result of acos is never more precise than double

20 largest ulp errors (stored in a double)
   0.51853 ulp for acos(0.87853474179999769) = 0.49801029020727455)
   0.51553 ulp for acos(0.52708713979999888) = 1.0156270750354917)
   0.51512 ulp for acos(0.66053110759999811) = 0.8492703956847355)
   0.51450 ulp for acos(0.80688201139999849) = 0.63194175424421639)
   0.51191 ulp for acos(-0.58693407620000071) = 2.198063147619874)
   0.51143 ulp for acos(-0.50053783680000175) = 2.0950162542550794)
   0.51110 ulp for acos(-0.68283809919999938) = 2.3224367191423392)
   0.51050 ulp for acos(0.74706767740000291) = 0.72715643027096066)
   0.51018 ulp for acos(0.87758256189037398) = 0.49999999999999734)
   0.50962 ulp for acos(0.54030230586813977) = 1)
   0.50953 ulp for acos(0.62162282299999971) = 0.8999835894658037)
   0.50867 ulp for acos(0.44428752140000077) = 1.1104175026763037)
   0.50826 ulp for acos(0.74088277259999669) = 0.73641255468147138)
   0.50687 ulp for acos(-0.50081992140000087) = 2.095342125115625)
   0.50664 ulp for acos(0.52708713979999133) = 1.0156270750355005)
   0.50612 ulp for acos(0.68611433479999917) = 0.81466198725240879)
   0.50552 ulp for acos(0.82145767919999646) = 0.60683387041871206)
   0.50493 ulp for acos(0.55712805300000057) = 0.97987295477008785)
   0.50475 ulp for acos(-0.64845310760000063) = 2.2763469701368519)
   0.50427 ulp for acos(0.43239467219999828) = 1.1236494594242337)

<tr><td align=left><a href=acos.res>acos</a></td><td align=right>1308</td><td align=right>0.51853</td><td>0.87853474179999769</td><td>0.49801029020727455</td></tr>