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Implement variable-sized windows into multiexp

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Closes https://github.com/serai-dex/serai/issues/17 by using the 
PrimeFieldBits API to do so.

Should greatly speed up small batches, along with batches in the 
hundreds. Saves almost a full second on the cross-group DLEq proof.
This commit is contained in:
Luke Parker
2022-06-30 09:30:24 -04:00
parent 5d115f1e1c
commit 7890827a48
15 changed files with 342 additions and 148 deletions
Download Patch File Download Diff File Expand all files Collapse all files

66
crypto/multiexp/src/straus.rs
View File

@@ -1,66 +1,46 @@
use group::{ff::PrimeField, Group};
use ff::PrimeFieldBits;
use group::Group;
fn prep<G: Group>(pairs: &[(G::Scalar, G)], little: bool) -> (Vec<Vec<u8>>, Vec<[G; 16]>) {
let mut nibbles = vec![];
let mut tables = vec![];
for pair in pairs {
let p = nibbles.len();
nibbles.push(vec![]);
{
let mut repr = pair.0.to_repr();
let bytes = repr.as_mut();
if !little {
bytes.reverse();
}
use crate::{prep_bits, prep_tables};
nibbles[p].resize(bytes.len() * 2, 0);
for i in 0 .. bytes.len() {
nibbles[p][i * 2] = bytes[i] & 0b1111;
nibbles[p][(i * 2) + 1] = (bytes[i] >> 4) & 0b1111;
}
}
tables.push([G::identity(); 16]);
let mut accum = G::identity();
for i in 1 .. 16 {
accum += pair.1;
tables[p][i] = accum;
}
}
(nibbles, tables)
}
pub(crate) fn straus<G: Group>(pairs: &[(G::Scalar, G)], little: bool) -> G {
let (nibbles, tables) = prep(pairs, little);
pub(crate) fn straus<G: Group>(
pairs: &[(G::Scalar, G)],
window: u8
) -> G where G::Scalar: PrimeFieldBits {
let groupings = prep_bits(pairs, window);
let tables = prep_tables(pairs, window);
let mut res = G::identity();
for b in (0 .. nibbles[0].len()).rev() {
for _ in 0 .. 4 {
for b in (0 .. groupings[0].len()).rev() {
for _ in 0 .. window {
res = res.double();
}
for s in 0 .. tables.len() {
res += tables[s][usize::from(nibbles[s][b])];
res += tables[s][usize::from(groupings[s][b])];
}
}
res
}
pub(crate) fn straus_vartime<G: Group>(pairs: &[(G::Scalar, G)], little: bool) -> G {
let (nibbles, tables) = prep(pairs, little);
pub(crate) fn straus_vartime<G: Group>(
pairs: &[(G::Scalar, G)],
window: u8
) -> G where G::Scalar: PrimeFieldBits {
let groupings = prep_bits(pairs, window);
let tables = prep_tables(pairs, window);
let mut res = G::identity();
for b in (0 .. nibbles[0].len()).rev() {
if b != (nibbles[0].len() - 1) {
for _ in 0 .. 4 {
for b in (0 .. groupings[0].len()).rev() {
if b != (groupings[0].len() - 1) {
for _ in 0 .. window {
res = res.double();
}
}
for s in 0 .. tables.len() {
if nibbles[s][b] != 0 {
res += tables[s][usize::from(nibbles[s][b])];
if groupings[s][b] != 0 {
res += tables[s][usize::from(groupings[s][b])];
}
}
}