FSIGNIF
#define FMINEXP (-(FMAXEXP + FSIGNIF - _HIDDENBIT - 3))
#define FMAXPOWTWO ((float)(1 << (FSIGNIF - 1)))
(float)(FSIGNIF % 2 ? (1 << FSIGNIF/2) * M_SQRT2 : 1 << FSIGNIF/2)