Re: [PATCH] b43: LP-PHY: Fix and simplify Qdiv roundup

[Michael Buesch <mb@bu3sch.de>]

On Tuesday 25 August 2009 16:40:17 Gábor Stefanik wrote:
> The Qdiv roundup routine is essentially a fixed-point
> division algorithm, using only integer math.
> However, the version in the specs had a major error
> that has been recently fixed (a missing quotient++).
> 
> Replace Qdiv roundup with a rewritten, simplified version.

Don't we have some sort of standard library function somewhere in
the kernel for this? If not, what about creating one?

> 
> Signed-off-by: Gábor Stefanik <netrolller.3d@gmail.com>
> ---
>  drivers/net/wireless/b43/phy_lp.c |   14 ++++----------
>  1 files changed, 4 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/net/wireless/b43/phy_lp.c b/drivers/net/wireless/b43/phy_lp.c
> index 7e70c07..d0280d5 100644
> --- a/drivers/net/wireless/b43/phy_lp.c
> +++ b/drivers/net/wireless/b43/phy_lp.c
> @@ -1034,7 +1034,7 @@ static int lpphy_loopback(struct b43_wldev *dev)
>  
>  static u32 lpphy_qdiv_roundup(u32 dividend, u32 divisor, u8 precision)
>  {
> -	u32 quotient, remainder, rbit, roundup, tmp;
> +	u32 quotient, remainder;
>  
>  	if (divisor == 0)
>  		return 0;
> @@ -1042,20 +1042,14 @@ static u32 lpphy_qdiv_roundup(u32 dividend, u32 divisor, u8 precision)
>  	quotient = dividend / divisor;
>  	remainder = dividend % divisor;
>  
> -	rbit = divisor & 0x1;
> -	roundup = (divisor >> 1) + rbit;
> -
>  	while (precision != 0) {
> -		tmp = remainder - roundup;
>  		quotient <<= 1;
> -		if (remainder >= roundup)
> -			remainder = (tmp << 1) + rbit;
> -		else
> -			remainder <<= 1;
> +		quotient |= (remainder << 1) / divisor;
> +		remainder = (remainder << 1) % divisor;
>  		precision--;
>  	}
>  
> -	if (remainder >= roundup)
> +	if (remainder << 1 >= divisor)
>  		quotient++;
>  
>  	return quotient;



-- 
Greetings, Michael.