linux-kernel - Re: [patch] crypto: sha256-mb - cleanup a || vs

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Date:	Fri, 1 Jul 2016 09:55:59 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Megha Dey <megha.dey@...el.com>,
	"Wang, Rui Y" <rui.y.wang@...el.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Xiaodong Liu <xiaodong.liu@...el.com>,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [patch] crypto: sha256-mb - cleanup a || vs | typo


* Tim Chen <tim.c.chen@...ux.intel.com> wrote:

> On Wed, 2016-06-29 at 10:05 -0700, H. Peter Anvin wrote:
> > On 06/29/16 07:42, Dan Carpenter wrote:
> > > 
> > > > 
> > > > > 
> > > > > and | behave basically the same here but || is intended.  It causes a
> > > static checker warning to mix up bitwise and logical operations.
> > > 
> > > Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> > > 
> > > diff --git a/arch/x86/crypto/sha256-mb/sha256_mb.c b/arch/x86/crypto/sha256-mb/sha256_mb.c
> > > index c9d5dcc..4ec895a 100644
> > > --- a/arch/x86/crypto/sha256-mb/sha256_mb.c
> > > +++ b/arch/x86/crypto/sha256-mb/sha256_mb.c
> > > @@ -299,7 +299,7 @@ static struct sha256_hash_ctx *sha256_ctx_mgr_submit(struct sha256_ctx_mgr *mgr,
> > >  	 * Or if the user's buffer contains less than a whole block,
> > >  	 * append as much as possible to the extra block.
> > >  	 */
> > > -	if ((ctx->partial_block_buffer_length) | (len < SHA256_BLOCK_SIZE)) {
> > > +	if ((ctx->partial_block_buffer_length) || (len < SHA256_BLOCK_SIZE)) {
> > >  		/* Compute how many bytes to copy from user buffer into
> > >  		 * extra block
> > >  		 */
> > > 
> > As far as I know the | was an intentional optimization, so you may way
> > to look at the generated code.
> > 
> > 	-hpa
> > 
> 
> Yes, this is an intentional optimization. [...]

Please don't do intentional optimizations while mixing them with a very ugly 
coding style:

	if ((ctx->partial_block_buffer_length) | (len < SHA256_BLOCK_SIZE)) {

The extra, unnecessary parantheses around ctx->partial_block_buffer_length will 
make the ordinary reader assume that the person who wrote the code was unsure 
about basic C syntax details and typoed the '|' as well ...

Also, for heaven's (and readability's) sake, pick shorter structure field names. 
What's wrong with ctx->partial_block_buf_len?

Also, even if the '|' was intentional - wouldn't it result in better code to use 
'||'?

Plus:

> > >  		/* Compute how many bytes to copy from user buffer into
> > >  		 * extra block
> > >  		 */

please use the customary (multi-line) comment style:

  /*
   * Comment .....
   * ...... goes here.
   */

specified in Documentation/CodingStyle.

Thanks,

        Ingo