result of acos is never more precise than double

20 largest ulp errors (stored in a double)
   0.50242 ulp for acos(0.99219766722932401) = 0.125000000000040468)
   0.50037 ulp for acos(0.91057774319996676) = 0.4261166593349478)
   0.50035 ulp for acos(0.992197667223120305) = 0.125000000049799581)
   0.50033 ulp for acos(0.910577743200102319) = 0.426116659334619841)
   0.50031 ulp for acos(0.782890517800007291) = 0.671498051386918426)
   0.50028 ulp for acos(0.71077356760004895) = 0.780199005305909798)
   0.50028 ulp for acos(-0.479878203800012559) = 2.07131220875440025)
   0.50027 ulp for acos(-0.280154108799988755) = 1.85475096976218579)
   0.50027 ulp for acos(0.213887689999990721) = 1.35524329976689195)
   0.50025 ulp for acos(-0.795485219800061261) = 2.49060421440965651)
   0.50024 ulp for acos(0.443226369600003778) = 1.11160162948930052)
   0.50024 ulp for acos(0.479282989400335424) = 1.07095875354136449)
   0.50023 ulp for acos(-0.477825138199994948) = 2.06897358675603105)
   0.50022 ulp for acos(-0.174831552799988993) = 1.74653101021325785)
   0.50022 ulp for acos(-0.500124640400019027) = 2.09453903071070791)
   0.50022 ulp for acos(-0.888571940199981758) = 2.6650190254711239)
   0.50021 ulp for acos(-0.193720938600005499) = 1.7657498497942683)
   0.50021 ulp for acos(0.36701231999999967) = 1.19500116212440188)
   0.50021 ulp for acos(-0.767191877399947875) = 2.44524794743638285)
   0.50020 ulp for acos(0.0270132234000022911) = 1.54377981699332922)

<tr><td align=left><a href=acos.res>acos</a></td><td align=right>1308</td><td align=right>0.50242</td><td>0.99219766722932401</td><td>0.125000000000040468</td></tr>