: ( a b step -- range )
>r over - r>
[ /i ] keep
range boa ; inline
:: nsieve ( n -- pi(n) )
[let | xs [ n [ 1 ] B{ } replicate-as ] |
0 0 xs set-nth-unsafe
0 1 xs set-nth-unsafe
xs [ swap 1 = [| i | i 2 * n 1 - i [ 0 swap xs set-nth-unsafe ] each i ] when drop ] each-index
xs 0 [ + ] reduce ] ;