BigDecimal.movePointRight() 因数字非常大而挂起
下面的程序冻结了，我不知道为什么。
import java.math.*;
public class BigDec {
public static BigDecimal exp(double z) {
// Find e^z = e^intPart * e^fracPart.
return new BigDecimal(Math.E).pow((int)z, MathContext.DECIMAL128).
multiply(new BigDecimal(Math.exp(z-(int)z)), MathContext.DECIMAL128);
}
public static void main(String[] args) {
// This works OK:
BigDecimal x = new BigDecimal(3E200);
System.out.println("x=" + x);
System.out.println("x.movePointRight(1)=" + x.movePointRight(1));
// This does not:
x = exp(123456789);
System.out.println("x=" + x);
System.out.println("x.movePointRight(1)=" + x.movePointRight(1)); //hangs
}
}
就目前的目的而言，第一个方法只是创建一个非常大的 BigDecimal。 （详细信息：它找到 e 的 z 次方，即使它太大而无法成为双精度值。我很确定这个方法是正确的，尽管 MathContexts 可能不是在最好的位置。）
我知道 e^123456789 非常大，但我真的很想使用这样的数字。如有任何答复，我们将不胜感激。
The following program freezes, and I can't work out why.
import java.math.*;
public class BigDec {
public static BigDecimal exp(double z) {
// Find e^z = e^intPart * e^fracPart.
return new BigDecimal(Math.E).pow((int)z, MathContext.DECIMAL128).
multiply(new BigDecimal(Math.exp(z-(int)z)), MathContext.DECIMAL128);
}
public static void main(String[] args) {
// This works OK:
BigDecimal x = new BigDecimal(3E200);
System.out.println("x=" + x);
System.out.println("x.movePointRight(1)=" + x.movePointRight(1));
// This does not:
x = exp(123456789);
System.out.println("x=" + x);
System.out.println("x.movePointRight(1)=" + x.movePointRight(1)); //hangs
}
}
For the present purposes, the first method just creates a very large BigDecimal. (Details: it finds e to the power of z, even when this too large to be a double. I am pretty sure this method is correct, though the MathContexts may not be in the best places.)
I know e^123456789 is extremely big, but I really do want to use numbers like this. Any answers would be very gratefully received.
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事实上它不会冻结，但 Oracle VM 中
movePointRight的实现效率可能极低。使用 10 的幂进行乘法或除法通常比使用movePointRight或movePointLeft方法要快得多。在您的情况下，使用 x.multiply(BigDecimal.TEN) 可能会效果更好。In fact it does not freeze, but the implementation of
movePointRightin Oracle's VM can be extremely inefficient. It is often much faster to multiply or divide with a power of 10 instead of using themovePointRightormovePointLeftmethods. In your case, usingx.multiply(BigDecimal.TEN)will probably work much better.