Re: [Caml-list] Counting bits in a big_int

[Yaron Minsky <yminsky@gmail.com>]

Nice.  The weird thing about the Nat module is that it's completely
undocumented.  Is there any reason to think it wil be stable between
revisions?  For instance, does Xavier's reimplementation have the same
Num module with the same interface as the previous one?

I guess my real question is: why is Nat undocumented?

y

On Sat, 15 May 2004 13:14:33 +0200, Markus Mottl <markus@oefai.at> wrote:
> 
> On Fri, 14 May 2004, Yaron Minsky wrote:
> > Here's the fastest bitcounter I've been able to come up with.  It's
> > about an order of magnitude faster than just counting bit by bit.
> 
> How about this:
> 
> ---------------------------------------------------------------------------
> open Big_int
> open Nat
> 
> let nbits x =
>  let nat = nat_of_big_int (abs_big_int x) in
>  let nwords = num_digits_nat nat 0 (length_nat nat) in
>  Sys.word_size * nwords - num_leading_zero_bits_in_digit nat (nwords - 1)
> ---------------------------------------------------------------------------
> 
> This runs another order of magnitude faster, and it's shorter, too :-)
> 
> Regards,
> Markus
> 
> --
> Markus Mottl          http://www.oefai.at/~markus          markus@oefai.at
>

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