Common API for hashing functions

[edawson]

Writing this down here so I can remember it one day, when I've submitted my thesis...

Right now we have an API for hashing kmers (calc_hash(**)) and reads (calc_hashes(**)). However, these have fixed hash functions (currently MurmerHash64). Ideally, it would be easier if we could drop in new hash functions using a common API rather than the spaghetti code / infinite-if-elif-elses the design currently uses.

I'm imagining a function that takes a string, a start position, an end position, and a std::function that wraps a given hash function with the necessary parameters. The signature might look something like:

mkmh::hash_t calc_hash(char* seq, const size_t& start, const size_t& end, std::function<mkmh::hash_t(char*, int, int, int)>& hashfunc)

where hashfunc is a wrapper around a hash function that might look like:

mkmh::hash_t murmurhash64(const char* seq, int offset, int end, int seed);

It's a little strange passing a nearly identical function to another one, but it means we could use multiple hash functions within mkmh without modifying the API (or even adding to the source code).