sp-multihash 0.3.0

use quickcheck::{
  Arbitrary,
  Gen,
};
use rand::{
  distributions::{
    weighted::WeightedIndex,
    Distribution,
  },
  Rng,
};

use crate::MultihashGeneric;

/// Generates a random valid multihash.
impl Arbitrary for MultihashGeneric<64> {
  fn arbitrary<G: Gen>(g: &mut G) -> Self {
    // In real world lower multihash codes are more likely to happen, hence
    // distribute them with bias towards smaller values.
    let weights = [128, 64, 32, 16, 8, 4, 2, 1];
    let dist = WeightedIndex::new(weights.iter()).unwrap();
    let code = match dist.sample(g) {
      0 => g.gen_range(0, u64::pow(2, 7)),
      1 => g.gen_range(u64::pow(2, 7), u64::pow(2, 14)),
      2 => g.gen_range(u64::pow(2, 14), u64::pow(2, 21)),
      3 => g.gen_range(u64::pow(2, 21), u64::pow(2, 28)),
      4 => g.gen_range(u64::pow(2, 28), u64::pow(2, 35)),
      5 => g.gen_range(u64::pow(2, 35), u64::pow(2, 42)),
      6 => g.gen_range(u64::pow(2, 42), u64::pow(2, 49)),
      7 => g.gen_range(u64::pow(2, 56), u64::pow(2, 63)),
      _ => unreachable!(),
    };

    // Maximum size is 64 byte due to the `U64` generic
    let size = g.gen_range(0, 64);
    let mut data = [0; 64];
    g.fill_bytes(&mut data);
    MultihashGeneric::wrap(code, &data[..size]).unwrap()
  }
}