Re: block-sha1: improve code on large-register-set machines

From: Brandon Casey <brandon.casey.ctr@nrlssc.navy.mil>
Date: Aug 11, 2009, 21:20 UTC
Message-ID: <fLYKSyures_wcvAvAV9-MgKQlhk959HJpx-pKz7T1n-Mel7f2RBkMw@cipher.nrlssc.navy.mil>
In-Reply-To: <alpine.LFD.2.00.0908111517390.10633@xanadu.home>

Nicolas Pitre wrote:

Show 28 quoted lines

> On Tue, 11 Aug 2009, Nicolas Pitre wrote:
> 
>> On Tue, 11 Aug 2009, Linus Torvalds wrote:
>>
>>> On Tue, 11 Aug 2009, Nicolas Pitre wrote:
>>>> #define SHA_SRC(t) \
>>>>   ({ unsigned char *__d = (unsigned char *)&data[t]; \
>>>>      (__d[0] << 24) | (__d[1] << 16) | (__d[2] << 8) | (__d[3] << 0); })
>>>>
>>>> And this provides the exact same performance as the ntohl() based 
>>>> version (4.980s) except that this now cope with unaligned buffers too.
>>> The actual object SHA1 calculations are likely not aligned (we do that 
>>> object header thing), and if you can't do the htonl() any better way I 
>>> guess the byte-based thing is the way to go..
> 
> OK, even better: 4.400s.
> 
> This is with this instead of the above:
> 
> #define SHA_SRC(t) \
>    ({   unsigned char *__d = (unsigned char *)data; \
>         (__d[(t)*4 + 0] << 24) | (__d[(t)*4 + 1] << 16) | \
>         (__d[(t)*4 + 2] <<  8) | (__d[(t)*4 + 3] <<  0); })
> 
> The previous version would allocate a new register for __d and then 
> index it with an offset of 0, 1, 2 or 3.  This version always uses the 
> register containing the data pointer with absolute offsets.  The binary 
> is a bit smaller too.

In that case, why not change the interface of blk_SHA1Block() so that its second argument is const unsigned char* and get rid of __d and the { } ?

Then it will look like this:

   static void blk_SHA1Block(blk_SHA_CTX *ctx, const unsigned char *data);

...

   #define SHA_SRC(t) \
       ( (data[(t)*4 + 0] << 24) | (data[(t)*4 + 1] << 16) | \
         (data[(t)*4 + 2] <<  8) | (data[(t)*4 + 3] <<  0) )

Plus, we need something like the following to handle storing the hash to an unaligned buffer (warning copy/pasted):

@@ -73,8 +74,12 @@ void blk_SHA1_Final(unsigned char hashout[20], blk_SHA_CTX *c
 
        /* Output hash
         */
-       for (i = 0; i < 5; i++)
-               ((unsigned int *)hashout)[i] = htonl(ctx->H[i]);
+       for (i = 0; i < 5; i++) {
+               *hashout++ = (unsigned char) (ctx->H[i] >> 24);
+               *hashout++ = (unsigned char) (ctx->H[i] >> 16);
+               *hashout++ = (unsigned char) (ctx->H[i] >> 8);
+               *hashout++ = (unsigned char) (ctx->H[i] >> 0);
+       }
 }
 
 #if defined(__i386__) || defined(__x86_64__)


With these two changes plus a few other minor tweaks, the block-sha1 code compiles
and passes the test suite on sparc (solaris 7) and mips (irix 6.5).

-brandon