No, it doesn't shift across 64-bit boundaries. Take a look at the gcc output in your link ``` movdqa xmm0, XMMWORD PTR [rdi] movdqa xmm1, xmm0 psrlq xmm0, 10 psrldq xmm1, 8 psllq xmm1, 54 por xmm0, xmm1 movdqa xmm1, XMMWORD PTR .LC0[rip] ```

That's a lot of psr and psl instructions for a "single 128-bit wide shift"...