Vectorize short to float conversion?

Question

I am trying to understand why Visual Studio 2012 (x64) doesn't want to vectorized a conversion from a short to a float . Does anybody have a reason or a way around?

//unsigned short* __restrict A,B,C,D    
for (int j = 0; j < H*W;j++) 
{
    float Gs = D[j]-B[j];
    float Gc = A[j]-C[j];
    in[j]=atan2f(Gs,Gc);
}

info C5002: loop not vectorized due to reason '1101'

RESOLUTION

Runtime using shorts and not vectorizing is about 800ms

Runtime converting to all ints and auto vectorizing is about 140ms (!!!)

Answer 1

From this page , it appears that your "Loop contains a non-vectorizable conversion operation (may be implicit)". Have you tried first converting to a type which is the same width as a float (such as int )?

For a more concrete reason, see here . Apparently, there is no direct way in SSE to convert an SSE register consisting of a vector of shorts to a vector of floats, however there is an instruction that converts 32-bit integers to floats.