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perf/refactor(precompile): simplify bn128 precompile implementations #1074

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Feb 11, 2024
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perf/refactor(precompile): simplify bn128 precompile implementations #1074

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134 changes: 61 additions & 73 deletions crates/precompile/src/bn128.rs
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Original file line number Diff line number Diff line change
@@ -1,10 +1,13 @@
use crate::{
primitives::U256, Address, Error, Precompile, PrecompileResult, PrecompileWithAddress,
utilities::get_right_padded, Address, Error, Precompile, PrecompileResult,
PrecompileWithAddress,
};
use alloc::vec::Vec;
use bn::{AffineG1, AffineG2, Fq, Fq2, Group, Gt, G1, G2};

pub mod add {
use super::*;

const ADDRESS: Address = crate::u64_to_address(6);

pub const ISTANBUL: PrecompileWithAddress = PrecompileWithAddress(
Expand All @@ -30,7 +33,9 @@ pub mod add {

pub mod mul {
use super::*;

const ADDRESS: Address = crate::u64_to_address(7);

pub const ISTANBUL: PrecompileWithAddress = PrecompileWithAddress(
ADDRESS,
Precompile::Standard(|input: &[u8], gas_limit: u64| -> PrecompileResult {
Expand All @@ -54,6 +59,7 @@ pub mod mul {

pub mod pair {
use super::*;

const ADDRESS: Address = crate::u64_to_address(8);

const ISTANBUL_PAIR_PER_POINT: u64 = 34_000;
Expand Down Expand Up @@ -94,19 +100,31 @@ const MUL_INPUT_LEN: usize = 128;
/// Pair element length.
const PAIR_ELEMENT_LEN: usize = 192;

/// Reads the `x` and `y` points from an input at a given position.
fn read_point(input: &[u8], pos: usize) -> Result<bn::G1, Error> {
use bn::{AffineG1, Fq, Group, G1};

let mut px_buf = [0u8; 32];
px_buf.copy_from_slice(&input[pos..(pos + 32)]);
let px = Fq::from_slice(&px_buf).map_err(|_| Error::Bn128FieldPointNotAMember)?;
/// Reads a single `Fq` from the input slice.
///
/// # Panics
///
/// Panics if the input is not at least 32 bytes long.
#[inline]
fn read_fq(input: &[u8]) -> Result<Fq, Error> {
Fq::from_slice(&input[..32]).map_err(|_| Error::Bn128FieldPointNotAMember)
}

let mut py_buf = [0u8; 32];
py_buf.copy_from_slice(&input[(pos + 32)..(pos + 64)]);
let py = Fq::from_slice(&py_buf).map_err(|_| Error::Bn128FieldPointNotAMember)?;
/// Reads the `x` and `y` points from the input slice.
///
/// # Panics
///
/// Panics if the input is not at least 64 bytes long.
#[inline]
fn read_point(input: &[u8]) -> Result<G1, Error> {
let px = read_fq(&input[0..32])?;
let py = read_fq(&input[32..64])?;
new_g1_point(px, py)
}

if px == Fq::zero() && py == bn::Fq::zero() {
/// Creates a new `G1` point from the given `x` and `y` coordinates.
fn new_g1_point(px: Fq, py: Fq) -> Result<G1, Error> {
if px == Fq::zero() && py == Fq::zero() {
Ok(G1::zero())
} else {
AffineG1::new(px, py)
Expand All @@ -116,18 +134,10 @@ fn read_point(input: &[u8], pos: usize) -> Result<bn::G1, Error> {
}

fn run_add(input: &[u8]) -> Result<Vec<u8>, Error> {
use bn::AffineG1;

let input = if input.len() < ADD_INPUT_LEN {
let mut input = input.to_vec();
input.resize(ADD_INPUT_LEN, 0);
input
} else {
input[..ADD_INPUT_LEN].to_vec()
};
let input = get_right_padded::<ADD_INPUT_LEN>(input, 0);

let p1 = read_point(&input, 0)?;
let p2 = read_point(&input, 64)?;
let p1 = read_point(&input[..64])?;
let p2 = read_point(&input[64..])?;

let mut output = [0u8; 64];
if let Some(sum) = AffineG1::from_jacobian(p1 + p2) {
Expand All @@ -145,24 +155,18 @@ fn run_add(input: &[u8]) -> Result<Vec<u8>, Error> {
}

fn run_mul(input: &[u8]) -> Result<Vec<u8>, Error> {
use bn::AffineG1;
let input = get_right_padded::<MUL_INPUT_LEN>(input, 0);

let mut input = input.to_vec();
input.resize(MUL_INPUT_LEN, 0);
let p = read_point(&input[..64])?;

