SSE code to set float variable to 0.0f or 1.0f based on comparison

Question

I have two arrays: char* c and float* f and I need to do this operation:

// Compute float mask
float* f;
char* c;
char c_thresh;
int n;

for ( int i = 0; i < n; ++i )
{
    if ( c[i] < c_thresh ) f[i] = 0.0f;
    else                   f[i] = 1.0f;
}

I am looking for a fast way to do it: without conditionals and using SSE (4.2 or AVX) if possible.

If using float instead of char can result in faster code, I can change my code to use floats only:

// Compute float mask
float* f;
float* c;
float c_thresh;
int n;

for ( int i = 0; i < n; ++i )
{
    if ( c[i] < c_thresh ) f[i] = 0.0f;
    else                   f[i] = 1.0f;
}

Thanks

Answer 1

Pretty easy, just do the comparison, convert bytes to dword, AND with 1.0f: (not tested, and this isn't meant to be copy&paste code anyway, it's meant to show how you do it)

movd xmm0, [c]          ; read 4 bytes from c
pcmpgtb xmm0, threshold ; compare (note: comparison is >, not >=, so adjust threshold)
pmovzxbd xmm0, xmm0     ; convert bytes to dwords
pand xmm0, one          ; AND all four elements with 1.0f
movdqa [f], xmm0        ; save result

Should be pretty easy to convert to intrinsics.