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Make FieldElement's conditional_assign a trait impl

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Henry de Valence 2017-01-06 12:34:57 -05:00
parent c92ebdd0ac
commit 74049e039e
1 changed files with 39 additions and 34 deletions
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73
src/field.rs
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@ -25,6 +25,7 @@ use std::cmp::{Eq, PartialEq};
use std::ops::Neg;
use util::byte_is_nonzero;
use util::CTAssignable;
/// FieldElements are represented as an array of ten "Limbs", which are radix
/// 25.5, that is, each Limb of a FieldElement alternates between being
@ -142,6 +143,44 @@ impl<'a> Neg for &'a FieldElement {
}
}
impl CTAssignable for FieldElement {
/// Conditionally assign another FieldElement to this one.
///
/// If `choice == 0`, replace `self` with `self`:
///
/// ```
/// # use curve25519_dalek::field::FieldElement;
/// # use curve25519_dalek::util::CTAssignable;
/// let f = FieldElement([1,1,1,1,1,1,1,1,1,1]);
/// let g = FieldElement([2,2,2,2,2,2,2,2,2,2]);
/// let mut h = FieldElement([1,1,1,1,1,1,1,1,1,1]);
/// h.conditional_assign(&g, 0);
/// assert!(h == f);
/// ```
///
/// If `choice == 1`, replace `self` with `f`:
///
/// ```
/// # use curve25519_dalek::field::FieldElement;
/// # use curve25519_dalek::util::CTAssignable;
/// # let f = FieldElement([1,1,1,1,1,1,1,1,1,1]);
/// # let g = FieldElement([2,2,2,2,2,2,2,2,2,2]);
/// # let mut h = FieldElement([1,1,1,1,1,1,1,1,1,1]);
/// h.conditional_assign(&g, 1);
/// assert!(h == g);
/// ```
///
/// # Preconditions
///
/// * `choice` in {0,1}
fn conditional_assign(&mut self, f: &FieldElement, choice: u8) {
let mask = -(choice as Limb);
for i in 0..10 {
self[i] ^= mask & (self[i] ^ f[i]);
}
}
}
/// Convert an array of (at least) three bytes into an i64.
#[inline]
#[allow(dead_code)]
@ -179,40 +218,6 @@ impl FieldElement {
FieldElement([ 1, 0, 0, 0, 0, 0, 0, 0, 0, 0 ])
}
/// Conditionally assign another FieldElement to this one.
///
/// If `choice == 0`, replace `self` with `self`:
///
/// ```
/// # use curve25519_dalek::field::FieldElement;
/// let f = FieldElement([1,1,1,1,1,1,1,1,1,1]);
/// let g = FieldElement([2,2,2,2,2,2,2,2,2,2]);
/// let mut h = FieldElement([1,1,1,1,1,1,1,1,1,1]);
/// h.conditional_assign(&g, 0);
/// assert!(h == f);
/// ```
///
/// If `choice == 1`, replace `self` with `f`:
///
/// ```
/// # use curve25519_dalek::field::FieldElement;
/// # let f = FieldElement([1,1,1,1,1,1,1,1,1,1]);
/// # let g = FieldElement([2,2,2,2,2,2,2,2,2,2]);
/// # let mut h = FieldElement([1,1,1,1,1,1,1,1,1,1]);
/// h.conditional_assign(&g, 1);
/// assert!(h == g);
/// ```
///
/// # Preconditions
///
/// * `choice` in {0,1}
pub fn conditional_assign(&mut self, f: &FieldElement, choice: u8) {
let mask = -(choice as Limb);
for i in 0..10 {
self[i] ^= mask & (self[i] ^ f[i]);
}
}
fn combine_coeffs(input: &[i64;10]) -> FieldElement { //FeCombine
let mut c = [0i64;10];
let mut h = input.clone();