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)
   0.51485 ulp for pow2_x(-1019.02662636594437) = 1.74750764179756589e-307)
   0.51444 ulp for pow2_x(-1016.07393710087092) = 1.35290443432495107e-306)
   0.51428 ulp for pow2_x(-1019.02662636853699) = 1.74750763865716706e-307)
   0.51415 ulp for pow2_x(0.741966908099998435) = 1.67245443736885946)
   0.51255 ulp for pow2_x(1018.90996795595413) = 5.27792525789884481e+306)
   0.51107 ulp for pow2_x(1013.8624620028761) = 1.59592523018360556e+305)
   0.51103 ulp for pow2_x(-1019.22318214739676) = 1.52492996187958852e-307)
   0.51096 ulp for pow2_x(-1018.43343033168856) = 2.63626390350783076e-307)
   0.51031 ulp for pow2_x(0.598293376600001037) = 1.51392462303024811)
   0.51023 ulp for pow2_x(349.987535962184154) = 2.27376948176768487e+105)
   0.51013 ulp for pow2_x(1017.74542579475599) = 2.35451311586518596e+306)
   0.51002 ulp for pow2_x(331.716190080000217) = 7.18659649823452515e+99)
   0.50979 ulp for pow2_x(6.78795284350002426) = 110.503851465954483)
   0.50971 ulp for pow2_x(331.716190077661508) = 7.18659648658455349e+99)
   0.50946 ulp for pow2_x(-9.16850938049999442) = 0.00173781547783360924)
   0.50911 ulp for pow2_x(-1013.28529304243034) = 9.34829974172118964e-306)
   0.50873 ulp for pow2_x(8.03471922500001945) = 262.235505875342881)
   0.50855 ulp for pow2_x(-1013.65138603404057) = 7.25316667310440613e-306)
   0.50852 ulp for pow2_x(0.675383053800000965) = 1.59702074565432395)
   0.50851 ulp for pow2_x(-9.73891256910015635) = 0.00117029457425831592)

<tr><td align=left><a href=pow2_x.res>pow2_x</a></td><td align=right>1467</td><td align=right>0.51485</td><td>-1019.02662636594437</td><td>1.74750764179756589e-307</td></tr>