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Create cached_tree_hash crate.

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This commit is contained in:
Paul Hauner
2019-04-26 09:55:03 +10:00
parent 827e1c62d9
commit b213a5ade4
22 changed files with 800 additions and 1778 deletions
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284
eth2/utils/cached_tree_hash/src/resize.rs Normal file
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use super::*;
use std::cmp::min;
/// New vec is bigger than old vec.
pub fn grow_merkle_cache(
old_bytes: &[u8],
old_flags: &[bool],
from_height: usize,
to_height: usize,
) -> Option<(Vec<u8>, Vec<bool>)> {
// Determine the size of our new tree. It is not just a simple `1 << to_height` as there can be
// an arbitrary number of nodes in `old_bytes` leaves if those leaves are subtrees.
let to_nodes = {
let old_nodes = old_bytes.len() / HASHSIZE;
let additional_nodes = old_nodes - nodes_in_tree_of_height(from_height);
nodes_in_tree_of_height(to_height) + additional_nodes
};
let mut bytes = vec![0; to_nodes * HASHSIZE];
let mut flags = vec![true; to_nodes];
let leaf_level = from_height;
for i in 0..=from_height as usize {
// If we're on the leaf slice, grab the first byte and all the of the bytes after that.
// This is required because we can have an arbitrary number of bytes at the leaf level
// (e.g., the case where there are subtrees as leaves).
//
// If we're not on a leaf level, the number of nodes is fixed and known.
let (old_byte_slice, old_flag_slice) = if i == leaf_level {
(
old_bytes.get(first_byte_at_height(i)..)?,
old_flags.get(first_node_at_height(i)..)?,
)
} else {
(
old_bytes.get(byte_range_at_height(i))?,
old_flags.get(node_range_at_height(i))?,
)
};
let new_i = i + to_height - from_height;
let (new_byte_slice, new_flag_slice) = if i == leaf_level {
(
bytes.get_mut(first_byte_at_height(new_i)..)?,
flags.get_mut(first_node_at_height(new_i)..)?,
)
} else {
(
bytes.get_mut(byte_range_at_height(new_i))?,
flags.get_mut(node_range_at_height(new_i))?,
)
};
new_byte_slice
.get_mut(0..old_byte_slice.len())?
.copy_from_slice(old_byte_slice);
new_flag_slice
.get_mut(0..old_flag_slice.len())?
.copy_from_slice(old_flag_slice);
}
Some((bytes, flags))
}
/// New vec is smaller than old vec.
pub fn shrink_merkle_cache(
from_bytes: &[u8],
from_flags: &[bool],
from_height: usize,
to_height: usize,
to_nodes: usize,
) -> Option<(Vec<u8>, Vec<bool>)> {
let mut bytes = vec![0; to_nodes * HASHSIZE];
let mut flags = vec![true; to_nodes];
for i in 0..=to_height as usize {
let from_i = i + from_height - to_height;
let (from_byte_slice, from_flag_slice) = if from_i == from_height {
(
from_bytes.get(first_byte_at_height(from_i)..)?,
from_flags.get(first_node_at_height(from_i)..)?,
)
} else {
(
from_bytes.get(byte_range_at_height(from_i))?,
from_flags.get(node_range_at_height(from_i))?,
)
};
let (to_byte_slice, to_flag_slice) = if i == to_height {
(
bytes.get_mut(first_byte_at_height(i)..)?,
flags.get_mut(first_node_at_height(i)..)?,
)
} else {
(
bytes.get_mut(byte_range_at_height(i))?,
flags.get_mut(node_range_at_height(i))?,
)
};
let num_bytes = min(from_byte_slice.len(), to_byte_slice.len());
let num_flags = min(from_flag_slice.len(), to_flag_slice.len());
to_byte_slice
.get_mut(0..num_bytes)?
.copy_from_slice(from_byte_slice.get(0..num_bytes)?);
to_flag_slice
.get_mut(0..num_flags)?
