Definition Bsign x :=
match x with
| B754_nan s _ => s
| B754_zero s => s
| B754_infinity s => s
| B754_finite s _ _ _ => s
end.
Definition sign_FF x :=
match x with
| F754_nan s _ => s
| F754_zero s => s
| F754_infinity s => s
| F754_finite s _ _ => s
end.

Theorem Bsign_FF2B :
forall x H,
Bsign (FF2B x H) = sign_FF x.