Hey, I'm a CS student and I spent the last while building TensorLib: an N-dimensional tensor library with a full reverse-mode autograd engine, written entirely in C, with zero external ML dependencies. It's CPU-only, and you can use it to train an actual GPT-style transformer.
This is a companion discussion topic for the original entry at https://www.reddit.com/r/neuralnetworks/comments/1v8ciar/i_built_a_deep_learning_library_from_scratch_in_c/