* Eric Biggers <ebiggers3@xxxxxxxxx> wrote: > There may be a small overhead caused by replacing 'xchg REG, REG' with > the needed sequence 'mov MEM, REG; mov REG, MEM; mov REG, REG' once per > round. But, counterintuitively, when I tested "ctr-twofish-3way" on a > Haswell processor, the new version was actually about 2% faster. > (Perhaps 'xchg' is not as well optimized as plain moves.) XCHG has implicit LOCK semantics on all x86 CPUs, so that's not a surprising result I think. Thanks, Ingo
