Value object equality & floating-point values

[Dan Smith]

> On Feb 12, 2024, at 6:54 PM, Joe Darcy <joe.darcy at oracle.com> wrote:
>> 
>> 
>> To put it simply, the spec *already allows* normalization (for the
>> very good reason that no Java developer should ever be exposed to
>> different NaNs).
> 
> The origin of that paragraph stems from idiosyncrasies of  64-bit double support on the x87 FPU -- tl;dr a format changing load/store instruction rather than a move instruction had to be used to get values on and off the floating-point stack. Fortunately, JEP 306: "Restore Always-Strict Floating-Point Semantics" removed most such issues from a spec perspective, which had not been a serious concern from an implementation perspective for some time.

Joe, does this imply that primitive floating-point data movement *in general* may not preserve NaN bits? E.g., the following assert may fail?

value class C {
    double d;
    C(double d) { this.d = d; }

    static double TMP;
}

double d1 = ...;
C.TMP = d1;
double d2 = C.TMP;
C c1 = new C(d1);
C c2 = new C(d2);
assert c1 == c2; // bitwise equivalence test