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Add tree shrink fn

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This commit is contained in:
Paul Hauner 2019-04-14 16:31:47 +10:00
parent 582f465ffd
commit 9bc0519092
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GPG Key ID: 303E4494BB28068C
1 changed files with 94 additions and 24 deletions
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118
eth2/utils/ssz/src/cached_tree_hash/resize.rs
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@ -62,6 +62,52 @@ pub fn grow_merkle_cache(
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];
let leaf_level = to_height;
for i in 0..=leaf_level as usize {
let from_i = i + from_height - to_height;
let (from_byte_slice, from_flag_slice) = if from_i == leaf_level {
(
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 == leaf_level {
(
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))?,
)
};
to_byte_slice.copy_from_slice(from_byte_slice.get(0..to_byte_slice.len())?);
to_flag_slice.copy_from_slice(from_flag_slice.get(0..to_flag_slice.len())?);
}
Some((bytes, flags))
}
fn nodes_in_tree_of_height(h: usize) -> usize {
2 * (1 << h) - 1
}
@ -92,18 +138,18 @@ mod test {
use super::*;
#[test]
fn can_grow_three_levels() {
let from: usize = 1;
let to: usize = 15;
fn can_grow_and_shrink_three_levels() {
let small: usize = 1;
let big: usize = 15;
let old_bytes = vec![42; from * HASHSIZE];
let old_flags = vec![false; from];
let original_bytes = vec![42; small * HASHSIZE];
let original_flags = vec![false; small];
let (new_bytes, new_flags) = grow_merkle_cache(
&old_bytes,
&old_flags,
(from + 1).trailing_zeros() as usize - 1,
(to + 1).trailing_zeros() as usize - 1,
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();
@ -144,23 +190,35 @@ mod test {
expected_flags.push(true);
expected_flags.push(true);
assert_eq!(expected_bytes, new_bytes);
assert_eq!(expected_flags, new_flags);
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_one_level() {
let from: usize = 7;
let to: usize = 15;
fn can_grow_and_shrink_one_level() {
let small: usize = 7;
let big: usize = 15;
let old_bytes = vec![42; from * HASHSIZE];
let old_flags = vec![false; from];
let original_bytes = vec![42; small * HASHSIZE];
let original_flags = vec![false; small];
let (new_bytes, new_flags) = grow_merkle_cache(
&old_bytes,
&old_flags,
(from + 1).trailing_zeros() as usize - 1,
(to + 1).trailing_zeros() as usize - 1,
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();
@ -201,7 +259,19 @@ mod test {
expected_flags.push(true);
expected_flags.push(true);
assert_eq!(expected_bytes, new_bytes);
assert_eq!(expected_flags, new_flags);
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);
}
}