Reoriented Normal Mapping (http://blog.selfshadow.com/publications/blending-in-detail/) for unpacked, normalised vectors

gistfile1.txt

// Blending when n1 and n2 are already 'unpacked' and normalised
float3 blend_rnm_unpacked(float3 n1, float3 n2)
{
    float3 t = n1.xyz + float3( 0,  0, 1);
    float3 u = n2.xyz * float3(-1, -1, 1);
    float3 r = (t/t.z)*dot(t, u) - u;
    return r;
}