Question

If two double values(a and b) which

1. both are not negative
2. both are not an NaN nor any (POSITIVE|NEGATIVE)_INFINITY,
3. a >= b

Is it always true that

1. Double.doubleToLongBits(a) >= Double.doubleToLongBits(b)

?

Is there any possible false per IEEE 754 stuff?

I’m intending to store a rate value for two positive (non-zero) integers as a long value not as a double value.

@Entity
public class ExchangeRate {

    @PrePersist
    protected void prePersist() {
        targetAmountPerSourceAmount = Double.doubleToLongBits(
            (double) targetAmount / (double) sourceAmount);
    }

    @Basic
    private long targetAmountPerSourceAmount;

    @Min(1)
    @Max(Short.MAX_VALUE)
    private short targetAmount;

    @Min(1)
    @Max(Short.MAX_VALUE)
    private short sourceAmount;
}

Answer 1

Well, zeros are going to cause you a problem, since +0.0 == -0.0 but they have different representations.

    double a = -0.0;
    double b = +0.0;
    System.out.println("a == b? " + (a == b)); // true
    long aLong = Double.doubleToLongBits(a);
    long bLong = Double.doubleToLongBits(b);
    System.out.println("a' >= b'? " + (aLong >= bLong)); // false