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use jubjub::*;
use pairing::*;
#[derive(Copy, Clone)]
pub enum Personalization {
NoteCommitment,
MerkleTree(usize)
}
impl Personalization {
pub fn get_bits(&self) -> Vec<bool> {
match *self {
Personalization::NoteCommitment =>
vec![true, true, true, true, true, true],
Personalization::MerkleTree(num) => {
assert!(num < 63);
(0..6).map(|i| (num >> i) & 1 == 1).collect()
}
}
}
}
pub fn pedersen_hash<E, I>(
personalization: Personalization,
bits: I,
params: &E::Params
) -> edwards::Point<E, PrimeOrder>
where I: IntoIterator<Item=bool>,
E: JubjubEngine
{
let mut bits = personalization.get_bits().into_iter().chain(bits.into_iter());
let mut result = edwards::Point::zero();
let mut generators = params.pedersen_hash_exp_table().iter();
loop {
let mut acc = E::Fs::zero();
let mut cur = E::Fs::one();
let mut chunks_remaining = params.pedersen_hash_chunks_per_generator();
let mut encountered_bits = false;
// Grab three bits from the input
while let Some(a) = bits.next() {
encountered_bits = true;
let b = bits.next().unwrap_or(false);
let c = bits.next().unwrap_or(false);
// Start computing this portion of the scalar
let mut tmp = cur;
if a {
tmp.add_assign(&cur);
}
cur.double(); // 2^1 * cur
if b {
tmp.add_assign(&cur);
}
// conditionally negate
if c {
tmp.negate();
}
acc.add_assign(&tmp);
chunks_remaining -= 1;
if chunks_remaining == 0 {
break;
} else {
cur.double(); // 2^2 * cur
cur.double(); // 2^3 * cur
cur.double(); // 2^4 * cur
}
}
if !encountered_bits {
break;
}
let mut table: &[Vec<edwards::Point<E, _>>] = &generators.next().expect("we don't have enough generators");
let window = JubjubBls12::pedersen_hash_exp_window_size();
let window_mask = (1 << window) - 1;
let mut acc = acc.into_repr();
let mut tmp = edwards::Point::zero();
while !acc.is_zero() {
let i = (acc.as_ref()[0] & window_mask) as usize;
tmp = tmp.add(&table[0][i], params);
acc.shr(window);
table = &table[1..];
}
result = result.add(&tmp, params);
}
result
}
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