Make Fq/Fr similar to each other.
This commit is contained in:
Sean Bowe
parent
e3766101f4
commit
b54b846b50
86
src/fr.rs
86
src/fr.rs
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@ -1,3 +1,6 @@
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//! This module provides an implementation of the Jubjub scalar field $\mathbb{F}_r$
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//! where `r = 0x0e7db4ea6533afa906673b0101343b00a6682093ccc81082d0970e5ed6f72cb7`
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use core::convert::TryInto;
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use core::fmt;
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use core::ops::{Add, AddAssign, Mul, MulAssign, Neg, Sub, SubAssign};
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@ -6,7 +9,8 @@ use subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption};
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use crate::util::{adc, mac, sbb};
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/// Represents an element of `GF(r)`.
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/// Represents an element of the scalar field $\mathbb{F}_r$ of the Jubjub elliptic
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/// curve construction.
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// The internal representation of this type is four 64-bit unsigned
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// integers in little-endian order. Elements of Fr are always in
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// Montgomery form; i.e., Fr(a) = aR mod r, with R = 2^256.
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@ -40,6 +44,7 @@ impl ConstantTimeEq for Fr {
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}
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impl PartialEq for Fr {
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#[inline]
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fn eq(&self, other: &Self) -> bool {
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self.ct_eq(other).unwrap_u8() == 1
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}
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@ -70,19 +75,7 @@ impl<'a> Neg for &'a Fr {
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#[inline]
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fn neg(self) -> Fr {
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// Subtract `self` from `MODULUS` to negate. Ignore the final
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// borrow because it cannot underflow; self is guaranteed to
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// be in the field.
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let (d0, borrow) = sbb(MODULUS.0[0], self.0[0], 0);
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let (d1, borrow) = sbb(MODULUS.0[1], self.0[1], borrow);
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let (d2, borrow) = sbb(MODULUS.0[2], self.0[2], borrow);
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let (d3, _) = sbb(MODULUS.0[3], self.0[3], borrow);
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// `tmp` could be `MODULUS` if `self` was zero. Create a mask that is
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// zero if `self` was zero, and `u64::max_value()` if self was nonzero.
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let mask = u64::from((self.0[0] | self.0[1] | self.0[2] | self.0[3]) == 0).wrapping_sub(1);
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Fr([d0 & mask, d1 & mask, d2 & mask, d3 & mask])
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self.neg()
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}
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}
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@ -100,24 +93,16 @@ impl<'a, 'b> Sub<&'b Fr> for &'a Fr {
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#[inline]
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fn sub(self, rhs: &'b Fr) -> Fr {
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self.subtract(rhs)
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self.sub(rhs)
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}
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}
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impl<'a, 'b> Add<&'b Fr> for &'a Fr {
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type Output = Fr;
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#[allow(clippy::suspicious_arithmetic_impl)]
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#[inline]
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fn add(self, rhs: &'b Fr) -> Fr {
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let (d0, carry) = adc(self.0[0], rhs.0[0], 0);
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let (d1, carry) = adc(self.0[1], rhs.0[1], carry);
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let (d2, carry) = adc(self.0[2], rhs.0[2], carry);
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let (d3, _) = adc(self.0[3], rhs.0[3], carry);
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// Attempt to subtract the modulus, to ensure the value
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// is smaller than the modulus.
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Fr([d0, d1, d2, d3]) - &MODULUS
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self.add(rhs)
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}
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}
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@ -128,7 +113,7 @@ impl<'a, 'b> Mul<&'b Fr> for &'a Fr {
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fn mul(self, rhs: &'b Fr) -> Fr {
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// Schoolbook multiplication
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self.multiply(rhs)
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self.mul(rhs)
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}
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}
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@ -171,20 +156,20 @@ impl Default for Fr {
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impl Fr {
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/// Returns zero, the additive identity.
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#[inline]
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pub fn zero() -> Fr {
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pub const fn zero() -> Fr {
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Fr([0, 0, 0, 0])
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}
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/// Returns one, the multiplicative identity.
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#[inline]
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pub fn one() -> Fr {
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pub const fn one() -> Fr {
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R
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}
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/// Doubles this field element.
