Dear Ger Hobbelt and Dave Thompson, Thanks for the wealth of information and free lecture. Now, I have followed the simple memcpy function you gave earlier, and I have a simple question, which is faster ? 1. Memcpy 2. (data[n] & 0xFF) | (data[n+1]<<8 & 0xFF00) | (data[n+2]<<16 & 0xFF0000) | (data[n+3]<<24 & 0xFF000000);
I measured the clock cycles my system takes, and it seems memcpy is slower than a simple byte alignment function. > #2 (and this is what the crypto hardware needs!) not only must the > input be word-aligned, its *length* > must also be word-aligned. (That's where 'padding' comes in) > > wordsize=8, input length = 21, then the solution is QUITE different: > > 1 2 3 | 4 5 6 7 8 9 0 1 | 2 3 4 5 6 7 8 9 | 0 1 > > must be *moved* (copy is fine too ;-) ) to an _aligned_ buffer, i.e. > > -> 1 2 3 4 5 6 7 8 | 9 0 1 2 3 4 5 6 | 7 8 9 0 1 > > and padded: > > -> 1 2 3 4 5 6 7 8 | 9 0 1 2 3 4 5 6 | 7 8 9 0 1 p p p | Yes, this is my scenario (case 2). > Sigh. Too bad you're not on M68K hardware or other machinery which > simply (and quite fatally) bombs out on you at a hardware level when > addressing words at UNaligned boundaries. Ah, those were the days... > Java doesn't care any more. (Oops, sorry. let's stop this rant in its > tracks!) > > > If you run on Intel (and you very probably are), you don't get that > penalty, so (performance degrading!) unaligned word accesses will > 'work'. Combine this with your given fault description, then consider > that 'aligning the data' /may/ not be the answer you seek -- mark the > mention of the padding in passing. Consider it a hint that other > things may be wrong with your code. (hint != answer) I am using a soft CPU called Nios II (Verilog based CPU from Altera). I am running uClinux. Unaligned access does not work for me. I now am able to get my system working. And I fixed the 'free bugs' in you code based on Dave's suggestion. Regards, Vishnu. _________________________________________________________________ Easily publish your photos to your Spaces with Photo Gallery. http://get.live.com/photogallery/overview
