Re: highest bit, statically determined

[kalvin.news@gmail.com]

maanantai, 1. lokakuuta 2012 11.52.43 UTC+3 Anatoly Chernyshev kirjoitti:
> > 
> 
> >     68580000 1.687923000
> 
> > 
> 
> >     68580000 1.447859000
> 
> > 
> 
> >     68580000 24.481472000
> 
> 
> 
> Yes, that could be expected. Here's the draft lightning-fast version:
> 
> 
> 
> procedure xx is
> 
> last_bit_a: array(0..255) of natural:=(0|1=>0,2|3=>1,4..7=>2, 8..15=>3, 16..31=>4,32..63=>5, 64..127=>6, 128..255=>7);
> 
> N:natural;
> 
> begin
> 
> ...
> 
> Highest_Bit_In_Octet:=last_bit_a(N);
> 
> ...
> 
> end xx;

This can be optimised for improved size so that we create a lookup table only for a nibble values (0..15), and divide the handling into two parts according to whether the higher nibble is zero or non-zero. The end result would be a slighter slower execution speed but less code space. And this method can easily be extended to larger data sizes, too.

- Kalvin