Nicolas Pitre wrote:
> On Tue, 11 Aug 2009, Brandon Casey wrote:
>
>> Nicolas Pitre wrote:
>>> 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 { } ?
>
> Because not all architectures care to access the data bytewise. Please
> see the original SHA_SRC definition.
You mean this:
#define SHA_SRC(t) htonl(data[t])
? Or was there a definition before this one?
I don't follow what you are saying. Are you saying that the following two
examples are different?
unsigned int *data;
#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); })
and
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) )
-brandon
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