Assigning float4 to float array opencl - c++

Question

i am trying to optimize a simple opencl kernel using float4 instead of float.
This is the example code without float4.
example code:
__kernel void Substract (
__global const float* data,
const float val,
__global float* result
){
size_t gi = get_global_id(0);
float input_val = data[gi];
result[gi] = val - input_val;
}
My idea for float4:
__kernel void substract (
__global const float* data,
const float val,
__global float* result
){
size_t gi = get_global_id(0);
float4 val2 = float4 (val,val,val,val);
float4 input_val = data[gi*4];
result[gi] = val2 - input_val;
}
However this does not work, because we can not write back a float4 result into a float array. Is there a performant possibilty to write back float4 to a normal float array in opencl? The simple idea would be a for loop with 4 runs.
I want to optimize the kernel for gpu and cpu.
So if i have a variant with float4 and one without, both should run under the excact same kernel arguments. Is this possible?

Answer 1

You can just declare your arguments as float4 pointers, without changing anything on the host. Also, the compiler should automatically widen scalar values if they are used in expressions containing vectors, so you don't need to manually create a float4 version of val:
__kernel void Substract (
__global const float4* data,
const float val,
__global float4* result
){
size_t gi = get_global_id(0);
float4 input_val = data[gi];
result[gi] = val - input_val;
}