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From: "George Spelvin" <linux@sciencehorizons.net>
To: linux@sciencehorizons.net, phdm@macq.eu
Cc: geert@linux-m68k.org, gerg@linux-m68k.org,
	linux-kernel@vger.kernel.org, linux-m68k@vger.kernel.org,
	tglx@linutronix.de, torvalds@linux-foundation.org
Subject: Re: [PATCH 08/10] m68k: Add <asm/archhash.h>
Date: 25 May 2016 05:14:35 -0400	[thread overview]
Message-ID: <20160525091435.9218.qmail@ns.sciencehorizons.net> (raw)
In-Reply-To: <20160525085653.GA9917@frolo.macqel>

> On Wed, May 25, 2016 at 03:34:55AM -0400, George Spelvin wrote:
>> +static inline u32 __attribute_const__ __hash_32(u32 x)
>> +{
>> +	u32 a, b;
>> +
>> +	asm(   "move.l %2,%0"	/* 0x0001 */
>> +	"\n	lsl.l #2,%0"	/* 0x0004 */
>> +	"\n	move.l %0,%1"
>> +	"\n	lsl.l #7,%0"	/* 0x0200 */
>> +	"\n	add.l %2,%0"	/* 0x0201 */
>> +	"\n	add.l %0,%1"	/* 0x0205 */
>> +	"\n	add.l %0,%0"	/* 0x0402 */
>> +	"\n	add.l %0,%1"	/* 0x0607 */
>> +	"\n	lsl.l #5,%0"	/* 0x8040 */
>> +				/* 0x8647 */

> There is no standard way to write asm in the kernel, but I prefer
> a simple semicolon after each insn

I did it the way I did above because it makes the gcc -S output very
legible.  Just like I put a space before the perands on m68k but a tab
on h8300: that's what GCC does on those platforms.

I started with the "\n\t" suffixes on each line like so much other
kernel code, but then figured out the format above which is legible
both in C source and compiler output.

>>	asm("move.l	%2,%0;"	/* 0x0001 */
>>	    "lsl.l	#2,%0;"	/* 0x0004 */
>>	    "move.l	%0,%1;"
>>	    "lsl.l	#7,%0;"	/* 0x0200 */
>>	    "add.l	%2,%0;"	/* 0x0201 */
>>	    "add.l	%0,%1;"	/* 0x0205 */
>>	    "add.l	%0,%0;"	/* 0x0402 */
>>	    "add.l	%0,%1;"	/* 0x0607 */
>>	    "lsl.l	#5,%0"	/* 0x8040 */
>>				/* 0x8647 */

> Also, it took me some time to understand the hexadecimal constants
> in the comments (and the last one predicts a future event :)).


Can you recmmend a better way to comment this?  My nose is so deep
in the code it's hard for me to judge.

> Just my two cents

And thank you very much for them!

