Paste: riced out

: <fast-range> ( a b step -- range )
    >r over - r>
    [ fixnum/i { fixnum } declare ] 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 <fast-range> [ 0 swap xs set-nth-unsafe ] each i ] when drop ] each-index 
    xs 0 [ + ] reduce ] ;