SSE/SIMD shift with one-byte element size / granularity?

Question

As you know we have below Shift instructions in SIMD SSE: PSLL(W-D-Q) and PSRL(W-D-Q)

There\'s no PSLLB instruction, so how ca

Answer 1

Here's another way to emulate "psrab" which works for SSE or AVX with 1 scratch register:

  __ punpckhbw(scratch, src);  // junk in low bytes
  __ punpcklbw(dst, src);      // junk in low bytes
  __ psraw(scratch, 8 + shift);
  __ psraw(dst, 8 + shift);
  __ packsswb(dst, scratch);   // pack words to get result