"Data from input reused three times (immediately reused in next two i-loop...)" -- can think from an array element's perspective. If you are sitting at input[i], you will have 3 encounters with the 3x1 kernel as it moves from left to right; first time you are at position 2, second time 1 and last time 0. After that, you are useless and can be discarded.
"Data from input reused three times (immediately reused in next two i-loop...)" -- can think from an array element's perspective. If you are sitting at input[i], you will have 3 encounters with the 3x1 kernel as it moves from left to right; first time you are at position 2, second time 1 and last time 0. After that, you are useless and can be discarded.