Re: [PATCH 4/6] lib: rework bitmap_parse()

[Yury Norov]

On Sun, Apr 28, 2019 at 07:57:45PM +0300, Andy Shevchenko wrote:
> On Sat, Apr 27, 2019 at 08:29:34PM -0700, Yury Norov wrote:
> > bitmap_parse() is ineffective and full of opaque variables and opencoded
> > parts. It leads to hard understanding 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 inline bool in_str(const char *start, const char *ptr)
> > +{
> > +	return start <= ptr;
> > +}
> > +
> 
> I don't see how it's better than explicit use. Moreover, explicit use shows the
> exact condition in-line. Even by used characters it's longer.

I did 2 mistakes with a condition ('<' instead of '<=') during the
development, after that I decided to introduce it. I would prefer
keep it.
 
> > +static const char *bitmap_get_hex32_rev(const char *start,
> > +					const char *end, u32 *num)
> 
> In kernel few functions to work with hex u32 named foo_x32(). I would rather
> use that. Besides, we spell "reverse" in full.

OK

> > +{
> > +	u32 ret = 0;
> > +	int c, i;
> > +
> > +	if (hex_to_bin(*end) < 0)
> > +		return ERR_PTR(-EINVAL);
> > +
> > +	for (i = 0; i < 32; i += 4) {
> > +		c = hex_to_bin(*end--);
> > +		if (c < 0)
> 
> Perhaps we may need similar patch for hex_to_bin() as in the commit
> 9888a588ea96 ("lib/hexdump.c: return -EINVAL in case of error in hex2bin()")
> 
> > +			return ERR_PTR(-EINVAL);
> 
> > +
> > +		ret |= c << i;
> > +
> > +		if (!in_str(start, end) || __end_of_region(*end))
> > +			goto out;
> > +	}
> > +
> > +	if (hex_to_bin(*end) >= 0)
> > +		return ERR_PTR(-EOVERFLOW);
> > +out:
> > +	*num = ret;
> > +	return end;
> > +}
> 
> -- 
> With Best Regards,
> Andy Shevchenko
>