It depends, you could use the emulated version float_half_even/2 to
generate the test cases. I posted it somewhere on discourse SWI-Prolog.
Actually I posted two version now, one with ulp/1 and one with nexttoward/2.
But I didn’t do a re-validation yet against case/3, case2/3 and case3/3 with
the SWI-Prolog version of float_half_even/2.
Edit 13.10.2022
This seems to work:
emulatorswi.p.log (2,3 KB)
It can be used to find test cases:
?- case3(N, X, Y), float_half_even(X,Z), Y =\= Z.
false.
?- repeat, L is -(1<<57), H is (1<<57)+1, random(L, H, X), Z is X<<43,
float_half_even(Z, Y), Y =\= float(Z).
Z = -374221666956444521791366365184;
Z = 459815319774385442098847416320;
Etc..