pio4
z = pio4 - x;
pio4 = 7.8539812565e-01, /* 0x3f490fda */
z = pio4-x;
pio4 = 0x1.921fb54442d18469898cc51701b8p-1L,
z = pio4 - x;
pio4 = 0.785398163397448309628L, /* 0xc90fdaa22168c235.0p-64 */
z = pio4 - x;