Just looking at the first lines of the linked code, I see the following:
// Define a custom hash function to use instead of khash's default hash
// function. This custom hash function uses a simpler bit shift and XOR which
// results in several percent faster performance compared to when khash's
// default hash function is used.
That is picking terms. Many languages don't allow to specify custom hash functions, so you can't specify the hash functions until you do write a custom hash table. A fair benchmark would allow for this, if it is allowed in C.
The OP "Performance comparison: counting words in Python, Go, C++, C, Awk, Forth, Rust" does not allow external libraries BUT then makes an exception for C, and then makes a further exception -- In the optimized version we’ll roll our own hash table.
Wikipedia is your friend -- "A hash table uses a hash function to compute an index, also called a hash code …"
I was not talking about the article but the benchmark site linked. Not sure what you want to say with the wikipedia citation.
I have not made a comprehensive list, but the topic has come up when discussing one of the Go benchmarks. The Go language has a build-in hashtable, called a map, and this does not allow to specify custom hash functions. Of course rolling out a hashtable implementation which does allow this is prohibited by the benchmark rules. Probably intentionally, also like your distraction attempts are hinting to.
