Improvement suggestion.
In the following paragraph:
The procedures encode_i_format and decode_i_format in the source code of selfie encode and decode instructions in I-Format, respectively. There are similar procedures for other formats introduced below as well. Note that the source code of selfie mostly uses the keyword uint64_t instead of the keyword int. In C* both keywords mean the same thing: unsigned integer 64-bit type! However, the keyword int actually means something different in standard C which may be confusing to readers who know C. So, here int is just like uint64_t.
The part about usage of uint64_t instead of int seems out of place - it seems weird that this is mentioned in the section on RISC-U. A better place to mention this might be the section on C* that already mentions uint64_t and bootstrapping int to uint64_t.