threads / patch / 20648

patchblock-sha1: make the size member first in the context struct

Subject: [PATCH] block-sha1: make the size member first in the context struct

## tl;dr

3 messages between Aug 18, 2009 and Aug 18, 2009. Diffs are folded; open one to read it.

replies: 2people: 2as markdown or json

Nicolas Pitre· Aug 18, 2009, 00:18 UTC · lore

This is a 64-bit value, hence having it first provides a better alignment.

Signed-off-by: Nicolas Pitre <nico@cam.org>

Show changes to block-sha1/sha1.h +1 −1

diff --git a/block-sha1/sha1.h b/block-sha1/sha1.h
index 6ff59b2..b864df6 100644
--- a/block-sha1/sha1.h
+++ b/block-sha1/sha1.h
@@ -7,9 +7,9 @@
  */
 
 typedef struct {
+	unsigned long long size;
 	unsigned int H[5];
 	unsigned int W[16];
-	unsigned long long size;
 } blk_SHA_CTX;
 
 void blk_SHA1_Init(blk_SHA_CTX *ctx);

Johannes Schindelin· Aug 18, 2009, 00:24 UTC · re: Nicolas Pitre · lore

Re: [PATCH] block-sha1: make the size member first in the context struct

Hi,

On Mon, 17 Aug 2009, Nicolas Pitre wrote:

Show 18 quoted lines

> This is a 64-bit value, hence having it first provides a better 
> alignment.
> 
> Signed-off-by: Nicolas Pitre <nico@cam.org>
> 
> diff --git a/block-sha1/sha1.h b/block-sha1/sha1.h
> index 6ff59b2..b864df6 100644
> --- a/block-sha1/sha1.h
> +++ b/block-sha1/sha1.h
> @@ -7,9 +7,9 @@
>   */
>  
>  typedef struct {
> +	unsigned long long size;
>  	unsigned int H[5];
>  	unsigned int W[16];
> -	unsigned long long size;
>  } blk_SHA_CTX;

By the reasoning suggested in the commit message, should H[5] not go to the end?

Ciao, Dscho

Nicolas Pitre· Aug 18, 2009, 00:39 UTC · re: Johannes Schindelin · lore

Re: [PATCH] block-sha1: make the size member first in the context struct

On Tue, 18 Aug 2009, Johannes Schindelin wrote:

Show 25 quoted lines

> Hi,
> 
> On Mon, 17 Aug 2009, Nicolas Pitre wrote:
> 
> > This is a 64-bit value, hence having it first provides a better 
> > alignment.
> > 
> > Signed-off-by: Nicolas Pitre <nico@cam.org>
> > 
> > diff --git a/block-sha1/sha1.h b/block-sha1/sha1.h
> > index 6ff59b2..b864df6 100644
> > --- a/block-sha1/sha1.h
> > +++ b/block-sha1/sha1.h
> > @@ -7,9 +7,9 @@
> >   */
> >  
> >  typedef struct {
> > +	unsigned long long size;
> >  	unsigned int H[5];
> >  	unsigned int W[16];
> > -	unsigned long long size;
> >  } blk_SHA_CTX;
> 
> By the reasoning suggested in the commit message, should H[5] not go to 
> the end?

Both arrays are based of unsigned ints which have the same alignment rules. Furthermore the size and H members are much more used than the W member, and keeping them close should help with CPU cache locality.

Nicolas