  reply	other threads:[~2016-05-25  9:14 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CA+55aFxPSW+84KfQ1N_WmND-wtvgj2zQm8nFPkRcc+gyU=uing@mail.gmail.com>
2016-05-25  7:20 ` [PATCH 00/10] String hash improvements George Spelvin
2016-05-25  8:00   ` Geert Uytterhoeven
2016-05-25  8:11     ` George Spelvin
2016-05-25  8:50       ` Geert Uytterhoeven
2016-05-25  9:07         ` George Spelvin
2016-05-25 16:08   ` Linus Torvalds
2016-05-28 19:57     ` [PATCH v3 " George Spelvin
2016-05-28 19:57       ` [PATCH v3 01/10] Pull out string hash to <linux/stringhash.h> George Spelvin
2016-05-28 19:57       ` [PATCH v3 02/10] fs/namei.c: Add hashlen_string() function George Spelvin
2016-05-28 19:57       ` [PATCH v3 03/10] <linux/sunrpc/svcauth.h>: Define hash_str() in terms of hashlen_string() George Spelvin
2016-05-28 19:57       ` [PATCH v3 04/10] Change hash_64() return value to 32 bits George Spelvin
2016-05-28 19:57       ` [PATCH v3 05/10] Eliminate bad hash multipliers from hash_32() and hash_64() George Spelvin
2016-05-28 19:57       ` [PATCH v3 06/10] fs/namei.c: Improve dcache hash function George Spelvin
2016-05-30 15:11         ` Peter Zijlstra
2016-05-30 16:06           ` George Spelvin
2016-05-30 16:27             ` Peter Zijlstra
2016-05-30 18:10               ` George Spelvin
2016-06-02  1:18                 ` Linus Torvalds
2016-06-02  2:31                   ` George Spelvin
2016-06-02 16:35                     ` Linus Torvalds
2016-06-02 18:23                       ` George Spelvin
2016-05-28 19:57       ` [PATCH v3 07/10] <linux/hash.h>: Add support for architecture-specific functions George Spelvin
2016-05-29  7:57         ` Geert Uytterhoeven
2016-05-28 19:57       ` [PATCH v3 08/10] m68k: Add <asm/hash.h> George Spelvin
2016-05-28 19:57       ` [PATCH v3 09/10] microblaze: " George Spelvin
2016-05-28 19:57       ` [PATCH v3 10/10] h8300: " George Spelvin
2016-05-28 20:47       ` [PATCH v3 00/10] String hash improvements Linus Torvalds
2016-05-28 20:54         ` George Spelvin
2016-06-02 22:59     ` [PATCH " Fubo Chen
2016-05-26 17:09   ` [PATCH v2 " George Spelvin
2016-05-25  7:21 ` [PATCH 01/10] Pull out string hash to <linux/stringhash.h> George Spelvin
2016-05-25  7:22 ` [PATCH 02/10] fs/namei.c: Add hash_string() function George Spelvin
2016-05-25  7:26 ` [PATCH 03/10] <linux/sunrpc/svcauth.h>: Define hash_str() in terms of hash_string() George Spelvin
2016-05-25  7:28 ` [PATCH 04/10] Change hash_64() return value to 32 bits George Spelvin
2016-05-25  7:29 ` [PATCH 05/10] Eliminate bad hash multipliers from hash_32() and hash_64() George Spelvin
2016-05-25  7:31 ` [PATCH 06/10] fs/namei.c: Improve dcache hash function George Spelvin
2016-05-25  7:33 ` [PATCH 07/10] <linux/hash.h>: Add support for architecture-specific functions George Spelvin
2016-05-26 17:16   ` [PATCH v2 " George Spelvin
2016-05-25  7:34 ` [PATCH 08/10] m68k: Add <asm/archhash.h> George Spelvin
2016-05-25  7:34 ` George Spelvin
2016-05-25  8:07   ` Geert Uytterhoeven
2016-05-25  8:19     ` George Spelvin
2016-05-25  8:24     ` [PATCH 08v2/10] " George Spelvin
2016-05-25  8:48       ` Geert Uytterhoeven
2016-05-25  8:56   ` [PATCH 08/10] " Philippe De Muyter
2016-05-25  9:14     ` George Spelvin [this message]
2016-05-25  9:31       ` Andreas Schwab
2016-05-25  9:51       ` Philippe De Muyter
2016-05-25 13:24   ` Philippe De Muyter
2016-05-25 13:42     ` George Spelvin
2016-05-26 17:19   ` [PATCH v2 08/10] m68k: Add <asm/hash.h> George Spelvin
2016-05-25  7:37 ` [PATCH 09/10] microblaze: Add <asm/archhash.h> George Spelvin
2016-05-26 17:21   ` [PATCH v2 09/10] microblaze: Add <asm/hash.h> George Spelvin
2016-05-25  7:38 ` [PATCH 10/10] h8300: Add <asm/archhash.h> George Spelvin
2016-05-26 17:23   ` [PATCH v2 10/10] h8300: Add <asm/hash.h> George Spelvin

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