Note that "find ... -exec" is always going to be slow, as it does one process spawn per file. You should process multiple files at once using xargs:

    find . -type f -print0 | xargs -0 xxhsum -r 

As a bonus, you can easily customize it to select only subset of files (find . -type f -name '*.js' -print0) , or to checksum using 16 cores (| xargs -P 16 -0 xxhsum -r)