7.15.1 Vector Literals and Concatenation

You can specify the values to use for vector initialization or assignment using literals or scalar variables. When all of the components assigned to a vector are constants, the result is a vector literal. Otherwise, the vector's value is determined at run-time.

For example, the values assigned to vec_a and vec_b in the following declarations are vector literals and are known during compilation:

short4 vec_a = (short4)(1, 2, 3, 4);
float2 vec_b = (float2)(3.2, -2.3);

The following statement initializes all the elements of the vector to the same value, which is 1 in this case:

ushort4 myushort4 = (ushort4)(1);

The value of myvec in the following function is not resolved until run-time:

void foo(int a, int b) 
{ 
    int2 myvec = (int2)(a, b); ...
}

Shorter vectors can be concatenated together to form longer vectors. In the following example, two int variables are concatenated into an int2 variable:

void foo(int a, int b)
{
    int2 myvec = (int2)(a, b); 
    ...
}

The following example concatenates two int2 variables into an int4 variable, which is passed to an external function:

extern void bar(int4 v4);

void foo(int a, int b)
{
   int2 myv2_a = (int2)(a, 1);
   int2 myv2_b = (int2)(b, 2);

   int4 myv4 = (int4)(myv2_a, myv2_b);

   bar(myv4);
}