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Extend Field and Checksum for error correction #203

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Merged
apoelstra merged 6 commits into from
Sep 19, 2024
Merged

Extend Field and Checksum for error correction #203

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8eaec9d
field: use UFCS in macro
apoelstra Sep 18, 2024
3c97cd1
field: split trait into "normal" field trait and sealed trait
apoelstra Sep 18, 2024
011674d
field: add format_as_rust_code utility method
apoelstra Mar 30, 2024
14e4f7b
field: add Default bound to Field
apoelstra Sep 14, 2024
c389d72
checksum: add new error-correction fields to the Checksum trait
apoelstra Sep 18, 2024
f47ec0b
field: add Powers iterator
apoelstra Sep 18, 2024
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109 changes: 61 additions & 48 deletions src/primitives/field.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -51,29 +51,6 @@ pub trait Field:
/// prime factors which each appearing once, this array would have size `2^n`.
const MULTIPLICATIVE_ORDER_FACTORS: &'static [usize];

/// Adds a value to `self`. This is a helper function for implementing the
/// [`ops::Add`] and [`ops::AddAssign`] traits, which should probably be called
/// instead of calling this.
fn _add(&self, other: &Self) -> Self;

/// Subtracts a value from `self`. This is a helper function for implementing the
/// [`ops::Sub`] and [`ops::SubAssign`] traits, which should probably be called
/// instead of calling this.
fn _sub(&self, other: &Self) -> Self;

/// Multiplies a value by `self`. This is a helper function for implementing the
/// [`ops::Mul`] and [`ops::MulAssign`] traits, which should probably be called
/// instead of calling this.
fn _mul(&self, other: &Self) -> Self;

/// Divides a value from `self`. This is a helper function for implementing the
/// [`ops::Div`] and [`ops::DivAssign`] traits, which should probably be called
/// instead of calling this.
fn _div(&self, other: &Self) -> Self;

/// Computes the additive inverse of an element.
fn _neg(self) -> Self;

/// Computes the multiplicative inverse of an element.
fn multiplicative_inverse(self) -> Self;

Expand Down Expand Up @@ -141,169 +118,205 @@ pub trait ExtensionField: Field + From<Self::BaseField> {
const EXT_ELEM: Self;
}

mod private {
/// Sealing trait.
pub trait Sealed {}
Comment on lines +138 to +139
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@clarkmoody clarkmoody Sep 19, 2024

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This is clever 👌


impl Sealed for crate::Fe32 {}
impl Sealed for crate::Fe1024 {}
impl Sealed for crate::Fe32768 {}
}

/// Sealed trait which extends [`Field`] with extra functionality
/// needed internally to this library.
///
/// This trait should not be used directly by users of the library.
pub trait Bech32Field: private::Sealed + Sized {
/// Adds a value to `self`. This is a helper function for implementing the
/// [`ops::Add`] and [`ops::AddAssign`] traits.
fn _add(&self, other: &Self) -> Self;

/// Subtracts a value from `self`. This is a helper function for implementing the
/// [`ops::Sub`] and [`ops::SubAssign`] traits.
fn _sub(&self, other: &Self) -> Self {
self._add(other) // all fields in this library are binary fields
}

/// Multiplies a value by `self`. This is a helper function for implementing the
/// [`ops::Mul`] and [`ops::MulAssign`] traits.
fn _mul(&self, other: &Self) -> Self;

/// Divides a value from `self`. This is a helper function for implementing the
/// [`ops::Div`] and [`ops::DivAssign`] traits.
fn _div(&self, other: &Self) -> Self;

/// Computes the additive inverse of an element.
fn _neg(self) -> Self;
}

macro_rules! impl_ops_for_fe {
(impl for $op:ident) => {
// add
impl core::ops::Add<$op> for $op {
type Output = Self;
#[inline]
fn add(self, other: $op) -> $op { $crate::primitives::Field::_add(&self, &other) }
fn add(self, other: $op) -> $op { $crate::primitives::Bech32Field::_add(&self, &other) }
}

impl core::ops::Add<&$op> for $op {
type Output = Self;
#[inline]
fn add(self, other: &$op) -> $op { $crate::primitives::Field::_add(&self, other) }
fn add(self, other: &$op) -> $op { $crate::primitives::Bech32Field::_add(&self, other) }
}