let p = read_point(&input, 0)?;

let mut fr_buf = [0u8; 32];
fr_buf.copy_from_slice(&input[64..96]);
// Fr::from_slice can only fail on incorrect length, and this is not a case.
let fr = bn::Fr::from_slice(&fr_buf[..]).unwrap();
// `Fr::from_slice` can only fail when the length is not 32.
let fr = bn::Fr::from_slice(&input[64..96]).unwrap();

let mut out = [0u8; 64];
if let Some(mul) = AffineG1::from_jacobian(p * fr) {
mul.x().to_big_endian(&mut out[..32]).unwrap();
mul.y().to_big_endian(&mut out[32..]).unwrap();
}

Ok(out.to_vec())
}

Expand All @@ -177,68 +181,52 @@ fn run_pair(
return Err(Error::OutOfGas);
}

use bn::{AffineG1, AffineG2, Fq, Fq2, Group, Gt, G1, G2};

if input.len() % PAIR_ELEMENT_LEN != 0 {
return Err(Error::Bn128PairLength);
}

let output = if input.is_empty() {
U256::from(1)
let success = if input.is_empty() {
true
} else {
let elements = input.len() / PAIR_ELEMENT_LEN;
let mut vals = Vec::with_capacity(elements);

const PEL: usize = PAIR_ELEMENT_LEN;

let mut mul = Gt::one();
for idx in 0..elements {
let mut buf = [0u8; 32];

buf.copy_from_slice(&input[(idx * PEL)..(idx * PEL + 32)]);
let ax = Fq::from_slice(&buf).map_err(|_| Error::Bn128FieldPointNotAMember)?;
buf.copy_from_slice(&input[(idx * PEL + 32)..(idx * PEL + 64)]);
let ay = Fq::from_slice(&buf).map_err(|_| Error::Bn128FieldPointNotAMember)?;
buf.copy_from_slice(&input[(idx * PEL + 64)..(idx * PEL + 96)]);
let bay = Fq::from_slice(&buf).map_err(|_| Error::Bn128FieldPointNotAMember)?;
buf.copy_from_slice(&input[(idx * PEL + 96)..(idx * PEL + 128)]);
let bax = Fq::from_slice(&buf).map_err(|_| Error::Bn128FieldPointNotAMember)?;
buf.copy_from_slice(&input[(idx * PEL + 128)..(idx * PEL + 160)]);
let bby = Fq::from_slice(&buf).map_err(|_| Error::Bn128FieldPointNotAMember)?;
buf.copy_from_slice(&input[(idx * PEL + 160)..(idx * PEL + 192)]);
let bbx = Fq::from_slice(&buf).map_err(|_| Error::Bn128FieldPointNotAMember)?;

let a = {
if ax.is_zero() && ay.is_zero() {
G1::zero()
} else {
G1::from(AffineG1::new(ax, ay).map_err(|_| Error::Bn128AffineGFailedToCreate)?)
}
let read_fq_at = |n: usize| {
debug_assert!(n < PAIR_ELEMENT_LEN / 32);
let start = idx * PAIR_ELEMENT_LEN + n * 32;
// SAFETY: We're reading `6 * 32 == PAIR_ELEMENT_LEN` bytes from `input[idx..]`
// per iteration. This is guaranteed to be in-bounds.
let slice = unsafe { input.get_unchecked(start..start + 32) };
Fq::from_slice(slice).map_err(|_| Error::Bn128FieldPointNotAMember)
};
let ax = read_fq_at(0)?;
let ay = read_fq_at(1)?;
let bay = read_fq_at(2)?;
let bax = read_fq_at(3)?;
let bby = read_fq_at(4)?;
let bbx = read_fq_at(5)?;

let a = new_g1_point(ax, ay)?;
let b = {
let ba = Fq2::new(bax, bay);
let bb = Fq2::new(bbx, bby);

if ba.is_zero() && bb.is_zero() {
G2::zero()
} else {
G2::from(AffineG2::new(ba, bb).map_err(|_| Error::Bn128AffineGFailedToCreate)?)
}
};
vals.push((a, b))
}

let mul = vals
.into_iter()
.fold(Gt::one(), |s, (a, b)| s * bn::pairing(a, b));

if mul == Gt::one() {
U256::from(1)
} else {
U256::ZERO
mul = mul * bn::pairing(a, b);
}

mul == Gt::one()
};

Ok((gas_used, output.to_be_bytes_vec()))
let mut out = [0u8; 32];
out[31] = success as u8;
Ok((gas_used, out.to_vec()))
}

/*
Expand Down
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