openethereum/util/plain_hasher/src/lib.rs

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#[macro_use]
extern crate crunchy;
extern crate ethereum_types;
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use ethereum_types::H256;
use std::collections::{HashMap, HashSet};
use std::hash;
/// Specialized version of `HashMap` with H256 keys and fast hashing function.
pub type H256FastMap<T> = HashMap<H256, T, hash::BuildHasherDefault<PlainHasher>>;
/// Specialized version of `HashSet` with H256 keys and fast hashing function.
pub type H256FastSet = HashSet<H256, hash::BuildHasherDefault<PlainHasher>>;
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/// Hasher that just takes 8 bytes of the provided value.
/// May only be used for keys which are 32 bytes.
#[derive(Default)]
pub struct PlainHasher {
prefix: u64,
}
impl hash::Hasher for PlainHasher {
#[inline]
fn finish(&self) -> u64 {
self.prefix
}
#[inline]
#[allow(unused_assignments)]
fn write(&mut self, bytes: &[u8]) {
debug_assert!(bytes.len() == 32);
let mut bytes_ptr = bytes.as_ptr();
let mut prefix_ptr = &mut self.prefix as *mut u64 as *mut u8;
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unroll! {
for _i in 0..8 {
unsafe {
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*prefix_ptr ^= (*bytes_ptr ^ *bytes_ptr.offset(8)) ^ (*bytes_ptr.offset(16) ^ *bytes_ptr.offset(24));
bytes_ptr = bytes_ptr.offset(1);
prefix_ptr = prefix_ptr.offset(1);
}
}
}
}
}
#[cfg(test)]
mod tests {
use std::hash::Hasher;
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use super::PlainHasher;
#[test]
fn it_works() {
let mut bytes = [32u8; 32];
bytes[0] = 15;
let mut hasher = PlainHasher::default();
hasher.write(&bytes);
assert_eq!(hasher.prefix, 47);
}
}