impl core::ops::Add<$op> for &$op {
type Output = $op;
#[inline]
fn add(self, other: $op) -> $op { $crate::primitives::Field::_add(self, &other) }
fn add(self, other: $op) -> $op { $crate::primitives::Bech32Field::_add(self, &other) }
}

impl core::ops::Add<&$op> for &$op {
type Output = $op;
#[inline]
fn add(self, other: &$op) -> $op { $crate::primitives::Field::_add(self, other) }
fn add(self, other: &$op) -> $op { $crate::primitives::Bech32Field::_add(self, other) }
}

impl core::ops::AddAssign for $op {
#[inline]
fn add_assign(&mut self, other: $op) {
*self = $crate::primitives::Field::_add(self, &other)
*self = $crate::primitives::Bech32Field::_add(self, &other)
}
}

impl core::ops::AddAssign<&$op> for $op {
#[inline]
fn add_assign(&mut self, other: &$op) {
*self = $crate::primitives::Field::_add(self, other)
*self = $crate::primitives::Bech32Field::_add(self, other)
}
}

// sub
impl core::ops::Sub<$op> for $op {
type Output = Self;
#[inline]
fn sub(self, other: $op) -> $op { $crate::primitives::Field::_sub(&self, &other) }
fn sub(self, other: $op) -> $op { $crate::primitives::Bech32Field::_sub(&self, &other) }
}

impl core::ops::Sub<&$op> for $op {
type Output = Self;
#[inline]
fn sub(self, other: &$op) -> $op { $crate::primitives::Field::_sub(&self, other) }
fn sub(self, other: &$op) -> $op { $crate::primitives::Bech32Field::_sub(&self, other) }
}

impl core::ops::Sub<$op> for &$op {
type Output = $op;
#[inline]
fn sub(self, other: $op) -> $op { $crate::primitives::Field::_sub(self, &other) }
fn sub(self, other: $op) -> $op { $crate::primitives::Bech32Field::_sub(self, &other) }
}

impl core::ops::Sub<&$op> for &$op {
type Output = $op;
#[inline]
fn sub(self, other: &$op) -> $op { $crate::primitives::Field::_sub(self, other) }
fn sub(self, other: &$op) -> $op { $crate::primitives::Bech32Field::_sub(self, other) }
}

impl core::ops::SubAssign for $op {
#[inline]
fn sub_assign(&mut self, other: $op) {
*self = $crate::primitives::Field::_sub(self, &other)
*self = $crate::primitives::Bech32Field::_sub(self, &other)
}
}

impl core::ops::SubAssign<&$op> for $op {
#[inline]
fn sub_assign(&mut self, other: &$op) {
*self = $crate::primitives::Field::_sub(self, other)
*self = $crate::primitives::Bech32Field::_sub(self, other)
}
}

// mul
impl core::ops::Mul<$op> for $op {
type Output = Self;
#[inline]
fn mul(self, other: $op) -> $op { $crate::primitives::Field::_mul(&self, &other) }
fn mul(self, other: $op) -> $op { $crate::primitives::Bech32Field::_mul(&self, &other) }
}

impl core::ops::Mul<&$op> for $op {
type Output = Self;
#[inline]
fn mul(self, other: &$op) -> $op { $crate::primitives::Field::_mul(&self, other) }
fn mul(self, other: &$op) -> $op { $crate::primitives::Bech32Field::_mul(&self, other) }
}

impl core::ops::Mul<$op> for &$op {
type Output = $op;
#[inline]
fn mul(self, other: $op) -> $op { $crate::primitives::Field::_mul(self, &other) }
fn mul(self, other: $op) -> $op { $crate::primitives::Bech32Field::_mul(self, &other) }
}

impl core::ops::Mul<&$op> for &$op {
type Output = $op;
#[inline]
fn mul(self, other: &$op) -> $op { $crate::primitives::Field::_mul(self, other) }
fn mul(self, other: &$op) -> $op { $crate::primitives::Bech32Field::_mul(self, other) }
}

impl core::ops::MulAssign for $op {
#[inline]
fn mul_assign(&mut self, other: $op) {
*self = $crate::primitives::Field::_mul(self, &other)
*self = $crate::primitives::Bech32Field::_mul(self, &other)
}
}

impl core::ops::MulAssign<&$op> for $op {
#[inline]
fn mul_assign(&mut self, other: &$op) {
*self = $crate::primitives::Field::_mul(self, other)
*self = $crate::primitives::Bech32Field::_mul(self, other)
}
}

