beacon 0.2.0

Minimal Serenity beacon chain implementation
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145

#[cfg(feature = "serde")]
mod serde;

#[cfg(feature = "serde")]
pub use self::serde::*;

use crate::{Config, Error};
use crate::primitives::*;
use core::cmp::max;
use primitive_types::H256;

/// Convert integer to bytes.
pub fn to_bytes(v: Uint) -> H256 {
	let bytes = v.to_le_bytes();
	let mut ret = H256::default();
	(&mut ret[0..bytes.len()]).copy_from_slice(&bytes);
	ret
}

/// Convert byte to integer.
pub fn to_uint(v: &[u8]) -> Uint {
	let mut ret = 0u64.to_le_bytes();
	(&mut ret[..]).copy_from_slice(&v[..v.len()]);
	u64::from_le_bytes(ret)
}

/// Get integer squareroot.
pub fn integer_squareroot(n: Uint) -> Uint {
	let mut x = n;
	let mut y = (x + 1) / 2;
	while y < x {
		x = y;
		y = (x + n / x) / 2
	}
	x
}

/// Compare hash.
pub fn compare_hash(a: &H256, b: &H256) -> core::cmp::Ordering {
	for i in 0..32 {
		if a[i] > b[i] {
			return core::cmp::Ordering::Greater
		} else if a[i] < b[i] {
			return core::cmp::Ordering::Less
		}
	}
	core::cmp::Ordering::Equal
}

/// Compute shuffled index.
pub fn shuffled_index<C: Config>(
	mut index: Uint,
	index_count: Uint,
	seed: H256
) -> Result<ValidatorIndex, Error> {
	if !(index < index_count && index_count <= 2u64.pow(40)) {
		return Err(Error::IndexOutOfRange)
	}

	// Swap or not
	// (https://link.springer.com/content/pdf/10.1007%2F978-3-642-32009-5_1.pdf)
	// See the 'generalized domain' algorithm on page 3

	for round in 0..C::shuffle_round_count() {
		let pivot = to_uint(
			&C::hash(&[
				&seed[..],
				&round.to_le_bytes()[..1]
			])[..8]
		) % index_count;
		let flip = (pivot + index_count - index) % index_count;
		let position = max(index, flip);
		let source = C::hash(&[
			&seed[..],
			&round.to_le_bytes()[..1],
			&(position / 256).to_le_bytes()[..4]
		]);
		let byte = source[((position % 256) / 8) as usize];
		let bit = (byte >> (position % 8)) % 2;
		index = if bit != 0 { flip } else { index };
	}

	Ok(index)
}

/// Compute committee indices.
pub fn compute_committee<C: Config>(
	indices: &[ValidatorIndex],
	seed: H256,
	index: Uint,
	count: Uint,
) -> Result<Vec<ValidatorIndex>, Error> {
	let start = (indices.len() as u64 * index) / count;
	let end = (indices.len() as u64 * (index + 1)) / count;

	(start..end).into_iter().map(move |i| {
		Ok(indices[
			shuffled_index::<C>(i, indices.len() as u64, seed)? as usize
		])
	}).collect::<Result<Vec<_>, Error>>()
}

/// Get epoch of slot.
pub fn epoch_of_slot<C: Config>(slot: Uint) -> Uint {
	slot / C::slots_per_epoch()
}

/// Get start slot of epoch.
pub fn start_slot_of_epoch<C: Config>(epoch: Uint) -> Uint {
	epoch * C::slots_per_epoch()
}

/// Get activation exit epoch.
pub fn activation_exit_epoch<C: Config>(epoch: Uint) -> Uint {
	epoch + 1 + C::activation_exit_delay()
}

/// Check whether given proof is valid merkle branch.
pub fn is_valid_merkle_branch<C: Config>(
	leaf: H256, proof: &[H256], depth: u64, index: u64, root: H256
) -> bool {
	if proof.len() as u64 != depth {
		return false
	}

	let mut value = leaf;
	for i in 0..depth {
		if index / 2u64.pow(i as u32) % 2 != 0 {
			value = C::hash(&[&proof[i as usize][..], &value[..]]);
		} else {
			value = C::hash(&[&value[..], &proof[i as usize][..]]);
		}
	}

	value == root
}

/// BLS signing domain given a domain type and fork version.
pub fn bls_domain(domain_type: u64, fork_version: Version) -> u64 {
	let mut bytes = [0u8; 8];
	(&mut bytes[0..4]).copy_from_slice(&domain_type.to_le_bytes()[0..4]);
	(&mut bytes[4..8]).copy_from_slice(fork_version.as_ref());

	u64::from_le_bytes(bytes)
}