Ho,
the implementation is in this 1.3k file. In particular, the forward method (that computed the output) is this 405 one.
Here is a quick description of what the C code is doing:


here 465 check that the input is valid.

here 190 initialize stuff and make the output have the right size.
Then it iterates over the batch 117 then height 43 then width 29.
For each of these, it gets the input coordinated ix and iy here 265.

here 283 it computes the 4 points around it that will be used for the interpolation.

here 106 it computes the weights for each of these 4 points.

here 83 it clips stuff if you asked for it.
Then it iterates over the channels 61.
It get 78 the 4 points values, compute 96 the interpolation value then save 58 it in the output tensor.