memxor

[Nikos Mavrogiannopoulos]

Hello,
 I've run some tests with memxor on a x86-64 machine. My results are:
* C implementation (compiled with gcc 4.4):
        Xoring in chunks of 32768 bytes: done. 50.09 Gb in 5.00 secs:
10.02 Gb/sec
        Xoring (unaligned) in chunks of 32768 bytes: done. 39.90 Gb in
5.00 secs: 7.98 Gb/sec

* ASM implementation:
        Xoring in chunks of 32768 bytes: done. 38.32 Gb in 5.00 secs:
7.66 Gb/sec
        Xoring (unaligned) in chunks of 32768 bytes: done. 30.16 Gb in
5.00 secs: 6.03 Gb/sec

It seems that in x86-64 the ASM version is slower than the C one.
Moreover I noticed that the loop unrolling techniques used in the C
code have no visible performance benefit.

However, an SSE2 version of memxor (attached) increases performance by
30% or more in the same CPU.

* SSE2:
        Xoring in chunks of 32768 bytes: done. 69.94 Gb in 5.00 secs:
13.98 Gb/sec
        Xoring (unaligned) in chunks of 32768 bytes: done. 65.96 Gb in
5.00 secs: 13.19 Gb/sec

regards,
Nikos
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