perl -MData::IEEE754::Tools=:all -le"$,=qq(\t); map { print $_, ulp($_) } @ARGV" 0.25 0.4 0.5 0.6 0.9 1 1.9 2

0.25    5.55111512312578e-017
0.4     5.55111512312578e-017
0.5     1.11022302462516e-016
0.6     1.11022302462516e-016
0.9     1.11022302462516e-016
1       2.22044604925031e-016
1.9     2.22044604925031e-016
2       4.44089209850063e-016