[marshray]

> > There are tricks that let them do this 8 bytes at a time (on AMD64, 4 bytes on x86)

> It's actually 16 bytes at a time on any machine that supports SSE (maybe 32 bytes soon with AVX).

Is there a sequence of fewer than 16 instructions to spot a NUL byte inside the 16 byte block?

[haberman]

> Is there a sequence of fewer than 16 instructions to spot a NUL byte inside the 16 byte block?

Yes:

    pxor  %xmm1, %xmm1
    pcmpeqb (mem), %xmm1  // Do 16 byte-wise compares
    pmovmskb %xmm1, %eax  // Move results into the low 16 bits
    test %eax, %eax
    jnz saw_null

[marshray]

Very cool.