I need some help on how to use the SSE logical instructions on Visual Studio. Based on the MSDN website ,
__m128 _mm_and_ps(__m128 a , __m128 b );
ANDPS
can be used to perform logical AND on the operands a and b . But I couldn't figure out the exact steps needed to get the results back (memory load and initialization, set, store, etc).
Specifically, I'd like to know how to:
Could someone please show me in an example how this can be done?
Thanks!
Here's an example - inverting the sign of all the elements in a float vector using XOR:
__m128 v1 = _mm_set_ps(0.0f, 1.0f, -1.0f, -2.0f);
// v1 = 0.0f, 1.0f, -1.0f, -2.0f
__m128 sign = _mm_set1_ps(-0.0f); // sign = -0.0f, -0.0f, -0.0f, -0.0f
__m128 v2 = _mm_xor_ps(v1, sign); // v2 = -0.0f, -1.0f, 1.0f, 2.0f
So, supposing you wanted to negate all the values in an array, you could do it 4 elements at a time, like this:
const int N = 1024;
float a[N];
const __m128 sign = _mm_set1_ps(-0.0f);// sign = -0.0f, -0.0f, -0.0f, -0.0f
for (int i = 0; i < N; i += 4)
{
v = _mm_loadu_ps(&a[i]); // load 4 elements (unaligned) from a[]
v = _mm_xor_ps(v1, sign); // invert sign bit (i.e. negate)
_mm_storeu_ps(&a[i], v); // store 4 elements (unaligned) back to a[]
}
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