Re: [PATCH 5/7] lib: rework bitmap_parse()

[Andy Shevchenko]

On Sun, Sep 08, 2019 at 08:30:19PM -0700, Yury Norov wrote:
> bitmap_parse() is ineffective and full of opaque variables and opencoded
> parts. It leads to hard understanding and usage of it. This rework
> includes:
>  - remove bitmap_shift_left() call from the cycle. Now it makes the
>    complexity of the algorithm as O(nbits^2). In the suggested approach
>    the input string is parsed in reverse direction, so no shifts needed;
>  - relax requirement on a single comma and no white spaces between chunks.
>    It is considered useful in scripting, and it aligns with
>    bitmap_parselist();
>  - split bitmap_parse() to small readable helpers;
>  - make an explicit calculation of the end of input line at the
>    beginning, so users of the bitmap_parse() won't bother doing this.

> +static const char *bitmap_get_x32_reverse(const char *start,
> +					const char *end, u32 *num)
> +{
> +	u32 ret = 0;
> +	int c, i;
> +

> +	if (!isxdigit(*end))
> +		return ERR_PTR(-EINVAL);

This seems redundant...

> +
> +	for (i = 0; i < 32; i += 4) {

> +		c = hex_to_bin(*end--);
> +		if (c < 0)
> +			return ERR_PTR(-EINVAL);

...because this will do the same check.

Am I right?

> +
> +		ret |= c << i;
> +
> +		if (start > end || __end_of_region(*end))
> +			goto out;
> +	}
> +

> +	if (isxdigit(*end))
> +		return ERR_PTR(-EOVERFLOW);

hex_to_bin() doesn't rely on ctype array, won't drain caches.
I guess it's not a fast path, so, either will work.

> +out:
> +	*num = ret;
> +	return end;
> +}

-- 
With Best Regards,
Andy Shevchenko