removes awkward back-and-forth int -> double -> int conversion.
the last step also broke uniformity, though it likely doesn't
matter much in mpv's playlist shuffle context.
mutex itself was probably more costly than the PRNG itself. and
locking PRNGs is almost universally not recommended. simply add
a state parameter that the caller can hold to avoid locks.
When starting multiple processes of `mpv --shuffle` in parallel,
sometimes the random seed happens to be identical, so files are
played in the same random order.
mp_rand_seed(0) now uses a random seed provided by libavutil,
and only falls back to time in case of failure.
Add xoshiro as a PRNG implementation instead of relying
on srand() and rand() from the C standard library. This,
in particular, lets us avoid platform-defined behavior with
respect to threading.
NRK