[RFC] Bit twiddling API

[Ravenslofty]

(Sorry, I accidentally hit enter)

I'd like to propose some API for things like getting the most/least significant bit index, along with getting the number of set bits in an int.

My main purpose here is to explore how well OCaml works for bitboards, which represent a chessboard as a 64-bit int, with each bit representing the presence/absence of a piece.

This requires a large amount of bit twiddling, for example to serialise given bitboards into moves.

Extracting the MSB/LSB can be done in OCaml purely through your library, but it would benefit heavily from the hardware acceleration of C compiler intrinsics that OCaml doesn't provide.

[mwweissmann]

I would expect using nativeint for this purpose would yield the best results; unfortunately for you, it is only 63 bit wide. Implementing the bit twiddling in C (on an int64) means, that you have to call a C function, which has a little overhead. I suspect that you CPU caches will equalize the difference between a getLSB FFI call and a Int64.(&&) 0x1L (or whatever).