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Message-ID: <1464952643.1767.42.camel@linux.intel.com>
Date: Fri, 03 Jun 2016 14:17:23 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: George Spelvin <linux@...encehorizons.net>
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
tytso@....edu
Subject: Re: [PATCH] lib/uuid.c: eliminate uuid_[bl]e_index arrays
On Tue, 2016-05-31 at 16:31 -0400, George Spelvin wrote:
> From a0d084b1225f2efcf4b5c81871c9c446155b9b13 Mon Sep 17 00:00:00 2001
> From: George Spelvin <linux@...encehorizons.net>
> Date: Tue, 31 May 2016 16:00:22 -0400
> Subject: [PATCH] lib/uuid.c: eliminate uuid_[bl]e_index arrays
There is a tool called git send-email. It would be better to use it
directly.
Also, please fix Cc list (I got bounce response) and add some key people
like Rasmus.
>
> Both input and output code is simplified if we instead use a mapping
> from binary UUID index to ASCII UUID position. This lets us combine
> hyphen-skipping and endian-swapping into one table.
>
> uuid_[bl]e_index were EXPORT_SYMBOLed for no obvious reason; there
> are no users outside of lib/. The replacement uuid_[bl]e_pos arrays
> are not exported pending finding a need.
>
> The arrays are combined in one contiguous uuid_byte_pos[2][16]
> array as a micro-optimization for uuid_string().
Oh, it makes readability worse.
> Choosing between
> the two can be done by adding 16 rather than loading a second
> full-word address.
>
> x86-64 code size reductions:
> uuid_string: was 228 bytes, now 134
> __uuid_to_bin: was 119 bytes, now 85
x86_32? arm?
> Initialized data is also reduced by 16 bytes.
> Here's a patch implementing the suggestion I made earlier. This
> reduces
> code size, data size, and run time for input and output of UUIDs.
>
> This patch is on top of the upper/lower case hex optimization for
> lib/vsprintf.c I sent earlier. If you don't have it, just ignore the
> merge conflicts in uuid_string() and take the "after" version.
>
--- a/include/linux/uuid.h
> +++ b/include/linux/uuid.h
> @@ -41,8 +41,10 @@ extern void uuid_be_gen(uuid_be *u);
>
> bool __must_check uuid_is_valid(const char *uuid);
>
> -extern const u8 uuid_le_index[16];
> -extern const u8 uuid_be_index[16];
> +/* For each binary byte, string offset in ASCII UUID where it appears
> */
> +extern const u8 uuid_byte_pos[2][16];
> +#define uuid_be_pos (uuid_byte_pos[0])
> +#define uuid_le_pos (uuid_byte_pos[1])
>
> int uuid_le_to_bin(const char *uuid, uuid_le *u);
> int uuid_be_to_bin(const char *uuid, uuid_be *u);
> diff --git a/lib/uuid.c b/lib/uuid.c
> index e116ae5f..8a439caf 100644
> --- a/lib/uuid.c
> +++ b/lib/uuid.c
> @@ -21,10 +21,10 @@
> #include <linux/uuid.h>
> #include <linux/random.h>
>
> -const u8 uuid_le_index[16] = {3,2,1,0,5,4,7,6,8,9,10,11,12,13,14,15};
> -EXPORT_SYMBOL(uuid_le_index);
> -const u8 uuid_be_index[16] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
> -EXPORT_SYMBOL(uuid_be_index);
> +const u8 uuid_byte_pos[2][16] = {
> + {0,2,4,6,9,11,14,16,19,21,24,26,28,30,32,34}, /*
> uuid_be_pos */
> + {6,4,2,0,11,9,16,14,19,21,24,26,28,30,32,34} /*
> uuid_le_pos */
> +};
And what prevent you to use two arrays? Above looks not good for reading
and error prone for users.
>
> /***************************************************************
> * Random UUID interface
> @@ -97,32 +97,28 @@ bool uuid_is_valid(const char *uuid)
> }
> EXPORT_SYMBOL(uuid_is_valid);
>
> -static int __uuid_to_bin(const char *uuid, __u8 b[16], const u8
> ei[16])
> +static int __uuid_to_bin(const char uuid[36], __u8 b[16], const u8
> si[16])
This one... Let's keep a prototype as is for now.
> {
> - static const u8 si[16] =
> {0,2,4,6,9,11,14,16,19,21,24,26,28,30,32,34};
> unsigned int i;
>
> if (!uuid_is_valid(uuid))
> return -EINVAL;
>
>
> - for (i = 0; i < 16; i++) {
> - int hi = hex_to_bin(uuid[si[i]] + 0);
> - int lo = hex_to_bin(uuid[si[i]] + 1);
> -
> - b[ei[i]] = (hi << 4) | lo;
> - }
> + for (i = 0; i < 16; i++)
> + if (hex2bin(b + i, uuid + si[i], 1) < 0)
> + return -EINVAL;
How hex2bin is better here? We have validation done, no need to repeat.
So, I suggest not to touch this piece of code.
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1313,38 +1313,32 @@ char *uuid_string(char *buf, char *end, const
> u8 *addr,
> struct printf_spec spec, const char *fmt)
> {
> char uuid[UUID_STRING_LEN + 1];
> - char *p = uuid;
> int i;
> - const u8 *index = uuid_be_index;
> + const u8 *pos = uuid_be_pos;
> const char *hex = hex_asc;
>
> switch (fmt[1]) {
> + case 'l':
> + pos = uuid_le_pos;
> + break;
> case 'L':
> - hex = hex_asc_upper; /* fall-through */
> - case 'l':
> - index = uuid_le_index;
> - break;
> + pos = uuid_le_pos; /* Fall-through */
> case 'B':
> hex = hex_asc_upper;
> break;
> }
>
> + /* Format each byte of the raw uuid into the buffer */
> for (i = 0; i < 16; i++) {
> - u8 byte = addr[index[i]];
> + u8 byte = addr[i];
> + char *p = uuid + pos[i];
>
> - *p++ = hex[byte >> 4];
> - *p++ = hex[byte & 0x0f];
> - switch (i) {
> - case 3:
> - case 5:
> - case 7:
> - case 9:
> - *p++ = '-';
> - break;
> - }
>
> + p[0] = hex[byte >> 4];
> + p[1] = hex[byte & 0x0f];
If you wish you may convert this to hex_byte_pack{,upper}().
--
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy
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