sp-cid 0.3.0

Cid library for `no_std` use within Substrate
Documentation 
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use core::convert::TryFrom;

use alloc::vec::Vec;

use sp_multihash::{
  Code,
  Multihash,
  MultihashDigest,
};

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

use crate::{
  Cid,
  Version,
};

impl Arbitrary for Version {
  fn arbitrary<G: Gen>(g: &mut G) -> Self {
    let version = if g.gen_bool(0.7) { 1 } else { 0 };
    Version::try_from(version).unwrap()
  }
}

impl Arbitrary for Cid {
  fn arbitrary<G: Gen>(g: &mut G) -> Self {
    let version: Version = Arbitrary::arbitrary(g);
    if version == Version::V0 {
      let data: Vec<u8> = Arbitrary::arbitrary(g);
      let hash = Code::Sha2_256.digest(&data);
      Cid::new_v0(hash).expect("sha2_256 is a valid hash for cid v0")
    }
    else {
      // In real world lower IPLD Codec codes more likely to happen, hence
      // distribute them with bias towards smaller values.
      let weights = [128, 32, 4, 4, 2, 2, 1, 1];
      let dist = WeightedIndex::new(weights.iter()).unwrap();
      let codec = 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!(),
      };

      let hash: Multihash = Arbitrary::arbitrary(g);
      Cid::new_v1(codec, hash)
    }
  }
}