I am trying to understand some shader code written in ARB. I am mostly using this to understand it. However the doc doesn't explain (or I missed it) how vector operands are transformed into scalars, for example in this expression
MAD.F32 R1.y, R2, R1, R1.w;
R2 and R1 are both 4 components vectors, but the swizzle is unspectified for R2 and the second R1. What is this instruction really doing? My hypothesis was that unspecified components were deduced using the result's component, thus the instruction would by equal to
MAD.F32 R1.y, R2.y, R1.y, R1.w;
but it doesn't seems to be correct.