Merge rust-bitcoin/rust-bitcoin#1053: Implement iter::size_hint and ExactSizeIterator for Witness Iter

ec8dadaf86 Implement iter::size_hint and ExactSizeIterator for Witness Iter (Riccardo Casatta)

Pull request description:

  close https://github.com/rust-bitcoin/rust-bitcoin/issues/1050

  I don't think we need to change the `collect` since it use the `size_hint()` lower bound to initially allocate

  // with size_hint
  // test blockdata::witness::benches::bench_big_witness_to_vec              ... bench:         313 ns/iter (+/- 13)
  // test blockdata::witness::benches::bench_witness_to_vec                  ... bench:         204 ns/iter (+/- 11)

  // without
  // test blockdata::witness::benches::bench_big_witness_to_vec              ... bench:         489 ns/iter (+/- 28)
  // test blockdata::witness::benches::bench_witness_to_vec                  ... bench:         221 ns/iter (+/- 102)

  The reason why the small witness doesn't get big perf boost is because by default vec allocates 4 slots

ACKs for top commit:
  Kixunil:
    ACK ec8dadaf86
  apoelstra:
    ACK ec8dadaf86

Tree-SHA512: dbe09ba6ebd4014fe0639412894beedab6cc7e844a5ec1697af8f0694b62ae5d423a801df1b48ac7029444c01877975e2d5168728f038fbd4f5808bda90e0f2f
This commit is contained in:
Andrew Poelstra 2022-06-16 13:33:26 +00:00
commit e7a3bdda66
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GPG Key ID: C588D63CE41B97C1
1 changed files with 59 additions and 6 deletions

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@ -43,7 +43,10 @@ pub struct Witness {
} }
/// Support structure to allow efficient and convenient iteration over the Witness elements /// Support structure to allow efficient and convenient iteration over the Witness elements
pub struct Iter<'a>(::core::slice::Iter<'a, u8>); pub struct Iter<'a> {
inner: core::slice::Iter<'a, u8>,
remaining: usize,
}
impl Decodable for Witness { impl Decodable for Witness {
fn consensus_decode<D: Read>(mut d: D) -> Result<Self, Error> { fn consensus_decode<D: Read>(mut d: D) -> Result<Self, Error> {
@ -172,7 +175,7 @@ impl Witness {
/// Returns a struct implementing [`Iterator`] /// Returns a struct implementing [`Iterator`]
pub fn iter(&self) -> Iter { pub fn iter(&self) -> Iter {
Iter(self.content.iter()) Iter { inner: self.content.iter(), remaining: self.witness_elements }
} }
/// Returns the number of elements this witness holds /// Returns the number of elements this witness holds
@ -253,18 +256,25 @@ impl<'a> Iterator for Iter<'a> {
type Item = &'a [u8]; type Item = &'a [u8];
fn next(&mut self) -> Option<Self::Item> { fn next(&mut self) -> Option<Self::Item> {
let varint = VarInt::consensus_decode(self.0.as_slice()).ok()?; let varint = VarInt::consensus_decode(self.inner.as_slice()).ok()?;
self.0.nth(varint.len() - 1)?; // VarInt::len returns at least 1 self.inner.nth(varint.len() - 1)?; // VarInt::len returns at least 1
let len = varint.0 as usize; let len = varint.0 as usize;
let slice = &self.0.as_slice()[..len]; let slice = &self.inner.as_slice()[..len];
if len > 0 { if len > 0 {
// we don't need to advance if the element is empty // we don't need to advance if the element is empty
self.0.nth(len - 1)?; self.inner.nth(len - 1)?;
} }
self.remaining -= 1;
Some(slice) Some(slice)
} }
fn size_hint(&self) -> (usize, Option<usize>) {
(self.remaining, Some(self.remaining))
}
} }
impl<'a> ExactSizeIterator for Iter<'a> {}
// Serde keep backward compatibility with old Vec<Vec<u8>> format // Serde keep backward compatibility with old Vec<Vec<u8>> format
#[cfg(feature = "serde")] #[cfg(feature = "serde")]
impl serde::Serialize for Witness { impl serde::Serialize for Witness {
@ -323,6 +333,21 @@ mod test {
assert_eq!(witness.second_to_last(), Some(&[0u8][..])); assert_eq!(witness.second_to_last(), Some(&[0u8][..]));
} }
#[test]
fn test_iter_len() {
let mut witness = Witness::default();
for i in 0..5 {
assert_eq!(witness.iter().len(), i);
witness.push(&vec![0u8]);
}
let mut iter = witness.iter();
for i in (0..=5).rev() {
assert_eq!(iter.len(), i);
iter.next();
}
}
#[test] #[test]
fn test_push_ecdsa_sig() { fn test_push_ecdsa_sig() {
// The very first signature in block 734,958 // The very first signature in block 734,958
@ -408,3 +433,31 @@ mod test {
assert_eq!(new_witness_format, back); assert_eq!(new_witness_format, back);
} }
} }
#[cfg(all(test, feature = "unstable"))]
mod benches {
use test::{Bencher, black_box};
use super::Witness;
#[bench]
pub fn bench_big_witness_to_vec(bh: &mut Bencher) {
let raw_witness = vec![vec![1u8]; 5];
let witness = Witness::from_vec(raw_witness);
bh.iter(|| {
black_box(witness.to_vec());
});
}
#[bench]
pub fn bench_witness_to_vec(bh: &mut Bencher) {
let raw_witness = vec![vec![1u8]; 3];
let witness = Witness::from_vec(raw_witness);
bh.iter(|| {
black_box(witness.to_vec());
});
}
}