Re: symbols.c: scm_strhash question

[Jim Blandy <jimb@red-bean.com>]

>  What is the magic constant 264 in `scm_strhash()'?

It's a magic constant!

To be honest, that is Aubrey's code, and I don't entirely understand
its design.  It looks as if, if the string being hashed is longer than
five characters, the hash function sort of samples five characters at
random from the string, and ignores the rest.  264 is just the seed
value for the hash accumulator.

Hash functions are a weird area, because the requirements on a hash
function are pretty open-ended --- the value doesn't have to mean
anything --- and the quality of a given hash function depends on the
data you apply it to.  So their design seems like somewhat of a black
art: "season with prime numbers to taste."  I can show a graph of how
well a bunch of hash functions perform, but it's difficult to say
*why* a given function is better...