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#[inline]
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pub fn double(&self) -> Fr {
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self + self
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pub const fn double(&self) -> Fr {
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self.add(self)
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}
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/// Attempts to convert a little-endian byte representation of
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@ -268,9 +253,9 @@ impl Fr {
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}
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/// Converts from an integer represented in little endian
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/// into its (congruent) representation in Fr.
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/// into its (congruent) `Fr` representation.
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pub const fn from_raw(val: [u64; 4]) -> Self {
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Fr(val).multiply(&R2)
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(&Fr(val)).mul(&R2)
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}
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/// Squares this element.
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@ -508,11 +493,12 @@ impl Fr {
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let (r7, _) = adc(r7, carry2, carry);
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// Result may be within MODULUS of the correct value
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Fr([r4, r5, r6, r7]).subtract(&MODULUS)
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(&Fr([r4, r5, r6, r7])).sub(&MODULUS)
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}
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/// Multiplies this element by another element
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#[inline]
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const fn multiply(&self, rhs: &Self) -> Self {
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pub const fn mul(&self, rhs: &Self) -> Self {
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// Schoolbook multiplication
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let (r0, carry) = mac(0, self.0[0], rhs.0[0], 0);
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@ -538,8 +524,9 @@ impl Fr {
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Fr::montgomery_reduce(r0, r1, r2, r3, r4, r5, r6, r7)
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}
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/// Subtracts another element from this element.
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#[inline]
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const fn subtract(&self, rhs: &Self) -> Self {
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pub const fn sub(&self, rhs: &Self) -> Self {
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let (d0, borrow) = sbb(self.0[0], rhs.0[0], 0);
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let (d1, borrow) = sbb(self.0[1], rhs.0[1], borrow);
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let (d2, borrow) = sbb(self.0[2], rhs.0[2], borrow);
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@ -554,6 +541,37 @@ impl Fr {
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Fr([d0, d1, d2, d3])
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}
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/// Adds this element to another element.
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#[inline]
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pub const fn add(&self, rhs: &Self) -> Self {
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let (d0, carry) = adc(self.0[0], rhs.0[0], 0);
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let (d1, carry) = adc(self.0[1], rhs.0[1], carry);
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let (d2, carry) = adc(self.0[2], rhs.0[2], carry);
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let (d3, _) = adc(self.0[3], rhs.0[3], carry);
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// Attempt to subtract the modulus, to ensure the value
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// is smaller than the modulus.
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(&Fr([d0, d1, d2, d3])).sub(&MODULUS)
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}
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/// Negates this element.
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#[inline]
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pub const fn neg(&self) -> Self {
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// Subtract `self` from `MODULUS` to negate. Ignore the final
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// borrow because it cannot underflow; self is guaranteed to
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// be in the field.
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let (d0, borrow) = sbb(MODULUS.0[0], self.0[0], 0);
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let (d1, borrow) = sbb(MODULUS.0[1], self.0[1], borrow);
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let (d2, borrow) = sbb(MODULUS.0[2], self.0[2], borrow);
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let (d3, _) = sbb(MODULUS.0[3], self.0[3], borrow);
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// `tmp` could be `MODULUS` if `self` was zero. Create a mask that is
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// zero if `self` was zero, and `u64::max_value()` if self was nonzero.
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let mask = (((self.0[0] | self.0[1] | self.0[2] | self.0[3]) == 0) as u64).wrapping_sub(1);
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Fr([d0 & mask, d1 & mask, d2 & mask, d3 & mask])
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}
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}
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impl<'a> From<&'a Fr> for [u8; 32] {
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@ -23,6 +23,12 @@
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#![deny(missing_docs)]
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#![deny(unsafe_code)]
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// This lint is described at
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// https://rust-lang.github.io/rust-clippy/master/index.html#suspicious_arithmetic_impl
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// In our library, some of the arithmetic will necessarily involve various binary
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// operators, and so this lint is triggered unnecessarily.
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#![allow(clippy::suspicious_arithmetic_impl)]
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#[cfg(feature = "std")]
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#[macro_use]
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extern crate std;
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