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Auto merge of #61 - ebfull:minor-changes, r=ebfull

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Minor changes
This commit is contained in:
bmerge 2017-10-05 18:36:27 +00:00
commit dfb836170b
2 changed files with 32 additions and 56 deletions
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82
src/bls12_381/ec.rs
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@ -85,6 +85,34 @@ macro_rules! curve_impl {
} }
impl $affine { impl $affine {
/// Attempts to construct an affine point given an x-coordinate. The
/// point is not guaranteed to be in the prime order subgroup.
///
/// If and only if `greatest` is set will the lexicographically
/// largest y-coordinate be selected.
fn get_point_from_x(x: $basefield, greatest: bool) -> Option<$affine> {
// Compute x^3 + b
let mut x3b = x;
x3b.square();
x3b.mul_assign(&x);
x3b.add_assign(&$affine::get_coeff_b());
x3b.sqrt().map(|y| {
let mut negy = y;
negy.negate();
$affine {
x: x,
y: if (y < negy) ^ greatest {
y
} else {
negy
},
infinity: false
}
})
}
fn is_on_curve(&self) -> bool { fn is_on_curve(&self) -> bool {
if self.is_zero() { if self.is_zero() {
true true
@ -781,32 +809,7 @@ pub mod g1 {
// Interpret as Fq element. // Interpret as Fq element.
let x = Fq::from_repr(x).map_err(|e| GroupDecodingError::CoordinateDecodingError("x coordinate", e))?; let x = Fq::from_repr(x).map_err(|e| GroupDecodingError::CoordinateDecodingError("x coordinate", e))?;
// Compute x^3 + b G1Affine::get_point_from_x(x, greatest).ok_or(GroupDecodingError::NotOnCurve)
let mut x3b = x;
x3b.square();
x3b.mul_assign(&x);
x3b.add_assign(&G1Affine::get_coeff_b());
// Attempt to compute y
match x3b.sqrt() {
Some(y) => {
let mut negy = y;
negy.negate();
// Get the parity of the sqrt we found.
let parity = y > negy;
Ok(G1Affine {
x: x,
y: if parity == greatest { y } else { negy },
infinity: false
})
},
None => {
// Point must not be on the curve.
Err(GroupDecodingError::NotOnCurve)
}
}
} }
} }
fn from_affine(affine: G1Affine) -> Self { fn from_affine(affine: G1Affine) -> Self {
@ -1307,32 +1310,7 @@ pub mod g2 {
c1: Fq::from_repr(x_c1).map_err(|e| GroupDecodingError::CoordinateDecodingError("x coordinate (c1)", e))? c1: Fq::from_repr(x_c1).map_err(|e| GroupDecodingError::CoordinateDecodingError("x coordinate (c1)", e))?
}; };
// Compute x^3 + b G2Affine::get_point_from_x(x, greatest).ok_or(GroupDecodingError::NotOnCurve)
let mut x3b = x;
x3b.square();
x3b.mul_assign(&x);
x3b.add_assign(&G2Affine::get_coeff_b());
// Attempt to compute y
match x3b.sqrt() {
Some(y) => {
let mut negy = y;
negy.negate();
// Get the parity of the sqrt we found.
let parity = y > negy;
Ok(G2Affine {
x: x,
y: if parity == greatest { y } else { negy },
infinity: false
})
},
None => {
// Point must not be on the curve.
Err(GroupDecodingError::NotOnCurve)
}
}
} }
} }
fn from_affine(affine: G2Affine) -> Self { fn from_affine(affine: G2Affine) -> Self {

6
src/lib.rs
View File

@ -1,6 +1,5 @@
// This library relies on the Rust nightly compiler's `i128_type` feature. // If the "u128-support" feature is enabled, this library can use
// If that's not okay for you, disable the u128-support feature. (Pass // more efficient arithmetic. Only available in the nightly compiler.
// --no-default-features for example.)
#![cfg_attr(feature = "u128-support", feature(i128_type))] #![cfg_attr(feature = "u128-support", feature(i128_type))]
// `clippy` is a code linting tool for improving code quality by catching // `clippy` is a code linting tool for improving code quality by catching
@ -618,7 +617,6 @@ use self::arith::*;
#[cfg(feature = "u128-support")] #[cfg(feature = "u128-support")]
mod arith { mod arith {
/// Calculate a - b - borrow, returning the result and modifying /// Calculate a - b - borrow, returning the result and modifying
/// the borrow value. /// the borrow value.
#[inline(always)] #[inline(always)]