svn commit: r299751 - head/sys/dev/bwn

[Conrad Meyer]

On Sat, May 14, 2016 at 12:52 PM, Adrian Chadd <adrian at freebsd.org> wrote:
> Author: adrian
> Date: Sat May 14 19:52:04 2016
> New Revision: 299751
> URL: https://svnweb.freebsd.org/changeset/base/299751
>
> Log:
>   [bwn] migrate sqrt and add another couple of util routines.
>
> ...
>
> +unsigned int
> +bwn_sqrt(struct bwn_mac *mac, unsigned int x)
> +{
> +       /* Table holding (10 * sqrt(x)) for x between 1 and 256. */
> +       static uint8_t sqrt_table[256] = {
> +               10, 14, 17, 20, 22, 24, 26, 28,
> ...
> +       };
> +
> +       if (x == 0)
> +               return (0);
> +       if (x >= 256) {
> +               unsigned int tmp;
> +
> +               for (tmp = 0; x >= (2 * tmp) + 1; x -= (2 * tmp++) + 1)
> +                       /* do nothing */ ;
> +               return (tmp);

Does this approximation method have a name?

> +       }
> +       return (sqrt_table[x - 1] / 10);

Why do we store the table as 10*sqrt() if we're just going to divide
every entry by ten?

Best,
Conrad