and check split value
final BigDecimal splitValue = (BigDecimal) result.getSplitValue();
assertEquals(
"Invalid split value on index=" + index + "\n" + info,
splitValueExpected, // expected
splitValue, // actual
splitValueExpectedDelta // delta
);
//
// Update SUM of split values
splitValueSUM = splitValueSUM.add(splitValue);
//
// Update: request's ValueToSplit = last split remaining value
final BigDecimal remainingValue = (BigDecimal) result.getRemainingValue();
final BigDecimal remainingValueExpected = valueToSplit.subtract(splitValueSUM);
assertEquals(
"Invalid remaining value on index=" + index + "\n" + info,
remainingValueExpected, // expected
remainingValue, // actual
BigDecimal.ZERO // delta=exact
);
request.setValueToSplit(remainingValue);
}
//
// Assume: sum of all split values shall be the same as initial value to split
Assert.assertThat(
"Invalid splitValues SUM" + "\n" + info,
splitValueSUM, // actual
Matchers.comparesEqualTo(valueToSplit) // expected
);
}
public static BigDecimal sqrt(BigDecimal squarD, int scalar) {
// Static constants - perhaps initialize in class Vladimir!
BigDecimal TWO = new BigDecimal(2);
double SQRT_10 = 3.162277660168379332;
MathContext rootMC = new MathContext(scalar);
// General number and precision checking
int sign = squarD.signum();
if (sign == -1) throw new ArithmeticException("\nSquare root of a negative number: " + squarD);
else if (sign == 0) return squarD.round(rootMC);
int prec = rootMC.getPrecision(); // the requested precision
if (prec == 0)
throw new IllegalArgumentException("\nMost roots won't have infinite precision = 0");
// Initial precision is that of double numbers 2^63/2 ~ 4E18
int BITS = 62; // 63-1 an even number of number bits
int nInit = 16; // precision seems 16 to 18 digits
MathContext nMC = new MathContext(18, RoundingMode.HALF_UP);
// Iteration variables, for the square root x and the reciprocal v
BigDecimal x = null, e = null; // initial x: x0 ~ sqrt()
BigDecimal v = null, g = null; // initial v: v0 = 1/(2*x)
// Estimate the square root with the foremost 62 bits of squarD
BigInteger bi = squarD.unscaledValue(); // bi and scale are a tandem
int biLen = bi.bitLength();
int shift = Math.max(0, biLen - BITS + (biLen % 2 == 0 ? 0 : 1)); // even
// shift..
bi = bi.shiftRight(shift); // ..floors to 62 or 63 bit BigInteger
double root = Math.sqrt(bi.doubleValue());
BigDecimal halfBack = new BigDecimal(BigInteger.ONE.shiftLeft(shift / 2));
int scale = squarD.scale();
if (scale % 2 == 1) // add half scales of the root to odds..
root *= SQRT_10; // 5 -> 2, -5 -> -3 need half a scale more..
scale = (int) Math.floor(scale / 2.); // ..where 100 -> 10 shifts the
// scale
// Initial x - use double root - multiply by halfBack to unshift - set
// new scale
x = new BigDecimal(root, nMC);
x = x.multiply(halfBack, nMC); // x0 ~ sqrt()
if (scale != 0) x = x.movePointLeft(scale);
if (prec < nInit) // for prec 15 root x0 must surely be OK
return x.round(rootMC); // return small prec roots without
// iterations
// Initial v - the reciprocal
v = BigDecimal.ONE.divide(TWO.multiply(x), nMC); // v0 = 1/(2*x)
// Collect iteration precisions beforehand
ArrayList<Integer> nPrecs = new ArrayList<Integer>();
assert nInit > 3 : "Never ending loop!"; // assume nInit = 16 <= prec
// Let m be the exact digits precision in an earlier! loop
for (int m = prec + 1; m > nInit; m = m / 2 + (m > 100 ? 1 : 2)) nPrecs.add(m);
// The loop of "Square Root by Coupled Newton Iteration" for simpletons
for (int i = nPrecs.size() - 1; i > -1; i--) {
// Increase precision - next iteration supplies n exact digits
nMC =
new MathContext(
nPrecs.get(i), (i % 2 == 1) ? RoundingMode.HALF_UP : RoundingMode.HALF_DOWN);
// Next x // e = d - x^2
e = squarD.subtract(x.multiply(x, nMC), nMC);
if (i != 0) x = x.add(e.multiply(v, nMC)); // x += e*v ~ sqrt()
else {
x = x.add(e.multiply(v, rootMC), rootMC); // root x is ready!
break;
}
// Next v // g = 1 - 2*x*v
g = BigDecimal.ONE.subtract(TWO.multiply(x).multiply(v, nMC));
v = v.add(g.multiply(v, nMC)); // v += g*v ~ 1/2/sqrt()
}
return x; // return sqrt(squarD) with precision of rootMC
}