result of pow2_x is never more precise than double

3 results were exact to double the precision

20 largest ulp errors (stored in a double)
   0.51301 ulp for pow2_x(7.7659010114999996) = 217.65525035386418)
   0.50849 ulp for pow2_x(342.72814748000013) = 1.4840644087240671e+103)
   0.50644 ulp for pow2_x(1022.67331979571) = 7.1671257396093824e+307)
   0.50600 ulp for pow2_x(1014.9519775860215) = 3.3961699260268462e+305)
   0.50558 ulp for pow2_x(-1016.0739370982216) = 1.3529044368094183e-306)
   0.50544 ulp for pow2_x(1014.3561666918408) = 2.2471520588624207e+305)
   0.50523 ulp for pow2_x(-9.0520129452000351) = 0.0018839639245156964)
   0.50515 ulp for pow2_x(1016.3888907950087) = 9.1948233268544662e+305)
   0.50438 ulp for pow2_x(1022.8883994526165) = 8.3193702335404877e+307)
   0.50438 ulp for pow2_x(-1017.0556631820348) = 6.8507500458144197e-307)
   0.50400 ulp for pow2_x(308.4546322599989) = 7.1465528832505223e+92)
   0.50382 ulp for pow2_x(5.5990533549998958) = 48.471114675739457)
   0.50313 ulp for pow2_x(-1019.0266263671789) = 1.74750764030221e-307)
   0.50306 ulp for pow2_x(457.55409682002147) = 5.4639634022362095e+137)
   0.50302 ulp for pow2_x(-1018.8030828633669) = 2.0403862264942608e-307)
   0.50289 ulp for pow2_x(7.2251346234999465) = 149.61744855201033)
   0.50285 ulp for pow2_x(1015.9780960839656) = 6.9164279770989944e+305)
   0.50273 ulp for pow2_x(1018.6323830568876) = 4.354134644958173e+306)
   0.50259 ulp for pow2_x(-9.3549015996999145) = 0.0015271933067628912)
   0.50250 ulp for pow2_x(-1020.6800991004802) = 5.5548737581214371e-308)

<tr><td align=left><a href=pow2_x.res>pow2_x</a></td><td align=right>1467</td><td align=right>0.51301</td><td>7.7659010114999996</td><td>217.65525035386418</td></tr>