where is the zero-padding in input matrix?

[YeeHoming1024]

In the "Convolutional Component" part of the paper, author proposes that since the convolution operation makes the length of the output vector hk less than T, it is necessary to zero-padding on the left of the input matrix X to make the length of the output vector equal to T. However, I don't see any implementation of this in the code. I hope to get a reasonable explanation, thanks!