Ternary operation for vector (select)

I want to know how to use the ternary operator for vector in openCL. I think it should be ‘select’, in the specification:


page 219

say, I have a float4 for each work-item(thread)

float4 a,b,c;
// I want to do this for every component, i.e. y, z, w
if (a.xb.x>0)

I think writing it like this will slow down the program. I tried to use ‘select’, to just use one line, but don’t know how… Could anyone give me an example?

Thank you very much.

// 4-tuple integer
int4 myResult;

// Variable to hold boolean condition
int4 c;

// Component wise compare -- 
//   According to the spec:
//   These functions shall return a 0 if the specified relation 
//   is false and a –1 (i.e. all bits set) if the specified relation 
//   is true for vector argument types.
//   Most Significant Bit (MSB)
//   Translation: If true, MSB is set. 
//                       If false, it is not set.

c = isgreater( a * b, 0)

// c should now have each entry with MSB set or unset

// Can do the ternary comparison now
// If true then (parameter 1): 2 * a * b
// If false then (parameter 0): 0
myResult = select(0, a*b*2, c);

I didn’t check if this would compile. I constructed this from pp 218-219.