.copy_from_slice(from_flag_slice.get(0..num_flags)?);
}
Some((bytes, flags))
}
fn nodes_in_tree_of_height(h: usize) -> usize {
2 * (1 << h) - 1
}
fn byte_range_at_height(h: usize) -> Range<usize> {
let node_range = node_range_at_height(h);
node_range.start * HASHSIZE..node_range.end * HASHSIZE
}
fn node_range_at_height(h: usize) -> Range<usize> {
first_node_at_height(h)..last_node_at_height(h) + 1
}
fn first_byte_at_height(h: usize) -> usize {
first_node_at_height(h) * HASHSIZE
}
fn first_node_at_height(h: usize) -> usize {
(1 << h) - 1
}
fn last_node_at_height(h: usize) -> usize {
(1 << (h + 1)) - 2
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn can_grow_and_shrink_three_levels() {
let small: usize = 1;
let big: usize = 15;
let original_bytes = vec![42; small * HASHSIZE];
let original_flags = vec![false; small];
let (grown_bytes, grown_flags) = grow_merkle_cache(
&original_bytes,
&original_flags,
(small + 1).trailing_zeros() as usize - 1,
(big + 1).trailing_zeros() as usize - 1,
)
.unwrap();
let mut expected_bytes = vec![];
let mut expected_flags = vec![];
// First level
expected_bytes.append(&mut vec![0; 32]);
expected_flags.push(true);
// Second level
expected_bytes.append(&mut vec![0; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_flags.push(true);
expected_flags.push(true);
// Third level
expected_bytes.append(&mut vec![0; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_flags.push(true);
expected_flags.push(true);
expected_flags.push(true);
expected_flags.push(true);
// Fourth level
expected_bytes.append(&mut vec![42; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_flags.push(false);
expected_flags.push(true);
expected_flags.push(true);
expected_flags.push(true);
expected_flags.push(true);
expected_flags.push(true);
expected_flags.push(true);
expected_flags.push(true);
assert_eq!(expected_bytes, grown_bytes);
assert_eq!(expected_flags, grown_flags);
let (shrunk_bytes, shrunk_flags) = shrink_merkle_cache(
&grown_bytes,
&grown_flags,
(big + 1).trailing_zeros() as usize - 1,
(small + 1).trailing_zeros() as usize - 1,
small,
)
.unwrap();
assert_eq!(original_bytes, shrunk_bytes);
assert_eq!(original_flags, shrunk_flags);
}
#[test]
fn can_grow_and_shrink_one_level() {
let small: usize = 7;
let big: usize = 15;
let original_bytes = vec![42; small * HASHSIZE];
let original_flags = vec![false; small];
let (grown_bytes, grown_flags) = grow_merkle_cache(
&original_bytes,
&original_flags,
(small + 1).trailing_zeros() as usize - 1,
(big + 1).trailing_zeros() as usize - 1,
)
.unwrap();
let mut expected_bytes = vec![];
let mut expected_flags = vec![];
// First level
expected_bytes.append(&mut vec![0; 32]);
expected_flags.push(true);
// Second level
expected_bytes.append(&mut vec![42; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_flags.push(false);
expected_flags.push(true);
// Third level
expected_bytes.append(&mut vec![42; 32]);
expected_bytes.append(&mut vec![42; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_flags.push(false);
expected_flags.push(false);
expected_flags.push(true);
expected_flags.push(true);
// Fourth level
expected_bytes.append(&mut vec![42; 32]);
expected_bytes.append(&mut vec![42; 32]);
expected_bytes.append(&mut vec![42; 32]);
expected_bytes.append(&mut vec![42; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_bytes.append(&mut vec![0; 32]);
expected_flags.push(false);
expected_flags.push(false);
expected_flags.push(false);
expected_flags.push(false);
expected_flags.push(true);
expected_flags.push(true);
expected_flags.push(true);
expected_flags.push(true);
assert_eq!(expected_bytes, grown_bytes);
assert_eq!(expected_flags, grown_flags);
let (shrunk_bytes, shrunk_flags) = shrink_merkle_cache(
&grown_bytes,
&grown_flags,
(big + 1).trailing_zeros() as usize - 1,
(small + 1).trailing_zeros() as usize - 1,
small,
)
.unwrap();
assert_eq!(original_bytes, shrunk_bytes);
assert_eq!(original_flags, shrunk_flags);
}
}