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Tidy up sinsemilla_hash_to_point() with bitvec

This commit is contained in:
Deirdre Connolly 2021-04-29 23:37:46 -04:00
parent 42999b2112
commit d0180423c1
1 changed files with 6 additions and 16 deletions
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22
zebra-chain/src/orchard/sinsemilla.rs
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@ -51,12 +51,12 @@ fn Q(D: &[u8]) -> pallas::Point {
/// ///
/// https://zips.z.cash/protocol/nu5.pdf#concretesinsemillahash /// https://zips.z.cash/protocol/nu5.pdf#concretesinsemillahash
#[allow(non_snake_case)] #[allow(non_snake_case)]
fn S(j: &u16) -> pallas::Point { fn S(j: &BitSlice<Lsb0, u8>) -> pallas::Point {
// The value of j is a 10-bit value, therefore must never exceed 2^10 in // The value of j is a 10-bit value, therefore must never exceed 2^10 in
// value. // value.
assert!(j < &1024u16); assert_eq!(j.len(), 10);
pallas_group_hash(b"z.cash:SinsemillaS", &j.to_le_bytes()) pallas_group_hash(b"z.cash:SinsemillaS", j.as_slice())
} }
/// "...an algebraic hash function with collision resistance (for fixed input /// "...an algebraic hash function with collision resistance (for fixed input
@ -87,21 +87,11 @@ pub fn sinsemilla_hash_to_point(D: &[u8], M: &BitVec<Lsb0, u8>) -> pallas::Point
// https://zips.z.cash/protocol/nu5.pdf#concretesinsemillahash // https://zips.z.cash/protocol/nu5.pdf#concretesinsemillahash
for chunk in M.chunks(k) { for chunk in M.chunks(k) {
// Pad each chunk with zeros. // Pad each chunk with zeros.
let mut store = 0u16; let mut store = [0u8; 2];
let bits = store.bits_mut::<Lsb0>(); let bits = store.bits_mut::<Lsb0>();
chunk bits[..chunk.len()].copy_from_slice(&chunk);
.iter()
.enumerate()
.for_each(|(i, bit)| bits.set(i, *bit));
// An instance of LEBS2IP_k acc = acc + acc + S(&bits[..k]);
// XXX: does Rust or bitvec have a better implementation?
let j = &bits
.iter()
.enumerate()
.fold(0u16, |j, (i, &bit)| j + if bit { 1 << i } else { 0 });
acc = acc + acc + S(j);
} }
acc acc