From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Yury Norov <yury.norov@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Dmitry Torokhov <dmitry.torokhov@gmail.com>,
"David S . Miller" <davem@davemloft.net>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Amritha Nambiar <amritha.nambiar@intel.com>,
Willem de Bruijn <willemb@google.com>,
Kees Cook <keescook@chromium.org>,
Matthew Wilcox <willy@infradead.org>,
"Tobin C . Harding" <tobin@kernel.org>,
Will Deacon <will.deacon@arm.com>,
Miklos Szeredi <mszeredi@redhat.com>,
Vineet Gupta <vineet.gupta1@synopsys.com>,
Chris Wilson <chris@chris-wilson.co.uk>,
Arnaldo Carvalho de Melo <acme@redhat.com>,
linux-kernel@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
Steffen Klassert <steffen.klassert@secunet.com>
Subject: Re: [PATCH 5/7] lib: rework bitmap_parse()
Date: Mon, 9 Sep 2019 13:06:08 +0300 [thread overview]
Message-ID: <20190909100608.GR2680@smile.fi.intel.com> (raw)
In-Reply-To: <20190909033021.11600-6-yury.norov@gmail.com>
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
next prev parent reply other threads:[~2019-09-09 10:06 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-09 3:30 [PATCH v4 0/7] lib: rework bitmap_parse Yury Norov
2019-09-09 3:30 ` [PATCH 1/7] lib/string: add strnchrnul() Yury Norov
2019-09-09 3:30 ` [PATCH 2/7] bitops: more BITS_TO_* macros Yury Norov
2019-09-09 3:30 ` [PATCH 3/7] lib: add test for bitmap_parse() Yury Norov
2019-09-09 3:30 ` [PATCH 4/7] lib: make bitmap_parse_user a wrapper on bitmap_parse Yury Norov
2019-09-09 3:30 ` [PATCH 5/7] lib: rework bitmap_parse() Yury Norov
2019-09-09 10:06 ` Andy Shevchenko [this message]
2019-09-09 3:30 ` [PATCH 6/7] lib: new testcases for bitmap_parse{_user} Yury Norov
2019-09-09 3:30 ` [PATCH 7/7] cpumask: don't calculate length of the input string Yury Norov
-- strict thread matches above, loose matches on Subject: below --
2020-01-02 4:30 [PATCH v5 0/7] lib: rework bitmap_parse Yury Norov
2020-01-02 4:30 ` [PATCH 5/7] lib: rework bitmap_parse() Yury Norov
2019-07-21 21:27 [PATCH v3 0/7] lib: rework bitmap_parse Yury Norov
2019-07-21 21:27 ` [PATCH 5/7] lib: rework bitmap_parse() Yury Norov
2019-07-22 13:37 ` Andy Shevchenko
2019-05-01 1:06 [PATCH 0/7] lib: rework bitmap_parse Yury Norov
2019-05-01 1:06 ` [PATCH 5/7] lib: rework bitmap_parse() Yury Norov
2019-05-08 8:46 ` Andy Shevchenko
2019-05-10 2:26 ` Yury Norov
2019-05-24 2:51 ` Andrew Morton
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