// div
impl core::ops::Div<$op> for $op {
type Output = Self;
#[inline]
fn div(self, other: $op) -> $op { $crate::primitives::Field::_div(&self, &other) }
fn div(self, other: $op) -> $op { $crate::primitives::Bech32Field::_div(&self, &other) }
}

impl core::ops::Div<&$op> for $op {
type Output = Self;
#[inline]
fn div(self, other: &$op) -> $op { $crate::primitives::Field::_div(&self, other) }
fn div(self, other: &$op) -> $op { $crate::primitives::Bech32Field::_div(&self, other) }
}

impl core::ops::Div<$op> for &$op {
type Output = $op;
#[inline]
fn div(self, other: $op) -> $op { $crate::primitives::Field::_div(self, &other) }
fn div(self, other: $op) -> $op { $crate::primitives::Bech32Field::_div(self, &other) }
}

impl core::ops::Div<&$op> for &$op {
type Output = $op;
#[inline]
fn div(self, other: &$op) -> $op { $crate::primitives::Field::_div(self, other) }
fn div(self, other: &$op) -> $op { $crate::primitives::Bech32Field::_div(self, other) }
}

impl core::ops::DivAssign for $op {
#[inline]
fn div_assign(&mut self, other: $op) {
*self = $crate::primitives::Field::_div(self, &other)
*self = $crate::primitives::Bech32Field::_div(self, &other)
}
}

impl core::ops::DivAssign<&$op> for $op {
#[inline]
fn div_assign(&mut self, other: &$op) {
*self = $crate::primitives::Field::_div(self, other)
*self = $crate::primitives::Bech32Field::_div(self, other)
}
}

// neg
impl core::ops::Neg for $op {
type Output = Self;
#[inline]
fn neg(self) -> Self { $crate::primitives::Field::_neg(self) }
fn neg(self) -> Self { $crate::primitives::Bech32Field::_neg(self) }
}

// sum
Expand Down
21 changes: 12 additions & 9 deletions src/primitives/gf32.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ use core::{fmt, num};
#[cfg(all(test, mutate))]
use mutagen::mutate;

use super::{Bech32Field, Field};
use crate::error::write_err;

/// Logarithm table of each bech32 element, as a power of alpha = Z.
Expand Down Expand Up @@ -256,16 +257,9 @@ impl AsRef<u8> for Fe32 {
fn as_ref(&self) -> &u8 { &self.0 }
}

impl super::Field for Fe32 {
const ZERO: Self = Fe32::Q;
const ONE: Self = Fe32::P;
const GENERATOR: Self = Fe32::Z;
const MULTIPLICATIVE_ORDER: usize = 31;
const MULTIPLICATIVE_ORDER_FACTORS: &'static [usize] = &[1, 31];

impl Bech32Field for Fe32 {
fn _add(&self, other: &Fe32) -> Fe32 { Fe32(self.0 ^ other.0) }
// Subtraction is the same as addition in a characteristic-2 field
fn _sub(&self, other: &Fe32) -> Fe32 { self._add(other) }

fn _mul(&self, other: &Fe32) -> Fe32 {
if self.0 == 0 || other.0 == 0 {
Fe32(0)
Expand All @@ -276,6 +270,7 @@ impl super::Field for Fe32 {
Fe32(LOG_INV[((log1 + log2) % mult_order) as usize])
}
}

fn _div(&self, other: &Fe32) -> Fe32 {
if self.0 == 0 {
Fe32(0)
Expand All @@ -290,6 +285,14 @@ impl super::Field for Fe32 {
}

fn _neg(self) -> Self { self }
}

impl Field for Fe32 {
const ZERO: Self = Fe32::Q;
const ONE: Self = Fe32::P;
const GENERATOR: Self = Fe32::Z;
const MULTIPLICATIVE_ORDER: usize = 31;
const MULTIPLICATIVE_ORDER_FACTORS: &'static [usize] = &[1, 31];

fn multiplicative_inverse(self) -> Self { Self::ONE._div(&self) }
}
Expand Down
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