sieve.mlton

[Doug Bagley]

Stephen Weeks wrote:
> 
> Here is a version of sieve that uses a bool array instead of a
> Word8Array.array and also has the nested loop in a more idiomatic style.  On my
> machine, it runs in about 65% of the time of your version, for reasons I don't
> understand.

Thanks I see the speedup too.

Recently I had noticed that on my machine, the programs that use char
arrays (like GCC) to represent booleans ran a lot faster than the ones
that use int arrays (which are larger and presumably don't fit into
the CPU cache).

So I recoded the Ocaml source to use a string instead of an bool array
(which I presume uses a full word to represent a boolean), and I got a
2.5x speedup.

Now the old SML programs were based on using lists to calculate the
sieve (I'd copied them from somewhere off the net) and were dreadfully
slow.  So I changed to emulate the Ocaml source and likewise use char
arrays.  That change made a dramatic speedup over the original, but I
should have checked bool arrays!  So thanks for checking up for me.

Cheers,
Doug