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Subject: Re: highest bit, statically determined
From: kalvin.news@gmail.com
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Date: 2012-10-04T03:01:50-07:00
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maanantai, 1. lokakuuta 2012 11.52.43 UTC+3 Anatoly Chernyshev kirjoitti:
> >=20
>=20
> >     68580000 1.687923000
>=20
> >=20
>=20
> >     68580000 1.447859000
>=20
> >=20
>=20
> >     68580000 24.481472000
>=20
>=20
>=20
> Yes, that could be expected. Here's the draft lightning-fast version:
>=20
>=20
>=20
> procedure xx is
>=20
> last_bit_a: array(0..255) of natural:=3D(0|1=3D>0,2|3=3D>1,4..7=3D>2, 8..=
15=3D>3, 16..31=3D>4,32..63=3D>5, 64..127=3D>6, 128..255=3D>7);
>=20
> N:natural;
>=20
> begin
>=20
> ...
>=20
> Highest_Bit_In_Octet:=3Dlast_bit_a(N);
>=20
> ...
>=20
> end xx;

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

- Kalvin