* 0b011 to indicate "constant 1" (or 1.0)
* 0b1NN index 0 thru 3 to copy from subelement in pos XYZW
-Evaluating efforts to encode 12 bit swizzle into less proved unsuccessful: 7^4 comes out to 2,400 which is larger than 11 bits.
-
Note that 7 options are needed (not 6) because the 7th option allows static
predicate masking to be encoded within the swizzle immediate.
For example this allows "W.Y." to specify: "copy W to position X,