95 lines
2.6 KiB
Rust
95 lines
2.6 KiB
Rust
use super::utils::types::{ Sha256Digest };
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use super::blake2::{ Blake2s, Digest };
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use super::config::Config;
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// Interprets a 3-byte slice from a [u8] as an integer.
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fn get_shift_from_source(source: &[u8], offset: usize) -> u32 {
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(source[offset + 2] as u32) |
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((source[offset + 1] as u32) << 8) |
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((source[offset ] as u32) << 16)
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}
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// Given entropy in the form of `seed`, return a shuffled list of validators
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// of size `validator_count` or `sample`.
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pub fn get_shuffling(
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seed: Sha256Digest,
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validator_count: u32,
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sample: Option<u32>,
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config: Config)
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-> Vec<u32>
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{
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let max_validators = config.max_validators;
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assert!(validator_count <= max_validators);
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// TODO: figure out why the Python implementation uses
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// this `rand_max` var.
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// let rand_max = max_validators - (max_validators % validator_count);
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let validator_range = match sample {
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Some(x) => x,
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None => validator_count
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};
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let mut output: Vec<u32> = (0..validator_range).collect();
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let mut source = Blake2s::new();
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source.input(&seed);
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let mut v = 0;
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while v < validator_range {
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let current_source = source.result();
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let mut source_offset = 0;
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while source_offset < 30 {
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let m = get_shift_from_source(¤t_source, source_offset);
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let shuffled_position = (m % (validator_count - v)) + v;
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output.swap(v as usize, shuffled_position as usize);
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v += 1;
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if v >= validator_count { break; }
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source_offset += 3;
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}
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// Re-hash the source
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source = Blake2s::new();
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source.input(¤t_source);
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}
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output
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_shuffling_shift_fn() {
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let mut x = get_shift_from_source(
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&vec![0_u8, 0, 1],
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0);
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assert_eq!((x as u32), 1);
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x = get_shift_from_source(
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&vec![0_u8, 1, 1],
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0);
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assert_eq!(x, 257);
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x = get_shift_from_source(
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&vec![1_u8, 1, 1],
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0);
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assert_eq!(x, 65793);
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x = get_shift_from_source(
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&vec![255_u8, 1, 1],
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0);
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assert_eq!(x, 16711937);
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}
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#[test]
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fn test_shuffling() {
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let s = get_shuffling(
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Sha256Digest::zero(),
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10,
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None,
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Config::standard());
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assert_eq!(s,
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vec!(0, 9, 7, 6, 4, 1, 8, 5, 2, 3),
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"10 validator shuffle was not as expected");
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}
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}
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