Best way to zero out all channels except the greatest

Is there a better way to do this. I am just hoping I am not doing something grossly inefficient. Criticism is welcome.

Code (CSharp):

1.             // Return a float4 where each channel is zero except the channel with the greatest value.
2.             float4 SingleOut(float4 col)
3.             {
4.                 float4 colTemp = col;
5.                 colTemp.r = col.r >= col.b? col.r>=col.g ? col.r >= col.a?col.r + col.g+col.b+col.a:0:0:0;
6.                 colTemp.g = col.g >= col.a? col.g>col.r ? col.g >= col.b?col.r + col.g+col.b+col.a:0:0:0;
7.                 colTemp.b = col.b > col.g? col.b>=col.a ? col.b > col.r?col.r + col.g+col.b+col.a:0:0:0;
8.                 colTemp.a = col.a > col.r? col.a>col.b ? col.a > col.g?col.r + col.g+col.b+col.a:0:0:0;
9.                 return colTemp;
10.             }

 

Guess it’s perfect. I am shader god.

 

Code (CSharp):

1. greatest = max(max(col.r, col.g), max(col.b, col.a));
2. col.r = col.r >= greatest ? col.r : 0.0;
3. col.g = col.g >= greatest ? col.g : 0.0;
4. col.b = col.b >= greatest ? col.b : 0.0;
5. col.a = col.a >= greatest ? col.a : 0.0;

or even simpler

Code (CSharp):

1. greatest = max(max(col.r, col.g), max(col.b, col.a));
2. mask = saturate((col - greatest + 0.0001) * 100000.0);
3. col *= mask;

 

I would like to note. The provided solution doesn’t provide 1:1 results where multiple channels have the max value. For example, with the input float4(1,1,0,0) will return float4(1,1,0,0), where as the original provides foat4(1,0,0,0).
I didn’t specify that in the comment so it is understandable.
The solution provided can be reworked to return the same results so it is not a big deal. Thank you!