pio2_1t
pio2_1t = 2.0222662487959507323996846200947577e-21L, /* 0x13198a2e03707344a4093822299f3.0p-181 */
w = fn*pio2_1t; /* 1st round good to 180 bit */
pio2_1t = -1.07463465549719416346e-12L, /* -0x973dcb3b399d747f.0p-103 */
w = fn*pio2_1t; /* 1st round good to 102 bit */
y[1] = (z-y[0])-3*pio2_1t;
y[0] = z + 3*pio2_1t;
y[1] = (z-y[0])+3*pio2_1t;
y[0] = z - 4*pio2_1t;
y[1] = (z-y[0])-4*pio2_1t;
y[0] = z + 4*pio2_1t;
y[1] = (z-y[0])+4*pio2_1t;
w = fn*pio2_1t; /* 1st round good to 85 bit */
pio2_1t = 6.07710050650619224932e-11, /* 0x3DD0B461, 0x1A626331 */
y[0] = z - pio2_1t;
y[1] = (z-y[0])-pio2_1t;
y[0] = z + pio2_1t;
y[1] = (z-y[0])+pio2_1t;
y[0] = z - 2*pio2_1t;
y[1] = (z-y[0])-2*pio2_1t;
y[0] = z + 2*pio2_1t;
y[1] = (z-y[0])+2*pio2_1t;
y[0] = z - 3*pio2_1t;
pio2_1t = 1.58932547735281966916e-08; /* 0x3E5110b4, 0x611A6263 */
w = fn*pio2_1t;