__m128i变量是零吗？

Question

如何测试__m128i变量在SSE-2及更早版本的处理器上是否具有任何非零值？

Answer 1

In SSE2 you can do:

__m128i zero = _mm_setzero_si128();
if(_mm_movemask_epi8(_mm_cmpeq_epi32(x,zero)) == 0xFFFF)
{
    //the code...
}

this will test four int's vs zero then return a mask for each byte, so your bit-offsets of each corresponding int would be at 0, 4, 8 & 12, but the above test will catch if any bit is set, then if you preserve the mask you can work with the finer grained parts directly if need be.

Answer 2

For the sake of completeness, with SSE4 one can use _mm_testz_si128 .

const bool isAllZero = _mm_testz_si128(a,a);

Note that this is true when all bits are zero .